CLASS 330, AMPLIFIERS SECTION I - CLASS DEFINITION … · April 2009 CLASSIFICATION DEFINITIONS 330 - 1 April 2009 CLASS 330, AMPLIFIERS SECTION I - CLASS DEFINITION (A) This is the

April 2009 CLASSIFICATION DEFINITIONS 330 - 1

April 2009

CLASS 330, AMPLIFIERS

SECTION I - CLASS DEFINITION

(A) This is the generic class for amplifiers as limited bythe definition of amplifiers as it appears in the Glossarybelow.

(B) Included are amplifiers having all types of activeelements (or amplifying devices, the term used in thisclass) as for example vacuum tubes, gas tubes, semicon-ductors, magnetic type saturable reactors, masers, etc..,as set forth in the specific subclasses in the schedule forthe class. Specific types of vacuum tube amplifierdevices included are, traveling wave type tubes, second-ary emission type tubes, electron beam tubes, magne-trons, etc.

(C) Included are amplifier systems having plural ampli-fier channels, cascade amplifiers, push-pull amplifiersand other amplifiers having plural amplifier devices.Also included are amplifiers with plural signal sourcesor plural loads, as for example sum or difference ampli-fiers which have plural sources.

(D) Amplifiers including the means coupling the signalsource to the amplifier or coupling the amplifier to theload or between cascaded stages are also includedherein. Such coupling means include those of the dis-tributed parameter type, resonant tuned circuits, filters,coupling designed to pass a broad band, D.C. coupledcircuits, potentiometer means for volume control, equal-izers, circuits for volume control, etc.

(E) Amplifiers combined with tone control means arealso included herein as indicated in D above for the typeincluded in the amplifier coupling means, also includedherein are those tone control amplifiers relying on signalfeedback means to effect the tone control.

(F) Amplifiers combined with amplitude (volume) con-trol means whether by manual control, by control of anelectrode D.C. bias, as in gain control, or by controllinga variable impedance means for the signal transmissionpath of the amplifier are also included herein.

(G) Amplifiers combined with power supply means forsuch amplifier are also included herein, as well as meansto control the voltage or current of such means.

(H) Amplifiers combined with structural features of theamplifier or the amplifier circuit elements includingstructure of the amplifier device, capacitors, transform-ers, etc.

(I) Amplifiers having signal feedback means.

SECTION II - LINES WITH OTHER CLASSESAND WITHIN THIS CLASS

A. TWO-TERMINAL NEGATIVE RESISTANCENETWORKS

Such networks containing an active element (amplifyingdevice) are not classified in this class, but classifiedelsewhere. (See References to Other Classes, below.)

B. LIMITERS

Passive networks which limit the signal amplitude volt-age or current are classified elsewhere. Miscellaneouslimiting circuits with active device elements are classi-fied elsewhere. (See References to Other Classes,below.)

C. MISCELLANEOUS ELECTRONIC TUBE CIR-CUITS

Circuits including electron tubes (other than the limitersdiscussed above) in which the signal output is not a sub-stantial replica of the input signal, are classified residu-ally elsewhere. Examples of such tube circuits are waveconversion circuits, miscellaneous pulse generating sys-tems, and electronic tube gating circuits. (See Refer-ences to Other Classes, below.)

D. SATURABLE REACTOR CIRCUITS (MAG-NETIC AMPLIFIERS)

Such circuits which control voltage or current and arenot classifiable herein (as for example, where the A.C.power supply current is not removed from the signaloutput by filtering or other means) are classified else-where. Saturable reactor circuits for wave shaping,switching, pulse production, etc., analogous to similarelectronic tube circuits are classified elsewhere withnonlinear reactor systems, and computers using mag-netic amplifiers are also classified elsewhere. (See Ref-erences to Other Classes, below.)

E. NONLINEAR REACTOR CIRCUITS:

Where a nonlinear capacitor serves as the active elementor amplifying device in a circuit which switches, shapesa wave, or produces pulses and is not provided for else-where classification is in Class 307. So called amplifiercircuits including a nonlinear capacitor as the amplify-

330 - 2 CLASSIFICATION DEFINITIONS April 2009

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ing device, which have an A.C. source where the claimsdo not provide a filter to remove the A.C. source fromthe output or where a demodulator is claimed and no fil-ter or other means to remove the A.C. power supplyfrom the signal output circuit is disclosed, are excludedfrom this class. (See References to Other Classes,below.)

F. MISCELLANEOUS TRANSISTOR CIRCUITS:

Transistor circuits which are not amplifiers or not com-bined with an art device or in a system specifically pro-vided for in some class, are classified elsewhere. Suchart as miscellaneous transistor wave shapers, gating cir-cuits, limiters, and pulse producers are classifiedtherein. (See References to Other Classes, below.)

G. AMPLIFIER COMBINED WITH SPECIFICSOURCE OF SIGNAL ENERGY:

This class does not provide for combinations of amplifi-ers with a specific source of electric signal, such as amicrophone which limits the system to use with a partic-ular art even though the source is claimed by name only.Similarly, where the source is claimed by characteristicsspecific to the art device as for example, “a source ofspeech signals” classification is not in this class. How-ever, classification is in this class where the source isclaimed by its electrical characteristics not specific tothe source device, as for example, “a high impedancesource of electrical signal”. Where the specific source,or details thereof are claimed, classification is with theart device so identified. (See References to OtherClasses, below.)

Generator or Oscillator Claimed By Name Only

The terms generator or oscillator in claims, where theyappear as sources of signal energy without further quali-fication except by their electrical characteristics such asimpedance, reactance, etc., are treated as generalizedsources of signal energy, and classification is withamplifiers except where specific details of the generatoror oscillator are claimed; in such cases classification iswith the type of generator claimed or with oscillators.(See References to Other Classes, below.)

H. AMPLIFIERS COMBINED WITH SPECIFICLOAD:

Where the load is claimed, broadly, or by name only as aspecific electrical art device, as for example, as a loud-speaker, classification is not in this class but with theload art device claimed. Where characteristics of the

load device are claimed, which are peculiar to the dis-closed electrical art device or to a specific type of elec-trical art device, classification is with the load art deviceestablished in the claim. Subject matter wherein generalelectrical characteristics of the load are claimed, as forexample, “a load having a variable impedance,” is clas-sified in this or indented subclasses. (See References toOther Classes, below)

I. OSCILLATOR AS A LOAD FOR AN AMPLIFIER

Subject matter wherein an amplifier is combined withan oscillator as load for the amplifier is classified withamplifiers when the oscillator is claimed by name only;where specific details of the oscillator are claimed, clas-sification is elsewhere. (See References to OtherClasses, below.)

J. REPEATERS:

Devices known in the art as repeaters which are in effecttwo-way amplifiers are not classified in this class butare classified elsewhere. (See References to OtherClasses, below.)

K. AMPLIFIERS COMBINED WITH LONG LINETRANSMISSION MEANS OR DISTRIBUTEDPARAMETER ELEMENTS, AND AMPLIFIERSCOMBINED WITH WAVE FILTERS, EQUALIZERSOR ATTENUATORS:

Such subject matter is classified herein even though theamplifier is claimed by name only, if some detail of theco-operation of the amplifier with the passive network(coupling) is claimed. (See References to OtherClasses, below.)

L. COMPANDERS INCLUDING AMPLIFIERS:

Systems including means to compress a signal wave, anelectrically long transmission line and means to expandthe signal wave are not classified herein even when theyinclude details of an amplifier. Companders are classi-fied elsewhere. Amplifiers with compressor orexpander means alone not involving a complete com-pander system are classified herein. Such subcombina-tions involving connection or maintenance of apredetermined condition of the transmission line areclassified elsewhere. Where such connection is of anamplifier condition classification is herein. (See Refer-ences to Other Classes, below.)

M. SYSTEMS INCLUDING PILOT CONTROLMEANS:


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Amplifiers including a pilot control frequency compo-nent in the signal source which is used to control theamplifier are classified herein.

Transmission Lines Combined With Pilot Control -Such subject matter is classified elsewhere when pro-vided with an auxiliary line for the pilot control signal;for those systems in which the pilot control signal iscombined with the signal to be transmitted; with anamplifier which is controlled must correct or maintain apredetermined condition of the transmission line forclassification elsewhere. Otherwise classification isherein.

Pilot Frequency Controlled Repeaters - Such subjectmatter is classified elsewhere.

N. GAS OR VAPOR TUBE CIRCUITS IN OTHERCLASSES:

Gas or vapor tube circuits are classified elsewhere. (SeeReferences to Other Classes and Within This Class.)

O. TRAVELING WAVE TUBES AND CIRCUITS:

Classification of traveling wave tube amplifiers is in thisclass when it includes the output or load circuit. Classi-fication is otherwise where no load or output circuit isclaimed and the circuit means which may be involvedare an integral part of the tube. Oscillators including atraveling wave tube are classified elsewhere. (See Ref-erences to Other Classes, below.)

P. AMPLIFIER AND A DETECTOR OR SUPERHET-ERODYNE CONVERTER AND AN AMPLIFIER:

Such subject matter involves a subcombination peculiarto radio receivers and is classified elsewhere with radioreceivers or in appropriate subclasses for a demodulatorwith amplifier. When an amplifier and a detector areclaimed and the detector is claimed merely as a meansto develop a control signal and not for the purpose ofdetecting the intelligence signal as a function of areceiver, classification is herein and not in receivers.Where the same tube serves both as a detector and anamplifier classification is not in this class but elsewhere.Demodulators, depending again upon the type ofdemodulator involved, are classified elsewhere. Combi-nations which comprise a reflex amplifier or a superre-generative detector are classified elsewhere. (SeeReferences to Other Classes, below.)

Q. VOLTAGE MAGNITUDE CONTROL SYSTEMS:

Voltage magnitude control (for single source energy sys-tems) such as line voltage control, etc., in general, isclassified elsewhere and includes current or load regula-tion, current and voltage limiting systems, transformerand impedance systems for the purpose. See LIMIT-ERS, above. (See References to Other Classes, below.)

R. SYSTEM OR DEVICES CLOSELY RELATED TOOR ANALOGOUS TO AMPLIFIERS:

See References to Other Classes, below.

S. SYSTEMS UTILIZING AMPLIFIERS:

The great majority of electrical control or signaling sys-tems utilize amplifiers such as are classified herein orclosely related devices (as where the waveform of theinput is not retained in the output). Such systemsinclude, also, mechanical systems with electrical controlmeans. In view of such widespread use no attempt ismade to list the classes of all or a large number of sys-tems utilizing amplifiers. Systems involving amplifiersin combinations where the amplifier is invariablypresent, involve few additional elements, or wherein theamplifier is usually an important component of the com-bination are classified elsewhere.

Also see References to Other Classes, below.

T. ELEMENTS OR CIRCUIT NETWORKS COM-MONLY USED IN AMPLIFIERS OR AMPLIFIERSYSTEMS:

See References to Other Classes, below.

SECTION III - REFERENCES TO OTHERCLASSES

SEE OR SEARCH CLASS:174, Electricity: Conductors and Insulators, sub-

classes 32+ for shielding means. (See LinesWith Other Classes, T, “Elements or CircuitNetworks Commonly Used in Amplifiers,”above.)

250, Radiant Energy, appropriate subclasses, for thedetection of invisible radiant energy or the test-ing of materials by invisible radiant energy,subclasses 200+ for photocell circuits andapparatus, particularly subclass 214 for photo-cell controlled circuits including electron tubecircuits. (See Lines With Other Classes, S,“Systems Utilizing Amplifiers,” above.)


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257, Active Solid-State Devices (e.g., Transistors,Solid-State Diodes), for active solid statedevices, per se. (See Lines With Other Classes,T, “Elements or Circuit Networks CommonlyUsed in Amplifiers or Amplifier Systems,”above.)

307, Electrical Transmission or InterconnectionSystems, for saturable reactor circuits for waveshaping, switching, pulse production, etc.,analogous to similar electronic tube circuits;subclasses 401+ for nonlinear reactor sys-tems. So called amplifier circuits including anonlinear capacitor as the amplifying device,which have an A.C. source where the claims donot provide a filter to remove the A.C. sourcefrom the output or where a demodulator isclaimed and no filter or other means to removethe A.C. power supply from the signal outputcircuit is disclosed is classified in subclasses401+. (See Lines With Other Classes, D, “Sat-urable Reactor Circuits (Magnetic Amplifi-ers).” E, “Nonlinear Reactor Circuits.” and R,“System or Devices Closely Related to orAnalogous to Amplifiers,” above.)

313, Electric Lamp and Discharge Devices, appro-priate subclasses for the structure of vacuumtubes and gas and vapor tubes. See the classdefinition of Class 313. (See Lines With OtherClasses, T, “Elements or Circuit NetworksCommonly Used in Amplifiers,” above.)

315, Electric Lamp and Discharge Devices: Sys-tems, for gas or vapor tube circuits in otherclasses; see the classes specified in the Notesthereto for gas or vapor tube circuits. (SeeLines With Other Classes, N, “Gas or VaporTube Circuits in Other Classes.”)

315, Electric Lamp and Discharge Devices: Sys-tems, subclasses 3.5, 3.6 or 39.3 for classifica-tion otherwise where no load or output circuitis claimed and the circuit means which may beinvolved are an integral part of the tube. (LinesWith Other Classes, O, “Traveling WaveTubes and Circuits”).

323, Electricity: Power Supply or Regulation Sys-tems, for passive networks which limit the sig-nal amplitude voltage or current. (Lines WithOther Classes, B, “Limiters.”)

323, Electricity: Power Supply or Regulation Sys-tems, for circuits which control voltage or cur-rent. (See Lines With Other Classes, D, “Satu-rable Reactor Circuits (Magnetic Amplifiers.”)

323, Electricity: Power Supply or Regulation Sys-tems, for voltage magnitude control (for singlesource energy systems) such as line voltage

control, etc., in general (see the class defini-tion). (Lines With Other Classes, “VoltageMagnitude Control Systems”).

324, Electricity: Measuring and Testing, sub-classes 123+ for amplifiers with meters.

327, Miscellaneous Active Electrical NonlinearDevices, Circuits, and Systems, subclasses309+ for miscellaneous limiting circuits withactive device elements.

327, Miscellaneous Active Electrical NonlinearDevices, Circuits, and Systems, subclasses100+ for wave conversion circuits, subclasses291+ for miscellaneous pulse generating sys-tems, and subclasses 365+ for electronic tubegating circuits. (Lines With Other Classes, C,“Miscellaneous Electronic Tube Circuits.”)

327, Miscellaneous Active Electrical NonlinearDevices, Circuits, and Systems, appropriatesubclasses for transistor circuits which are notamplifiers or not combined with an art deviceor in a system specifically provided for in someclass. (See Lines With Other Classes, F, “Mis-cellaneous Transistor Circuits.”)

329, Demodulators, appropriate subclasses for ademodulator with amplifier. (See Lines WithOther Classes, P, “Amplifier and a Detector orSuperheterodyne Converter and an Amplifier”and S, “Systems Utilizing Amplifiers,” above.)

329, Demodulators, where the same tube servesboth as a detector and an amplifier, dependingupon the type of demodulator involved. (LinesWith Other Classes, P, “Amplifier and a Detec-tor or Superheterodyne Converter and anAmplifier”).

331, Oscillators, are in the most common types, in asense, merely positive feedback amplifierswithout an input, and therefore the circuits,structures, and problems are often closelyrelated to those of amplifiers. (See Lines WithOther Classes, R, “System or Devices CloselyRelated to or Analogous to Amplifiers,”above.)

331, Oscillators, where specific details of the gen-erator or oscillator are claimed; in such casesclassification is with the type of generatorclaimed or with oscillators. (See Lines WithOther Classes, G, under “Generator or Oscilla-tor Claimed by Name Only,” and I, “Oscilla-tor as a Load for an Amplifier,” above.)

331, Oscillators, for oscillators including a travelingwave tube; subclass 82 for traveling wave type.(Lines With Other Classes, O, “TravelingWave Tubes and Circuits”).


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332, Modulators, appear, usually as no more thanamplifiers which have an input source in addi-tion to the signal (i.e., the carrier). (See LinesWith Other Classes, R, “System or DevicesClosely Related to or Analogous to Amplifi-ers,” above.)

333, Wave Transmission Lines and Networks,appropriate subclasses, particularly subclasses24+, for passive wave filters and coupling net-works. (See Lines With Other Classes, T, “Ele-ments or Circuit Networks Commonly Used inAmplifiers or Amplifier Systems,” above.)

333, Wave Transmission Lines and Networks, sub-classes 213+for networks containing an activeelement (amplifying device). (See Lines WithOther Classes, A, “Two-Terminal NegativeResistance Networks,” above.)

333, Wave Transmission Lines and Networks, sub-class 14 for companders. Subcombinationsinvolving connection or maintenance of a pre-determined condition of the transmission lineare classified in Class 333. (See Lines WithOther Classes, L, “Companders IncludingAmplifiers.”)

333, Wave Transmission Lines and Networks, sub-class 15, when provided with an auxiliary linefor the pilot control signal, subclass 16 forthose systems in which the pilot control signalis combined with the signal to be transmittedand also subclass 16 with an amplifier which iscontrolled must correct or maintain a predeter-mined condition of the transmission line.(Lines With Other Classes, M, under “Trans-mission Lines Combined With Pilot Control,”above.)

333, Wave Transmission Lines and Networks, forelectric wave transmission systems, passivewave transmission networks, passive couplingnetworks and terminating networks, smoothingtype wave filters, networks including a wavetransmission device, passive networks for pro-ducing an output wave, systems includingactive elements, and wave traps using long lineelements. (Lines With Other Classes, K,“Amplifiers Combined With Long Line Trans-mission Means or Distributed Parameter Ele-ments, and Amplifiers Combined With WaveFilters, Equalizers or Attenuators”).

334, Tuners, appropriate subclasses for tuners, perse. (See Lines With Other Classes, T, “Ele-ments or Circuit Networks Commonly Used inAmplifiers,” above.)

336, Inductor Devices, appropriate subclasses forthe structure of transformers and inductor

devices, generally. (See Lines With OtherClasses, T, “Elements or Circuit NetworksCommonly Used in Amplifiers or AmplifierSystems,” above.)

361, Electricity: Electrical Systems and Devices, subclasses 196+ for electric circuits includingtransistors, subclasses 199+ and 205 for elec-tric circuits including space discharge devicescombined with relays as the load therefor, andsubclass 204 for electric circuits including sat-urable reactors, wherein the transistor, spacedischarge, or saturable reactor circuit may bean amplifier. (See Lines With Other Classes, S,“Systems Utilizing Amplifiers”, above.)

361, Electricity: Electrical Systems and Devices, subclasses 271+ and 500+ for capacitor struc-ture, per se. (See Lines With Other Classes, T,“Elements or Circuit Networks CommonlyUsed in Amplifiers or Amplifier Systems,”above.)

379, Telephonic Communications, subclasses 338+for devices known in the art as repeaters whichare in effect two-way amplifiers. (See LinesWith Other Classes, J, “Repeaters,” above.)

381, Electrical Audio Signal Processing Systemsand Devices, subclasses 111+ for miscella-neous systems which include combinations ofamplifier and loud speaker or microphone andamplifier which limits the system to use with aparticular art even though the source is claimedby name only; for distribution systems, involv-ing a central broadcasting system from whichprograms are distributed to local stations wherethe programs are amplified and reproduced;also for where the load is claimed, broadly, orby name only as a specific electrical art device,as for example, as a loudspeaker. (See LinesWith Other Classes, G, “Amplifier CombinedWith Specific Source of Signal Energy,” H,“Amplifiers Combined With Specific Load,”and S, “Systems Utilizing Amplifiers,”above.)

398, Optical Communication, subclasses 1 through8 for light wave communications. (See LinesWith Other Classes, S, Systems UtilizingAmplifiers, above.)

455, Telecommunications, subclasses 130+ forradio receivers which may be limited to anamplifier and a detector; subclass 351 for por-table radio receivers. (See Lines With OtherClasses, S, “Systems Utilizing Amplifiers,”above.)


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455, Telecommunications, appropriate subclass,particularly subclass 335, where the same tubeserves both as a detector and an amplifier.Class 455, subclass 342, includes combinationswhich comprise a reflex amplifier or sub-classes 336+ for combinations which comprisea superregenerative detector. (Lines WithOther Classes, P, “Amplifier and a Detector orSuperheterodyne Converter and an Amplifier”)

455, Telecommunications, subclasses 130+ for asubcombination peculiar to radio receiversclassified with radio receivers. (See LinesWith Other Classes, P, “Amplifier And aDetector or Superheterodyne Converter AndAn Amplifier.”)

505, Superconductor Technology: Apparatus,Material, Process, subclasses 150+ for hightemperature (Tc 30 K) superconductingdevice; and particularly subclass 180 formaser-type amplifying device, or subclasses191+ for semiconductor device. (See LinesWith Other Classes, R, “System or Devices”Closely Related to or Analogous to Amplifiers,S, “Systems Utilizing Amplifiers”, and T, “Ele-ments or Circuit Networks Commonly Used inAmplifiers,”above.)

SECTION IV - GLOSSARY

ACCEPTOR IMPURITY OR ACCEPTOR

A material which when added to a semiconductor mate-rial in minute quantities, as an impurity, induces holeconduction, generally causing the semiconductor to beone of “P-type conductivity”.

ACTIVE NETWORK

A network containing a source of energy, or a sink ofenergy (i.e., a device for absorbing or dissipating energyother than that accounted for by the resistance of thecomponents of the networks). Merely dissipating theheat generated by a resistance will not cause the resis-tance to be an active element. See Amplifying Device.

AMPLIFIER

Electric circuit means wherein a variable electrical cur-rent or voltage input signal is applied to an electricalamplifying device to control a source of electricalenergy applied to the same device and from which isderived an output signal of substantially the same wave

form as the input signal and substantially linearlyrelated thereto.

AMPLIFIER CHANNEL OR CHANNEL

A part of an amplifier system in which a single signalpath may be traced from a source to a load, and whichpath includes an amplifier as defined above. Such chan-nel may be a cascade amplifier.

AMPLIFYING DEVICE

An electrical transducer of the active type wherein theelectrical energy supplied by one system (power supply)is controlled by the electrical energy supplied by anothersystem (signal source) limited to the active transducerdevice element itself such as a vacuum tube, transistor,controllable gas tube, saturable reactor, variable resis-tive element, etc.. See Active Elements.

AMPLITUDE LIMITER

A means in a circuit to limit the amplitude of the electri-cal voltage across it or the current in it to a value belowor above a fixed predetermined value, particularly theformer.

ANODE

An electrode which acts as the positive terminal of anelectric discharge or which acts as the positive terminalof an electric field to cause a discharge or accelerate theelectrons in an electric discharge.

ATTENUATOR

Devices and networks consisting of one or more ele-ments which exhibit only a positive resistance effect andwhich reduce the intensity of the energy passing throughthe device by dissipation, (1) the elements being propor-tioned to permit a change in their value to control theenergy loss while maintaining substantially constantinput and/or output impedance of the device, and/or (2)the elements being proportioned to permit the device tobe inserted in the circuit to provide an energy loss with-out introducing any reflections in the circuit, and/or (3)the elements being combined with a long line or longline element, and/or (4) the device or network having animpedance equal to the impedance of a specified longline, and/or (5) the device or network is claimed asbeing particularly modified for use over a frequencyband so that its characteristics are particularly related tofrequency.


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AUXILIARY GRID

Any grid, of an electronic tube other than the signalinput grid.

BALANCED CIRCUIT

A circuit having its conductors electrically symmetricalwith respect to a reference potential plane (e.g., ground).The potential between the two sides and ground areequal and of opposite sign. For example, a horizontaltwo-wire line may be a balanced line. See Push-PullStage.

BASE ELECTRODE

See the definition of point contact or junction transistorabove.

BIAS, BIAS VOLTAGE, BIAS CURRENT

In an amplifying device, usually, a steady D.C.. voltageor current applied between two electrodes usuallyreferred to the input electrodes to form an electric refer-ence means for the control means, which influences thecurrent flow of an electronic tube or semiconductordevice or the flux relationships of a magnetic saturablereactor. See also Bias Control and Power Supply.

BIAS CONTROL

Control, as defined above applied to control of bias volt-age or current of an amplifying device. This is distin-guished from signal feedback in that the bias controlvoltage or current has a smoothed average value whichadds to or subtracts from the bias voltage or current andis unlike the signal feedback voltage which variesinstantaneously with the signal at the point from whichit is derived. See also, Bias, Bias Voltage or Bias Cur-rent.

CASCADE AMPLIFIER

A series of amplifiers wherein the input for each ampli-fier except the first (to which the electric signal source isconnected) is coupled from the output of the prioramplifier.

CATHODE OR CATHODE ELECTRODE

The negative electrode of the two electrodes of an elec-tronic tube between which an electric discharge occurs(for negative charge carrier particles); in a vacuum tube

the electrode which emits the electrons and is negativelycharged with respect to the electrode which collects theelectrons.

CATHODE-HEATER

A filament in proximity to an indirectly heated cathodewith terminals designed to receive a source of power toheat the cathode to its electron emitting temperature.

CATHODE IMPEDANCE

The impedance from the cathode of an electronic tube toground or a reference potential.

CHARGE CARRIER PARTICLE

A charged particle of matter involved in a flow of spacecurrent (electric discharge) and by means of which suchcurrent flows (current flow other than an electromag-netic wave propagated in open or confined space). Suchcharge carrier particles may be ions of a gas or chargedatomic particles such as electrons.

COLLECTOR ELECTRODE

See the definition of point contact or junction type tran-sistor below.

COMPRESSOR OR VOLUME COMPRESSOR

A device that compresses the volume range, as inrecording sound, radio-telephone transmission, etc.. Incompressing the signal volume range the amplificationof large signals is reduced and of small signals isincreased.

CONFIGURATION

The arrangement of electrodes of a transistor as inputand output electrodes, e.g., common base configuration,where the base is included in both the input and outputcircuits of a transistor amplifier.

CONTROL

A selective adjustment of an element of an amplifier tovary the operation of the amplifier in a desired manner,or the characteristic of a part of the amplifier whereby inresponse directly to signal, or by means of a developedvoltage or current in response to the signal, or by a volt-age from some outside source, the impedance character-istics of a circuit element, or the electricalcharacteristics (bias or energizing voltage) of an ampli-


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fying device are automatically altered to change theoperation of the amplifier in a predetermined manner.Such control may be by a nonlinear impedance elementalone in a biasing or power supply circuit. The termcontrol has not been applied in this class, when a nonlin-ear impedance element is in the signal path and affectsthe signal only, without any control from a separate pathbeing applied to vary such impedance.

CONTROL ELECTRODE

An electrode designed to influence or control the dis-charge current flowing between other electrodes. It maydepend for its effect on either its electrostatic effect oron the current flow thereto. The most common types ofcontrol electrodes are the signal control grid, or the gaincontrol electrode or grid.

CONCENTRIC LINES

A transmission line in which one conductor extendswithin a second hollow conductor.

CONTROL GRID

A control electrode having grid construction.

D.C. COUPLING

A signal coupling network including a D.C.. conductivepath. In a four terminal network such paths must betraced between terminals on the circuits to and fromwhich the coupling is made which vary in voltage withthe signal (this excludes D.C.. paths limited to groundleads or D.C.. shunt paths).

D.C. PATH OR D.C. CONDUCTIVE PATH

A path for current in a network which can conduct D.C..current.

DELAY NETWORK

Networks including significant structure for retardingwave energy a predetermined period of time over arange of frequencies.

DIODE

Refers to any electronic tube, solid element, semicon-ductor, barrier layer device or other current carriermeans limited to two electrodes and without additionalmagnetic or electrostatic means to influence the current

flow, and which has marked unidirectional current char-acteristics.

DIRECTLY HEATED CATHODE OR FILAMEN-TARY CATHODE

A filament designed to have its terminals connected to asource of current, the filament being heated by the cur-rent passing through it and effective to emit electrons,designed to serve as a cathode of an electronic tube asdefined above.

DISCHARGE PATH

The path of the free electrical charge carrier particlesbetween the electrodes of an electronic tube.

DISTRIBUTED PARAMETER CHARACTERISTICS

A conductor or conductive means designed to operate atmicrowave or other high frequencies, so that the con-ductive means exhibits both distributed capacitance anddistributed inductance at such frequencies.

DISTRIBUTED PARAMETERS

When the impedance of a transmission device or line atthe operating frequency or band of frequencies is dueprimarily to the parameters of the device or line itself,and in considering the inductance, capacitance andresistance of the device or line they must be consideredas mixed together and spread out along the device orline rather than being considered as in separate discretelumps or devices as in the case of simple series and par-allel circuits, the transmission device or line may be saidto have distributed parameters. Examples of circuitswith distributed parameters include telephone, telegraphand power lines for high frequency energy.

DONOR IMPURITY OR DONOR

A material which when added to a semiconductor inminute quantities, as an impurity, induces electron con-duction, generally causing the semiconductor to becomeone of “N-type conductivity”.

ELECTRIC CARRIERS OF A TRANSISTOR

Current flow in a transistor may be by negative carriers(electrons) or positive carriers (holes).

ELECTRIC DISCHARGE

The flow of current between two spaced electrodes at


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different potentials or the charge carrier particles con-veying the current from one spaced electrode to theother.

ELECTRIC SIGNAL SOURCE OR SIGNALSOURCE

The source of electrical signal energy to be amplified orthe source of electrical signal energy which controls theelectric power supply applied to the amplifying device.

ELECTRICAL CIRCUIT

An electrical network providing one or more closedpaths.

ELECTRICAL NETWORK OR NETWORK

An arrangement of electrically connected electrical ele-ments and/or devices which are capable of carryingelectric A.C. or D.C. current. Note. A network does notdefine the structure in space of the network elements ortheir arrangement in space relative to each other; itmerely defines the elements or devices broadly by typeas to the electrical function they perform and the electri-cal connections which will carry current between suchelements and/or devices.

ELECTRODE

(1) In a vacuum tube, electronic tube or in any dis-charge device, the conductive elements between whichthe electric discharge takes place, and to which thepower supply is applied; any additional conductivemeans placed in proximity to the electric discharge and/or other electrodes to affect electrostatically the dis-charge or the potentials of the electrodes with whichthey are in proximity. (2) In a magnetic amplifyingdevice or in a resistive amplifying device, (includingsemiconductive devices) the terminals of windingswhich influence the operation of the magnetic device orthe resistor or semiconductor terminals by means ofwhich electric current may flow in or out of the resistoror semiconductor or by means of which a potential maybe applied to the resistor or semiconductor.

ELECTROMECHANICAL TRANSDUCER

Means to convert the electric signal to mechanicalvibrations and means further to convert the mechanicalvibrations back to electric signals, such means generallyserving as either time or phase delay means or means todetermine the transmission frequency of the couplingnetwork.

ELECTRONIC TUBE

An electric space discharge device, that is, a device inwhich electricity flows from one electrode to another bymeans of free electrical charge carrier particles travelingin a vacuum, gas or vapor; included are electric spacedischarge devices (also called electronic tubes) whichoperate in the open, i.e., not in an enclosed envelope.The electrical charge carrier particles may be of anytype, usually electrons for vacuum tubes or charged ionsfor gas or vapor tubes.

EMITTER ELECTRODE

See the definition of point contact or junction type tran-sistor in this Glossary.

EQUALIZER

Networks with attenuation or attenuation and phase dis-tortion characteristics which vary over a frequencyrange for use in a wave transmission system for modify-ing the attenuation or attenuation and phase characteris-tics of the wave energy as a function of frequency.

EXPANDER OR VOLUME EXPANDER

A device that expands the volume range, as in recordingsound, radio-telephone transmission, etc. In expandingthe signal volume range, the amplification of large sig-nals is increased, and the amplification of small signalsis reduced. Expanders are used generally to restore asignal after compression.

GRID

Is used in the conventional sense referring to theintended use and structure of the element in an elec-tronic tube, particularly in a vacuum tube.

FILAMENT

A wire, ribbon, or rod conductive member.

FILTER

A frequency selective means.

FREQUENCY RESPONSIVE MEANS

Circuit means which acts on the signal to affect somefrequency component of the signal differently from anyother frequency components of the signal, for example,


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a tuned circuit or filter circuit which eliminates a fre-quency component, or an equalizer which emphasizesthe signal amplitude of some frequency or frequencyrange of the signal with respect to others (e.g., tone con-trol). See also, Frequency Selective Means, below.

FREQUENCY SELECTIVE MEANS

Network means composed of some reactive elementswhich permit the passage of certain frequency compo-nents or a frequency component and block others. Seealso, Frequency Responsive Means.

GAIN

The ratio of the amplifier output power, voltage, or cur-rent to the amplifier input power, voltage or current.

GAIN CONTROL ELECTRODE

An electrode designed, together with the electron tube inwhich it is incorporated, to receive a D.C.. control volt-age (other than the signal but which is usually derivedfrom the signal), whereby changes in the control voltagechange the gain of the tube.

GAS OR VAPOR TUBE

An electric discharge device which depends, for itsoperation, at least in part, upon ionization of a gas orvapor.

GRID OR GRID ELECTRODE

An electrode having one or more apertures therein, usu-ally formed of open-work material such as wire mesh,etc.., and usually used as the signal or control electrode,or auxiliary electrode of an electron tube.

IMPEDANCE MATCHING NETWORK

Coupling networks which include one or more imped-ance elements construed or proportioned to substantiallyeliminate the reflected wave energy between the net-work and at least one of the connected circuits causedby impedance differences.

INDIRECTLY HEATED CATHODE (EQUIPTEN-TIAL CATHODE)

A cathode designed to be heated to its emitting tempera-ture by a separate heating element.

INPUT CIRCUIT OR COUPLING

The circuit or network of an amplifier extending fromthe source of electrical signal to the input electrodes ofthe amplifier, which may include the source of electricalsignal.

INTERELECTRODE CAPACITANCE

The capacitive reactance for signal flow between anytwo electrodes of a vacuum tube, transistor or similardevice inherent in their relationship to each other elec-trostatically and which for certain frequencies and volt-ages forms a path for the signal current usuallydetrimental to the operation of the circuit.

INTERELECTRODE IMPEDANCE

An impedance between electrodes of a vacuum tube,transistor, or similar device inherent in its structure, andmanner and frequency of operation. This term isgeneric to inter-electrode capacitance above; andincludes also input conductance caused by the transittime of electrons, etc.

INTERSTAGE CIRCUIT OR COUPLING

The electrical circuit or network by means of which theoutput signal from the output electrodes of the amplify-ing device of one stage of a cascaded amplifier is con-veyed to the input electrodes of the amplifying device ofthe following stage of the cascade amplifier.

INTRINSIC CONDUCTIVITY

Refers to a semiconductor material which for a certainrange of conditions has its free electron carriers and freehole carriers in approximate balance, so that the semi-conductor material is neither N- nor P-type. Sufficientchange in temperature or sufficient radiant energyimpinging upon such a body will upset this equilibrium.

JUNCTION IN A TRANSISTOR OR SEMI-CON-DUCTOR

The boundary of P-type and N-type semiconductormaterial.

JUNCTION TRANSISTOR

A transistor comprising two P-N Junctions back-to-backwherein a region of P- or N-type semiconductor mate-rial is common to both junctions (thus determining anNPN or a PNP junction transistor, respectively); anemitter electrode connected to one of the conductivity


April 2009

regions not common to the two junctions, normally for-wardly biased (positive terminal of bias means to emit-ter for PNP type and negative terminal for NPN type); acollector electrode connected to the other conductivityregion but common to the two junctions, reverselybiased (negative terminal of bias means for the PNPtype and positive terminal for the NPN type; and a baseelectrode connected to the region common to both junc-tions. See definition of Point Contact Transistor, whichoperates similarly in many respects.

LECHER LINES

A parallel transmission line with means to tune the par-allel line.

LOAD

The electric device or circuit which utilizes the outputsignal derived from the amplifier after the input signalhas controlled the electric power supply by means of theamplifying device to yield a signal which is a replica ofthe input signal but usually of greater amplitude.

LONG LINE

A wave transmission device or line having distributedparameters and especially designed to propagate electri-cal wave energy where the wave length of the transmit-ted energy is relatively short when compared with thelength of the transmission line or device. The imped-ance of a long line is practically fixed by the constantsof the line itself. The length of the transmission line ordevice may be a multiple or a fraction of a wave length,e.g., 1/4, 1/2, etc., or otherwise have its length propor-tioned to the wave length of the energy with which it isto be used.

LONG LINE ELEMENT

A circuit element having distributed parameters, such asa resonator, or a wave guide. A long line element maybe a part of a long line wave transmission device or usedin a network with other circuit elements of the lumpedparameter type, for example, as in the case of delay net-works, impedance matching networks, wave filters.

LOOP PATH

In an amplifier having signal feedback, the path of thesignal from the input point where the signal feedback isapplied forward through the amplifier to the point in thecircuit from which the signal feedback is derived

through the signal feedback path to the aforesaid inputpoint.

MAJORITY CARRIERS

See the definition of N- or P-type conductivity below.

MINORITY CARRIERS

See the definition of N- or P-type conductivity below.

NEGATIVE FEEDBACK

Signal feedback having at least some component thereofin opposite phase with the signal at the point where thesignal feedback is applied.

N-TYPE CONDUCTIVITY

The characteristic of a semiconductor material, usuallyimparted by the addition of impurities of the “donor”type, of an excess of free electrons over holes (free posi-tive charges) at any time at room temperature, such neg-ative charge carriers or electrons being referred to asmajority carriers for current flow in such material, andholes as minority carriers for such current flow.

NEUTRALIZATION MEANS

Circuit means to eliminate, mitigate, or lessen undesir-able effects of inter-electrode capacitance or inter-elec-trode impedance and which may include the input and/or output impedance of the amplifying device involved(such input or output impedance includes the inter-elec-trode impedance of the input or output electrodes).

NONLINEAR IMPEDANCE OR DEVICE

An impedance or device, which may be reactive orresistive or a combination of both and having the char-acteristic that for changes in voltage or current, the rela-tionship of the voltage drop across the impedance ordevice, or the voltage applied across the impedance ordevice to the current flowing through it, is nonlinear.

OUTPUT CIRCUIT OR COUPLING

The circuit or network of an amplifier extending fromthe output electrodes of the amplifier to the load device,which may include the load.

PARASITIC REACTANCE, IMPEDANCE, CAPACI-TANCE, OR INDUCTANCE


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Impedance characteristics of capacitive or inductivenature which are exhibited by conductive elements orconductive parts of a circuit at only high frequencies ina circuit designed for operation over a wide band andare inherent in the construction of such element or part.The presence of such reactances is undesirable and gen-erally detrimental to the proper operation of the circuit.When a parasitic reactance is used as though it were apredetermined lumped reactance as in the case of thedistributed capacitance of a coil being used to resonatetherewith at a particular frequency; the distributedcapacitance or other parasitic reactance is treated, forclassification purposes, as though it were a predeter-mined lumped reactance in the circuit. Inter-electrodecapacitances similarly involved in amplifiers as part of atuned circuit are similarly treated.

PASSIVE NETWORK

A network containing no source of energy and in whichno energy is dissipated other than that accounted for bythe resistance of the components of the network.

PHASE SHIFT

Used to designate the change in phase relation betweenvoltage and current of the same wave energy, orbetween the voltages or the currents of different waveenergy of the same frequency.

POSITIVE FEEDBACK

Signal feedback having at least some component thereofin phase with the signal at the point in the amplifier cir-cuit where the signal feedback is applied.

POTENTIOMETER

A network which permits the division of a voltageapplied across it, including adjustable means to select aparticular division of the voltage applied across the net-work.

POWER SUPPLY

The source of electrical energy applied to an amplifyingdevice which is controlled by the electric input signal.The term is used herein generically to include also acathode heater supply, and bias voltage or current sup-ply.

PLURAL AMPLIFIER CHANNELS

An amplifier system having at least two signal channelseach containing separate amplifiers as defined above(wherein each amplifier may be a cascade amplifier),such amplifier channels may be completely separatefrom each other having separate and independentsources or loads; usually with some common control orthey may be in parallel, having a common source and acommon load; or the plural channels may be inbranched circuits from separate sources or to separateloads.

POINT CONTACT TRANSISTOR

A transistor comprising a body of P- or N-type semicon-ductor material to which are attached two closely spacedelectrodes connected at sharply defined points to thesemiconductor material and a third electrode, the baserelatively remote from the other electrodes and having arelatively large contact area (low resistance) for connec-tion to the semiconductor. In this type of transistor theemitter is forwardly biased having, in N-type semicon-ductor material, the positive terminal of the biasingmeans connected to the emitter electrode, and for P-typesemiconductor material the negative terminal of thebiasing means connected to the emitter relative to thebase, to inject minority carriers for the conductivity typesemiconductor material (holes for N-type and electronsfor the P-type) and the collector is biased reversely(having the negative terminal of the biasing means con-nected to the collector for N-type material and the posi-tive terminal for P-type material), relative to the base sothat minority carriers are collected there.

P-TYPE CONDUCTIVITY

The characteristic of a semiconductor material, usuallyimparted by “acceptor” type impurities therein, of anexcess of free positive carriers (holes) over free negativecarriers (electrons), such positive carriers or holes beingreferred to as majority carriers for current flow in suchmaterial and the electrons as minority carriers for suchcurrent flow.

PUSH-PULL STAGE

Includes two amplifiers each as defined above under“AMPLIFIER”, the input electrodes of each of theamplifying devices of the two amplifiers being balancedto ground or some other convenient electrical referenceplane, the source of electrical signal being such, and socoupled to the input electrodes, that at any instant thesignal on each input electrode is substantially equal andopposite in sign to the signal on the other input elec-


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trode; and wherein the signal on the output electrodes ofeach of the amplifying devices is similarly balanced to aconvenient electrical reference plane.

(1) Note. A balanced signal circuit is treated inthis class as a special case of a single sourceor a single load. See Balanced Circuit.

(2) Note. A push-pull amplifier is treated inthis class as a single channel, having a sin-gle source and a single load.

REACTIVE COUPLING

A coupling network including reactive means whichmay be inductive or capacitive.

RECTIFIER

A device with a unilateral current characteristic whichpermits the passage of only D.C. current therethrough,and which is used to convert A.C. current appliedthereto to D.C. current.

RESONANT CIRCUIT

A circuit containing both inductive and capacitive reac-tance and in which the inductive reactance equals thecapacitive reactance for a particular frequency. The res-onant circuit may be series resonant, where the reactiveelements are in series; or parallel (anti-resonant), wherethe inductive and capacitive elements are in parallel.See also, Resonator.

RESONATOR

Devices comprising conductive enclosures, cavities, orwave transmission line sections of the two terminaltype, and having distributed inductance and capacitance,the line sections being terminated in other than the char-acteristic impedance of the line sections, the devicespresenting resonant characteristics to the existing sourceof wave energy. See also Resonant Circuit.

SATURABLE REACTOR

An inductive device having a core and at least one wind-ing thereon in which the inductance is variable in accor-dance with magnetomotive force applied, up to alimiting value beyond which increased magnetomotiveforce does not change the inductance.

SCREEN GRID

A grid electrode placed between the control grid and theanode of a vacuum tube to reduce inter-electrode capac-itance.

SECONDARY EMISSION ELECTRONIC OR VAC-UUM TUBE

A tube which depends for its operation, at least in part,upon the emission of electrons from a body due to colli-sion of higher energy electrons with the body.

SECONDARY EMISSIVE ELECTRODE

An electrode which emits electrons upon collision withhigher energy electrons. Since all electrodes have thischaracteristic, the term applies only to those electrodesdesigned to have an electron stream or beam impingethereon to emit a stream or beam of secondary electrons.

SEMICONDUCTOR

A material having a specific resistance value of theorder of that of germanium, silicon, selenium, etc.; orinsulators whose specific resistance is reduced in valueto the aforesaid range in operation, by alpha particle orelectron bombardment or other means, so that the insu-lators operate broadly as semiconductors in an electricalcircuit.

SEMICONDUCTOR AMPLIFYING DEVICE

An amplifying device constructed of a semiconductorwith suitable electrodes for the application of signal cur-rent, power supply energy, and for the derivation of out-put signal current.

SIGNAL

A variable electrical current or voltage having character-istic variations in time, which characteristic variationsare transmitted through an electrical network from asource in which the signal originates to a load where thesignal is utilized.

SIGNAL ELECTRODE OR SIGNAL GRID

The electrode to which the signal is applied; in the casewhere such electrode is a grid electrode, the signal grid.

SIGNAL FEEDBACK

The application of a signal derived from an output elec-trode, to an input electrode of an amplifier or a prior


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stage of an amplifier. The input and output electrodes ofthe feedback may be the same or a common electrode aswhere vacuum tube space current flows through anunbypassed cathode impedance to change the potentialon the cathode with respect to the control grid in accor-dance with the signal output. (For the distinctionbetween signal feedback and bias control see the defini-tion thereof, above).

SIGNAL FEEDBACK PATH

Circuit means to apply a portion of the electrical signaloutput of an amplifier to the input of the amplifierinvolving a shared impedance for the input and outputcircuits.

STABILIZATION MEANS

In an amplifier having a tendency to depart from a pre-determined condition of operation, any circuit meansused to maintain such predetermined condition of opera-tion of the amplifier. See the definition of Controlabove.

STRUCTURE

Refers to any details of a circuit element as to the natureor composition of the material or materials of which it ismade, the form or shape of the element or its parts or therelationship in space of such elements or parts or suchcharacteristics of the elements relative to each other.

SWITCH

A device or means for opening or closing an electric cir-cuit.

THERMALLY RESPONSIVE IMPEDANCE

An impedance element whose impedance value isresponsive to the temperature changes therein by reasonof the heat generated by the current flow therethrough,or the ambient temperature of the impedance element, orwhose impedance value may be changed by separateelectrical control means or other heat control means.

TRANSISTOR

An amplifying device comprising a semiconductormaterial to which contact is made by three or more elec-trodes.

UNBALANCED CIRCUIT

A circuit having its conductors electrically unsymmetri-cal with reference to a potential plane. For example, aconcentric line is ordinarily unbalanced, the outer con-ductor being ordinarily connected to ground.

VACUUM TUBE

An enclosed space evacuated of most of its gas whereinan electric discharge takes place between two electrodesone of which emits electrically charged atomic particles,generally electrons and the other electrode collects suchparticles. The vacuum tube has at least one additionalelectrode or other means to control the flow of chargedatomic particles between the emitter electrode and thecollector electrode. The electric discharge of a vacuumtube is normally an electron discharge and any dischargeof ionized particles is normally fortuitous and unin-tended. A vacuum tube is usually involved in a four ter-minal network, the input signal being supplied to twoinput electrodes usually the grid (control) and cathode(electron emitting electrode) and the output circuit nor-mally being comprised of the power supply, the anodeload impedance, the anode, the electron discharge, thecathode impedance, the load and the output couplingmeans. Thus the cathode which is normally present inthe output and input circuits is normally the commonelectrode. Other alternative configurations where theinput and output electrodes are not as above, as forexample, where the anode is a common electrode andthe cathode is the output electrode, are known and pro-vided for in the schedule of this class. The terms for thegrid, cathode and anode electrodes or auxiliary elec-trodes (as defined below) are referred to according tothe predetermined use usually assigned for them regard-less of the alternative circuit arrangements involved.The terms input, output, and common electrodes areused as in these definitions.

WAVE ENERGY

An undulatory disturbance propagated through amedium, (usually periodic in nature), its displacementvarying periodically with respect to time or distance orboth. The wave may be manifested in electrical,mechanical or acoustical form. However, in this classthe term “wave energy” refers only to electrical waveenergy.

WAVE GUIDE

A transmission device designed to propagate electricalwaves having an electric or magnetic field componentextending in the direction of propagation. The wave


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guide may be a hollow dielectric or metal tube, or asolid dielectric rod, the wave energy being propagatedalong the interior of the tube or rod and confined by thewalls of the tube or rod.

WAVE TRANSMISSION DEVICE

Any device which is used to guide or constrain electricalwave energy and to convey the energy from one place toanother. Included are conductors, wave guides, resonantstructures (e.g., cavities, etc.).

SUBCLASSES

1 WITH DIVERSE-TYPE ART DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifier iscombined with other devices or structures hav-ing an added purpose or independent utility,other than to perfect the amplifier, and in whichthe utility of the art device is not destroyed byremoval of the amplifier and which combina-tion is not provided for elsewhere.

(1) Note. An example of art classifiable inthis class and subclass is an amplifiercombined with an automobile accelera-tor pedal to control the volume of theamplifier. The removal of the amplifierdoes not destroy the utility of the accel-erator pedal (as it would in case of aradio receiver which included the ampli-fier or a part thereof).

(2) Note. Subject matter in which a sourceis claimed by name only as a specific artdevice, as for example, a microphone, isclassified with the specific art device andnot with amplifiers. Subject matter, inwhich the signal source device may bebroadly claimed, not by name, but bysome distinctive identifying featurethereof as, where a microphone source isclaimed as a “means for convertingsound signals”, is not classified withamplifiers, but with the distinctive artdevice.

(3) Note. The terms generator or oscillatorin claims, where they appear as sourcesof signal energy without further qualifi-cation except by their electrical charac-teristics such as impedance, reactance,etc., are treated as generalized sources of

signal energy and classification is withamplifiers except where specific detailsof the generator or oscillator areclaimed; in such cases, classification iswith the type of generator claimed orwith oscillators in Class 331.

(4) Note. Where the load is claimed, evenbroadly, or by name only as a specificelectrical art device, as for example, aloudspeaker, classification is not in thisclass, but with the load art deviceclaimed. Where characteristics of theload device are claimed, which are pecu-liar to the disclosed electrical art deviceor to a specific type of electrical artdevice, classification is with the load artdevice established in the claim.

(5) Note. Subject matter wherein generalelectrical characteristics of the load areclaimed, as for example, “a load havinga variable impedance”, is classified inthis class.

2 WITH AMPLIFIER CONDITION INDI-CATING OR TESTING MEANS:This subclass is indented under the class defini-tion. Subject matter involving means or meth-ods of testing amplifiers as set forth in the classdefinition and/or amplifiers as set forth in theclass definition combined with indicatingmeans to show a condition of the amplifier.

(1) Note. Amplifiers combined with a meteror indicating means not involving a con-dition of the amplifier but where theamplifier is merely an instrument infacilitating such indication, are not clas-sified in this class and subclass but in theappropriate subclass of Class 324, Elec-tricity: Measuring and Testing or Class340, Communications: Electrical, unlessthey are specialized for use in the testingof a specific electronic art device inwhich case, classification is generallywith the specific electrical art device.

SEE OR SEARCH CLASS:324, Electricity: Measuring and Testing,

appropriate subclasses for electricalmeasuring and testing. See (1) Note,above.


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340, Communications: Electrical, appro-priate subclasses for systems with sig-nal or alarm indicating meansparticularly subclasses 500+. See (1)Note, above.

3 WITH PLURAL DIVERSE-TYPE AMPLI-FYING DEVICES:This subclass is indented under the class defini-tion. Subject matter including at least twoamplifying devices each of which is of a typedifferent from the other.

(1) Note. When each of the amplifyingdevices is of a type which is classified indifferent subclasses of this class provid-ing for such different types of amplifyingdevices, such as subclass 8 for saturablereactor type and subclass 44 for electronbeam type, classification is in this sub-class. Where the different types ofamplifying devices are types providedfor in coordinate subclasses indentedunder a major genus type, classificationis not in this subclass, but in the appro-priate subclasses indented under sub-class 250. Diverse type vacuum tubeamplifying devices combined in anamplifier are classified in subclass 3when each of the diverse type amplify-ing devices is of a type separately pro-vided for by a subclass in this class, asfor example, a traveling wave typeamplifier classified in subclass 43 and anelectron beam tube amplifying deviceclassified in subclasses 44+. Where dif-ferent types of vacuum tubes areinvolved, only one of which is providedfor by a separate subclass, classificationis not in subclass 3 but in the subclassproviding for an amplifier having anamplifier device of that type. Combina-tions of vacuum tube and gaseous tubeamplifiers are classified herein. Diodevacuum tube amplifiers combined withany other type of vacuum tube amplifier,whether provided for as a separate sub-class or not, are classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:150, for cascaded vacuum tube amplifiers

with amplifier devices having differ-ent characteristics (both amplifying

devices being of the same generaltype).

299+, for transistor amplifiers includingcombined diverse type semiconduc-tors.

310, for plural cascaded stage transistoramplifiers including transistors hav-ing different characteristics.

4 WITH MASER-TYPE AMPLIFYINGDEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice combines (1) a substance having thecharacteristic that certain molecular, atomic, ornuclear particles thereof are capable of excita-tion to a higher energy level; (2) means to raisesuch particles to the higher energy level state;(3) means for applying an electrical signal tothe amplifying device; and (4) means for secur-ing the amplified output therefrom, wherebythe aforementioned excited particles in under-going a change from the higher to a lowerenergy state emit radiation which is released bythe applied electrical signal, thereby to amplifyit.

SEE OR SEARCH CLASS:250, Radiant Energy, subclass 251 for

devices for producing and propagat-ing a unidirectional stream of neutralmolecules or atoms through a vac-uum, usually at thermal velocity andincluding means to excite the mole-cules or atoms at a resonant fre-quency.

324, Electricity: Measuring and Testing, subclasses 300+ for electrical measur-ing and testing means involvingnuclear induction, which refers tooperation on a nuclear resonant prin-ciple similar to that employed inmasers.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous circuits which may utilize amaser type circuit.

331, Oscillators, subclass 94.1 for oscilla-tors of the molecular or particle reso-nant type, e.g., maser type.

332, Modulators, appropriate subclassesfor modulators of the molecular or


April 2009

particle resonant type, e.g., masertype.

333, Wave Transmission Lines and Net-works, subclass 24 for gyrator typewave transmission coupling means,including devices operating on amolecular or nuclear resonant princi-ple similar to that employed inmasers.

359, Opticcal: Systems and Elements, subclasses 333+ for optical or quasi-optical maser-type amplifyingdevices.

4.5 PARAMETRIC AMPLIFIERS:This subclass is indented under the class defini-tion. Subject matter including (1) a nonlinearreactance, (2) means for applying an input sig-nal frequency to said nonlinear reactance, (3)means for effectively applying a pumping fre-quency higher than said signal frequency tosaid nonlinear reactance, and (4) means forabstracting the amplified output therefrom,whereby sum and difference frequencies areproduced, one or both of which (but usually thedifference frequency [called the idler fre-quency] reacting with the pumping frequencyto produce energy at the signal frequencywhich is combined in phase with the input sig-nal.

(1) Note. While the pumping frequency ishigher than the signal frequency, thepumping frequency may be derived froma lower frequency source, for example,as a harmonic of the lower frequencysource.

SEE OR SEARCH THIS CLASS, SUB-CLASS:7, for an amplifier with a capacitive

amplifying device.8, for an amplifier with a saturable reac-

tor type amplifying device.53+, for an amplifier with a distributed

parameter coupling means.

4.6 Traveling wave type:This subclass is indented under subclass 4.5.Subject matter including structure for propa-gating energy of the various frequencies ininteracting relationship with the nonlinear reac-tance.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4, for maser type amplifying devices.5, for solid element wave propagating

devices generally.

SEE OR SEARCH CLASS:307, Electrical Transmission or Intercon-

nections Systems, subclass 424 fornonoptical parametric amplifier fre-quency converters, per se.

332, Modulators, subclasses 117+ or 144+for capacitive frequency or phasemodulators, respectively, and subclass173 for magnetic amplitude modula-tors.

333, Wave Transmission Lines and Net-works, subclasses 138+, for delay net-works.

359, Optical: Systems and Elements, sub-classes 326+ for parametric opticalfrequency translators.

455, Telecommunications, subclasses 313+for receivers with frequency modifi-cation or conversion which may useparametric-type means; and subclass336 for superrangenerative receivers.

4.7 Electron beam device:This subclass is indented under subclass 4.6.Subject matter wherein the propagating struc-ture is an electron beam device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:43+, for travelling wave amplifiers.

SEE OR SEARCH CLASS:315, Electric Lamp and Discharge

Devices: Systems, subclasses 3.5+and 39.3, for miscellaneous travellingwave tube systems.

4.8 Gyromagnetic type (e.g., ferrite):This subclass is indented under subclass 4.5.Subject matter wherein the nonlinear reactanceis of the gyromagnetic type.

(1) Note. The term “gyromagnetic” asapplied to material designates magneti-cally polarized material (e.g., ferrites,garnets, and ionized gases) havingunpaired spin systems which exhibit sig-


1April 2009

nificant precessional motion in anorthogonal R.F. field.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4.6, for travelling wave type amplifiers

involving gyromagnetic nonlinearreactance.

SEE OR SEARCH CLASS:333, Wave Transmission Lines and Net-

works, subclasses 1.1 and 24.1+, forgyromagnetic plural channel systemsand coupling networks respectively.

4.9 Semiconductor type (e.g., with semiconduc-tor diode):This subclass is indented under subclass 4.5.Subject matter wherein the nonlinear reactanceis of the semiconductor type (e.g., a diode).

SEE OR SEARCH THIS CLASS, SUB-CLASS:4.6, for travelling wave type parametric

amplifiers whose nonlinear reactanceis of the semiconductor type.

250+, for semiconductor amplifiers gener-ally.

SEE OR SEARCH CLASS:327, Miscellaneous Active Electrical Non-

linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous nonlinear circuits.

5 WITH SOLID ELEMENT WAVE PROPA-GATING AMPLIFYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice comprises a solid-state element wavepropagating means having associated means,such as a distributed parameter network, forcoupling a signal wave to be amplified to thewave propagating means.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4+, for amplifiers having amplifying

devices of the maser type includingthose with solid element wave propa-gating means.

4.6, for travelling wave type parametricamplifiers which may utilize solid-state wave propagating means.

43, for traveling wave tube amplifiers.45, for amplifiers having amplifier

devices of the electron beam typewhich include an electrode coupled toa cavity resonator.

53+, for amplifiers with distributed param-eter type coupling.

250+, for amplifiers having amplifyingdevices of the semiconductive type.


linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous circuits which may include sub-ject matter similar to the amplifiersclassified in this subclass.

331, Oscillators, subclass 94.1 for oscilla-tors of the laser type which mayinclude solid element wave propagat-ing means.

332, Modulators, appropriate subclassesfor modulators of the laser type whichmay include solid element wave prop-agating means.

333, Wave Transmission Lines and Net-works, appropriate subclasses, partic-ularly subclass 24 for distributedparameter transmission couplingmeans including coupling meansinvolving solid element wave propa-gating means.

372, Coherent Light Generators, appropri-ate subclasses for laser type oscilla-tors.

5.5 Phonon type (e.g., ultrasonic wave propa-gating device):This subclass is indented under subclass 5.Subject matter wherein the solid-state means isadapted to propagate and amplify signal wavesin the form of acoustic, ultrasonic or hyper-sonic elastic waves of the phonon type.

SEE OR SEARCH CLASS:181, Acoustics, subclass .5 for mechanical

travelling wave structures for propa-gating acoustic wave.

307, Electrical Transmission or Intercon-nection Systems, subclass 424 fornonoptical parametric amplifier fre-quency converters which may employacoustic waves (e.g., Raman or Brill-cuin devices).


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310, Electrical Generator or Motor Struc-ture, subclasses 311+ piezoelectricdevices in general which may propa-gate elastic waves of the phonon type.

333, Wave Transmission Lines and Net-works, subclasses 138+ for wavedelay networks and subclasses 187+for wave filters utilizing piezoelelec-tric wave propagating elements.

359, Optical: Systems and Elements, sub-classes 326+ for parametric opticalfrequency translators.

367, Communications, Electrical: Acous-tic Wave Systems and Devices, forcompressional wave systems or trans-ducers which may employ solid ele-ment wave propagating devices of thesonic or supersonic type.

6 WITH HALL EFFECT TYPE MEANS:This subclass is indented under the class defini-tion. Subject matter wherein the amplifierincludes means for applying or varying a mag-netic field, and an electrical resistor subjectedto such field or varying field in such mannerthat the value of the resistance transverse to themagnetic field changes, thus comprising a HallEffect Device; such Hall Effect Device maycomprise the amplifying device, per se, or maybe included as a unilateralizing means (gyrator)to insure unilateral operation of the amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:8, for amplifiers having saturable reactor

amplifying devices.60, for amplifiers having magnetostrictive

means in the amplifying device.62, for amplifiers having a magnetoresis-

tive type amplifying device.63, for amplifiers having a magnetic

means type amplifying device notelsewhere provided for.


linear Devices, Circuits, and Systems, subclass 511 for miscellaneous cir-cuits utilizing a Hall effect type ele-ment.

329, Demodulators, appropriate sub-classes for demodulators including aHall effect element.

333, Wave Transmission Lines and Net-works, subclass 24 for Hall effect typegyrators, and subclasses 213+ for twoterminal negative resistance networks.

338, Electrical Resistors, subclass 32 forelectrical resistors whose resistancevalue changes in response to a mag-netic field including resistors respond-ing in accordance with the Hall effect.

7 WITH CAPACITIVE AMPLIFYINGDEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is a nonlinear capacitor.

(1) Note. A nonlinear capacitor is one inwhich for any frequency, the ratio of thevoltage across the capacitor to the cur-rent flowing through it, is not linear.

(2) Note. To be classified in this class theoutput signal must be a substantial rep-lica of the input signal. Subject matterinvolving nonlinear capacitors in whichthe power supply, which is controlled bythe signal, is A.C. must include filtermeans claimed to eliminate the A.C.power supply from the output signal orclassification is in Class 307, ElectricalTransmission or Interconnection Sys-tems, subclasses 40+. However subjectmatter involving nonlinear capacitoramplifying devices wherein an A.C.,power supply is used and claiming ademodulator will be classified hereineven where the output filter is notclaimed, if the filter is disclosed. It willbe assumed to be part of the claimeddemodulator.

SEE OR SEARCH THIS CLASS, SUB-CLASS:8, for amplifiers having saturable reactor

type amplifying devices.10, for amplifiers of the modulator-

demodulator type.86, for signal feedback amplifiers with

variable impedance controlled by aseparate path.

95, and 110, for signal feedback amplifi-ers with nonlinear impedance means.

143, for amplifiers having a thermallyresponsive impedance.


1April 2009

144+, for amplifiers having a variableimpedance for the signal channel con-trolled by a separate control path.

164, for amplifiers having an electronictube or diode in an interstage couplingmeans.

174, for amplifiers having an electrome-chanical transducer (e.g., piezoelectriccrystal) in an interstage couplingmeans.

183, for amplifiers having a nonlineardevice in an interstage D.C. couplingmeans.

250+, for amplifiers having semiconductortype amplifying devices, particularlysubclass 287.


nection Systems, subclasses 401+ fornonlinear reactor systems.

361, Electricity: Electrical Systems andDevices, subclasses 271+ and 500+for capacitors, per se.

8 WITH SATURABLE REACTOR-TYPEAMPLIFYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is a saturable magnetic core with at leastmeans to apply an electrical signal and an A.C.power supply to at least one winding thereon;the input signal which may be D.C. or A.C. isapplied to the signal winding to control an A.C.power supply applied to the power winding,which may be the same winding or a differentwinding.

(1) Note. To be classified in this class thesignal output of the amplifier must be asubstantial replica of the input signal.Therefore subject matter involving satu-rable reactors without filter means is notclassified in this class with amplifiers,but is classified elsewhere. See theSEarch Class: notes below. Subject mat-ter involving saturable reactors claiminga “demodulator” and disclosing a filtertherewith but not claiming the filter areassumed to claim the filter as part of thedemodulator and are classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:7, for amplifiers having capacitive type

amplifying devices including “satura-ble capacitive reactor” means.

10, for modulator-demodulator typeamplifiers.

60, for amplifiers having magnetostrictivemeans.

62, for amplifiers having magnetoresis-tive type amplifying devices.

63, for amplifiers having magnetic meansamplifying devices.


nection Systems, subclasses 416+ foramplifiers using nonlinear reactorswith a nonlinear output signal.

323, Electricity: Power Supply or Regula-tion Systems, subclasses 249, 302,310, and 329 for saturable inductivereactor circuits to control voltagemagnitude. See (1) Note above.

336, Inductor Devices, subclasses 155+ forthe structure of saturable inductiveregulators of the static type.

361, Electricity: Electrical Systems andDevices, subclass 204 for saturablereactors with electric relay or electro-magnet load.

9 WITH PERIODIC SWITCHING INPUT-OUTPUT (E.G., FOR DRIFT CORREC-TION):This subclass is indented under the class defini-tion. Subject matter including a periodicswitching means common to the input and out-put circuits of the amplifier.

(1) Note. This subclass includes essentiallyfour types of subject matter containing aperiodic switch, as follows:

(a)Where the signal is chopped to getA.C. which is fed to the amplifier andthe amplifier output is chopped to get aD.C. output (this subject matter is thesame as is classified in subclass 10below except that the modulator anddemodulator are of the chopper type).


April 2009

(b)The signal to the main amplifier is notchopped but a portion to another ampli-fier is combined with a signal from theoutput of the first amplifier and the twoare chopped to get an A.C. signal whichis used to develop a corrective signal forthe main amplifier.

(c)The input is compared to the outputby a periodic switch to develop a correc-tion signal, generally for drift correction.

(d)The input and output signal are com-bined and then chopped and put into themain amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:83, for push-pull signal feedback amplifi-

ers having a D.C. feedback path.97, for signal feedback amplifiers having

a D.C. feedback path.121, for push-pull amplifiers having D.C.

interstage coupling.125, for plural amplifiers having a D.C.

and an A.C. channel.159, 161, 163, and 181+, for D.C. coupling

involved in the interstage coupling. 187, and 191, for D.C. input coupling. 194, and 198, for D.C. output coupling.

10 MODULATOR-DEMODULATOR-TYPEAMPLIFIER:This subclass is indented under the class defini-tion. Subject matter including means for mod-ulating the signal, which is usually D.C. or lowfrequency A.C. amplifying means, and meansto restore the original signal, eliminating anycarrier frequency components.

(1) Note. The means for eliminating the car-rier need not be specifically claimed tobe classified in this class if such meansare disclosed. As for example, where ademodulator is claimed alone, and a fil-ter means to eliminate the carrier is dis-closed the filter need not be claimed forclassification herein. The claimeddemodulator will be assumed to includethe filter in such cases.

(2) Note. Where the modulator and demod-ulator are of the chopper type see thesearch notes below.

(3) Note. Including in the “means for modu-lating the signal” are chopper means toconvert the signal to pulsating direct cur-rent or alternating current.

SEE OR SEARCH THIS CLASS, SUB-CLASS:7, for amplifiers having a capacitive type

amplifying device including thosewhich modulate and demodulate thesignal.

8, for amplifiers having saturable reactortype amplifying devices includingthose which modulate and demodulatethe signal.

9, for modulator and demodulator of thechopper type.


subclass 118, for measuring systemsinvolving modulation-demodulation.

329, Demodulators, appropriate sub-classes, for demodulator circuits.

332, Modulators, appropriate subclasses,for modulator circuits.

11 WITH D.C. REINSERTION CIRCUIT:This subclass is indented under the class defini-tion. Subject matter including means to restorea D.C. component to the signal, usually bymeans of a D.C. bias source and a rectifier cir-cuit supplied to the control grid.

SEE OR SEARCH THIS CLASS, SUB-CLASS:140, for control of the input or gain control

electrode including a rectifier in thebias circuit.


linear Devices, Circuits, and Systems, subclasses 306+ for miscellaneouscircuits with amplitude control means.

348, Television, subclasses 691+ for televi-sion systems including D.C. reinser-tion circuits.


1April 2009

41 WITH GAS OR VAPOR TUBE AMPLIFY-ING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice includes electrodes in a gas or vapormedium and which device depends upon ion-ization of a gas or vapor for its operation.

SEE OR SEARCH CLASS:313, Electric Lamp and Discharge Devices,

appropriate subclasses, particularlysubclasses 161, 163, and 567+ for gasor vapor tubes, per se.

315, Electric Lamp and DischargeDevices: Systems, appropriate sub-classes, for circuits including gas orvapor tubes as the ultimate loaddevice.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous electronic tube circuits includ-ing gas or vapor tubes with a controlelectrode, controlled in operation.

42 WITH SECONDARY ELECTRON EMIS-SION TUBE AMPLIFYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is a vacuum tube including a secondaryelectron emissive electrode.


subclasses 103+, 377, 379, 399+, and532+ for vacuum tubes, per se, havingsecondary emissive electrode.

315, Electric Lamp and Discharge Devices,Systems subclasses 5.11+, 11, 12.1,39.63 for circuits including vacuumtubes as load devices having a second-ary emissive electrode.

43 WITH TRAVELING WAVE-TYPE TUBE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is of the vacuum tube type includingmeans for generating an electron stream orbeam, and having additional means therein forpropagating an electromagnetic wave or com-ponent thereof at a velocity reduced from thefree space velocity of the wave and propagatedin proximity of the electron stream or beam,

permitting exchange of energy between theelectrons and the electromagnetic wave.

SEE OR SEARCH THIS CLASS, SUB-CLASS:5, for amplifiers having a solid element

wave propagating amplifying device.


Systems, subclasses 3.5+ and 39.3 fortraveling wave type tubes involved asthe load device in miscellaneous cir-cuits. See the search notes under sub-classes 3.5 and 39.3.

331, Oscillators, subclass 82 for travelingwave tube type oscillators.

44 WITH ELECTRON BEAM TUBE AMPLI-FYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is a vacuum tube provided with meansto form the electric space discharge into arestricted beam or ray, usually pencil-like.

(1) Note. Means to control the electron tra-jectory of the electrons emitted from thecathode (as in magnetrons which areclassified below) is not regarded as anelectron beam forming means requiredfor classification in this and indentedsubclasses.

(2) Note. Subject matter broadly claimingso-called “beam power tubes” are notclassified in this subclass but are classi-fied below in the appropriate subclassfor the circuit involved.

SEE OR SEARCH THIS CLASS, SUB-CLASS:42, for amplifiers having secondary elec-

tron emission tube amplifyingdevices.

43, for amplifiers having traveling wavetype amplifying devices.

47, for magnetrons.308, for amplifiers including an electron

beam forming means and a semicon-ductor element as a target meanstherein.


April 2009


subclasses 364+ for cathode-raytubes, per se. See the search notes ofClass 313.

315, Electric Lamp and DischargeDevices: Systems, subclasses 1+ forcathode-ray tubes with means to sup-ply electric current or potential theretoand/or cathode ray tubes structurallycombined with a circuit element. Seethe search notes of Class 315.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclass 600 for miscellaneous cir-cuits having a particular beam tubestructure.

329, Demodulators, appropriate sub-classes and particularly subclass 368for an amplitude demodulatoremploying an electron dischargedevice of three or more electrodes.

45 Having electrode coupled to cavity resona-tor:This subclass is indented under subclass 44.Subject matter wherein at least one electrode iscoupled to a cavity resonator.

SEE OR SEARCH THIS CLASS, SUB-CLASS:49, for amplifiers having vacuum tube

amplifying devices with distributedparameter characteristics.

56, for amplifiers with cavity resonatorcoupling means generally.

SEE OR SEARCH CLASS:331, Oscillators, subclass 83 for multicav-

ity beam tube (Klystron) oscillators.

46 Having deflecting means:This subclass is indented under subclass 44.Subject matter including means to deflect theelectron beam.

SEE OR SEARCH THIS CLASS, SUB-CLASS:41, for amplifiers having gas or vapor

tube amplifying devices includingthose having means to deflect the ion-ized gas or vapor stream.

65, for amplifiers including vacuum tubeamplifying devices having distinctivestructural characteristics or specificstructural details not elsewhere pro-vided for in the schedule.


subclasses 421+ for cathode-raytubes, per se, having electron streamor beam deflecting means.

315, Electric Lamp and DischargeDevices: Systems, subclasses 364+for cathode-ray tubes with means fordeflecting the cathode ray.

47 WITH MAGNETICALLY INFLUENCEDDISCHARGE DEVICE (E.G., MAGNE-TRONS):This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is of the vacuum tube type includingmeans for magnetically influencing the electricdischarge in the device, and not provided forabove.

SEE OR SEARCH THIS CLASS, SUB-CLASS:41, for amplifiers having a gas or vapor

type amplifying device includingthose with magnetic means to deflectthe ionized stream of gas or vapor par-ticles.

42, for amplifiers having secondary emis-sion tube amplifying devices includ-ing those with magnetic means.

43, for traveling wave type tube amplifi-ers which may include magneticmeans.

44+, for electron beam tube amplifyingdevices which may include magneticmeans.


subclasses 153+ for discharge devicecombined with a magnetic device.See the Notes and search notes ofClass 313.

315, Electric Lamp and DischargeDevices: Systems, subclasses 39.51+for magnetrons. See the Notes andsearch Notes and search Notes ofClass 315.


1April 2009

329, Demodulators, subclass 322 for amagnetron type frequency modulatorand subclass 354 for a magnetron typeamplitude modulator.

331, Oscillators, subclasses 86+ for mag-netron oscillators.

48 Having signal applied to magnetic means:This subclass is indented under subclass 47.Subject matter wherein the input signal is cou-pled to the means for magnetically influencingthe electric discharge.

49 WITH VACUUM TUBE HAVING DIS-TRIBUTED PARAMETER IMPEDANCECHARACTERISTICS:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is of the vacuum tube type and includeswithin the vacuum tube an electrode or otherelement having distributed parameter imped-ance characteristics.

(1) Note. Distributed parameter characteris-tics as used in the definition aboveinclude long lines and long line elementssuch as lecher lines, parallel transmis-sion lines in general, concentric lines,wave guides, cavity resonators, tunedtransmission lines, etc., which possessdistributed capacitance and inductance.For the definition of such means, see theclass definition for Class 333, WaveTransmission Lines and Networks.Inherent capacity or inductance as forexample between electrodes or of a leadinside the tube when made use of as alumped reactance circuit element is clas-sified in the appropriate subclass involv-ing the circuit; neutralization byfeedback is classified in subclasses 76+below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4, for amplifiers having a maser type

amplifying device which may includedistributed parameter impedancestructure.

5, for amplifiers having a solid elementwave propagating amplifier device.

43, for amplifiers including travelingwave tubes.

45, for amplifiers of the type having anelectron beam tube amplifying devicewith an electrode coupled to a cavityresonator.

53+, for amplifiers with distributed param-eter type coupling. See the searchnotes thereunder.


Devices: Systems, subclasses 39+ fora vacuum tube combined with distrib-uted parameter type transmissionmeans structure, with the tube as theload device. See the notes and searchnotes thereunder.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclass 593 for miscellaneous cir-cuits with distributed parameters.

359, Optical: Systems and Elements, sub-classes 333+ for laser amplifiers.

50 WITH DUMMY TUBE:This subclass is indented under the class defini-tion. Subject matter including in addition tothe amplifying device of the vacuum tube type,a similar vacuum tube, with the cathodeunheated, so that the additional tube does notserve as an active element but merely presentsimpedance relations in the circuit similar tothose of the amplifying device vacuum tube,usually for neutralizing the effects of theamplifying device interelectrode impedances.

SEE OR SEARCH THIS CLASS, SUB-CLASS:76+, for amplifiers having signal feedback

means to compensate for inter-elec-trode impedance. See the notes andsearch notes thereunder.

51 COMBINED WITH AUTOMATICAMPLIFIER DISABLING SWITCHMEANS:This subclass is indented under the class defini-tion. Subject matter combined with switchmeans, which may be of the electromechanicalor electronic tube type (vacuum, gas, or vaportubes), to disable or discontinue the operationof the amplifier automatically in response to apredetermined condition.


April 2009

(1) Note. Miscellaneous gating circuits areclassified in Class 327, MiscellaneousActive Electrical Nonlinear Devices,Circuits, and Systems, subclasses 365+unless significant details of an amplifieras classified in the class definition of thisclass are claimed when classification isin this class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65+, for specific structure involved in the

amplifier including structure involv-ing switching means.

127+, for amplifiers having means to controlpower supply or bias voltage.

SEE OR SEARCH CLASS:200, Electricity: Circuit Makers and

Breakers, appropriate subclasses, forswitches, per se.

307, Electrical Transmission or Intercon-nection Systems, subclasses 112+ forelectrical transmission or interconnec-tion switching systems.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 365+ for miscellaneousgating circuits.

361, Electricity: Electrical Systems andDevices, subclasses 1+ for electricalsystems and devices with safety andprotection means including thoseinvolving disabling switching means;subclasses 139+ for circuits for elec-tric relays.

52 WITH PILOT FREQUENCY CONTROLMEANS:This subclass is indented under the class defini-tion. Subject matter including means for con-trol of the amplifier which may be for controlof the bias of an amplifier device electrode orof a variable impedance for the signal channel,wherein the signal input includes a componentof a particular frequency not involved in thesignal for signal purpose, which is selected bya means in or associated with the amplifier andapplied to the control means or used to developa control voltage applied to the control means.

(1) Note. See the class definition, LinesWith Other Classes and Within This

Class, for other systems utilizing pilotfrequency control.

SEE OR SEARCH THIS CLASS, SUB-CLASS:85, for signal feedback amplifiers having

an amplifier in the feedback path.86, for signal feedback amplifiers having

a variable impedance in the feedbackpath controlled by a separate controlpath.

96, for signal feedback amplifiers com-bined with control of bias of the signalamplifier.

127+, appropriate subclasses, for control ofbias or power supply, particularly sub-classes 130 and 132. See the searchnotes under subclass 127. See also (2)Note under subclass 130.

143, for amplifiers having a thermallyresponsive impedance which may becontrolled by a separate means.

144+, for amplifiers having a variableimpedance which may be controlledby a separate control path.


works, appropriate subclasses forpilot current controlled transmissionline systems, generally. See the noteand search notes.

370, Multiplex Communications, sub-classes 491 and 500 for a multiplex-ing system using pilot control.

53 WITH DISTRIBUTED PARAMETER-TYPE COUPLING MEANS:This subclass is indented under the class defini-tion. Subject matter wherein the signal energyis coupled to or from the amplifying device bymeans including distributed parameter wavetransmission means; or circuit networks oflumped parameters or impedances designed tosimulate the impedance characteristics of dis-tributed parameter wave transmission means.

(1) Note. Distributed parameter transmis-sion means as used in the definitionabove include long lines and long lineelements such as telephone and tele-graph lines, lecher lines, parallel trans-mission lines, in general, concentriclines, wave guides, cavity resonators,


1April 2009

tuned transmission lines, etc., which pos-sess distributed capacitance and induc-tance. For the definition of such meansand “lumped parameter or impedance”means as used above, see the class defi-nition for Class 333, Wave TransmissionLines and Networks. Subject matterinvolving inherent capacity or induc-tance, as for example, between elec-trodes, or of a lead inside a tube whenmade use of as a lumped reactance cir-cuit element, is classified in the appro-priate subclass involving the circuit.Neutralization by feedback is classifiedin subclasses 76+ below.

(2) Note. Subject matter including distrib-uted parameter circuit coupling meanswhen combined with a special type ofamplifying device is classified with thespecial type of device and not in thissubclass. For example, subclass 43, foramplifiers having traveling wave typetubes, which include distributed parame-ter type delay lines, or wave guides.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for amplifiers having plural diverse

type amplifying devices.4, for amplifiers having a maser type

amplifying device.5, for amplifiers which have solid ele-

ment wave propagating amplifyingdevices.

43, for amplifiers having a traveling wavetype tube amplifying device.

45, for electron beam tube amplifyingdevices coupled to a cavity resonator.

49, for amplifiers having an amplifyingdevice of the vacuum tube type hav-ing distributed parameter characteris-tics.

107, for signal feedback amplifiers havingphase shift means in the loop path.

157+, for amplifier interstage coupling. 185+, for amplifier input coupling. 192+, for amplifier output coupling.


Devices: Systems, appropriate sub-classes indented under subclass 3 andsubclass 39 for distributed parameterimpedance devices.

333, Wave Transmission Lines and Net-works, appropriate subclasses for pas-sive distributed impedance devices.See the notes under the class defini-tions and search notes under the perti-nent subclasses of Class 333.

54 Distributed amplifier:This subclass is indented under subclass 53.Subject matter wherein a plurality of amplifierdevices are in a system having a single sourceand load, include a delay line coupling (whichmay be a distributed parameter line, or an arti-ficial line) and wherein the inputs or outputs ofsuch amplifier devices are coupled to suchdelay line means at phase displaced points.

(1) Note. Push-pull amplifiers includingdelay line coupling, per se, are not clas-sified in this subclass but in subclass 55below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:124+, for plural channel amplifiers. See the

notes and search notes thereunder.

55 Push-pull:This subclass is indented under subclass 53.Subject matter including at least one push-pullstage of amplification.

(1) Note. A push-pull stage of amplificationfor this class requires a balanced input totwo tubes and a balanced output there-from; for further details of the definitionof a push-pull stage of amplification seethe class definitions of this class, sectionI.

SEE OR SEARCH THIS CLASS, SUB-CLASS:118+, for push-pull amplifiers generally. See

the notes and search notes thereunder.


April 2009

56 Waveguide, cavity, or concentric line reso-nator:This subclass is indented under subclass 53.Subject matter wherein the distributed parame-ter wave transmission means is of the waveguide, cavity concentric line type and is reso-nant.

SEE OR SEARCH THIS CLASS, SUB-CLASS:45, for electron beam tube amplifying

device coupled to a cavity resonator.94, and 109, for signal feedback amplifi-

ers having frequency responsivemeans in the feedback path.

302+, for semiconductor amplifiers havingfrequency responsive in the signaltransmission path.

SEE OR SEARCH CLASS:331, Oscillators, subclass 83 for multicav-

ity beam tube oscillators (Klystrons).333, Wave Transmission Lines and Net-

works, subclasses 219+ for distrib-uted parameter type resonators. Seethe note and search notes to this sub-class.

57 Artificial line:This subclass is indented under subclass 53.Subject matter wherein there is included as asignal coupling means a circuit network oflumped parameters or impedances, which isdesigned to simulate the impedance character-istics of a distributed parameter wave transmis-sion means.

(1) Note. Distributed parameter transmis-sion means as used in the definitionabove include long lines and long lineelements such as telephone and tele-graph lines, lecher lines, parallel trans-mission lines, in general, concentriclines, wave guides, cavity resonators,tuned transmission lines, etc.., whichpossess distributed capacitance andinductance. For the definition of suchmeans and “lumped parameter or imped-ance” means as used above, see the classdefinition for Class 333, Wave Transmis-sion Lines and Networks. Subject matterinvolving inherent capacity or induc-tance, as for example, between elec-

trodes, or of a lead inside a tube whenmade use of as a lumped reactance cir-cuit element, is classified in the appro-priate subclass involving the circuit.Neutralization by feedback is classifiedin subclasses 76+ below.


works, subclass 23, for passive typeartificial line, per se; and subclasses138+, for delay lines.

58 WITH ROTATING DYNAMOELECTRICAMPLIFYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is provided with a rotating dynamoelec-tric means; and wherein the power supply elec-trical energy source which is controlled, maybe developed by conversion of mechanicalenergy to electrical energy by the motion of thearmature of the dynamoelectric means, the sig-nal current being applied to magnetic fieldmeans of the device, so that a current is gener-ated which varies with the signal current sup-plied; or the rotating dynamoelectric meansmay act as a motor with the signal currentapplied to the rotating means or the fieldmeans, and the rotary motion of the device maybe utilized as a variable resistor means to effecta control of the power supply source.

(1) Note. Subject matter, as defined above,is classified herein where the device isdisclosed as designed to amplify a sig-nal. Where the system is primarily forthe conversion of electrical energy intomechanical energy or vice versa, or is ofgeneral utility, classification is in Class310, Electrical Generator or MotorStructure, or Class 322, Electricity: Sin-gle Generator Systems, as described inthe, SEARCH CLASS, below. Wherethe structure of a dynamoelectricmachine is claimed, alone, classificationis in the appropriate subclass of Class310, Electrical Generator or MotorStructure.

SEE OR SEARCH CLASS:310, Electrical Generator or Motor Struc-

ture, subclasses 10+ and subclassesindented thereunder for the structure


1April 2009

of dynamoelectric machines, per se,especially indented subclasses 139and 151 for the structure of generatorsof the rotary amplifier type.

322, Electricity: Single Generator Sys-tems, appropriate subclasses particu-larly subclass 61 for generators withalternating current excitation and sub-classes 90 and 91+ for rotating ampli-fiers, especially indented subclass 92for such amplifiers of the crossed-field type.

59 HAVING LIGHT-CONTROLLED ORACTIVATED DEVICE (I.E., NOT LIGHTSIGNAL):This subclass is indented under the class defini-tion. Subject matter including means con-trolled by light or activated by light which maybe involved in the amplifying device, per se,used as a control means, or which may beincluded in any other part of the amplifier.

(1) Note. Subject matter wherein light con-trolled or activated means is not a part ofthe amplifier but is combined therewith(as for example, as a photo-electric cellwith light means therein feeding a signalcurrent to a vacuum tube amplifier) isnot classified in this class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:308, for amplifiers having atomic particle

or radiant energy impinging on asemiconductor amplifying device.See the search notes thereunder.

SEE OR SEARCH CLASS:250, Radiant Energy, subclasses 200+,

appropriate subclasses for photocellcircuits. See also the notes and searchnotes under subclass 200.

60 HAVING MAGNETOSTRICTIVE-TYPEAMPLIFYING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice includes magnetostrictive means, thatis, means for cyclically changing the dimen-sions of a body of magnetic material under theinfluence of a cyclically changing magneticfield in proximity to the body of magneticmaterial.

SEE OR SEARCH THIS CLASS, SUB-CLASS:174, for interstage coupling including elec-

tromechanical transducer means (e.g.,piezoelectric crystals). See the searchnotes thereunder.


works, subclasses 148+ and 186+ forelectromechanical transducer delaylines and filters, respectively. See thesearch notes thereunder.

336, Inductor Devices, subclass 20 forinductive devices having magneto-strictive (deformable) cores.

61 WITH RESISTIVE-TYPE AMPLIFYINGDEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice, to which the electric input signal isapplied to control the power supply source ofelectric energy also applied thereto, is a resis-tive means, which may be liquid, solid, or ofgranular construction.

(1) Note. Not included herein, are otherdevices having resistive properties suchas gas tubes, vacuum tubes, etc.

(2) Note. Variable resistors, althoughincluding a sensing means and/or powersupply means, as structure are classifiedin Class 338, Electrical Resistors.Where such subject matter involves aload circuit, classification is herein,when the signal output is “substantially areplica of the signal input”; otherwiseclassification is in the appropriate sub-class of Class 323, Electricity: PowerSupply or Regulation Systems.

SEE OR SEARCH THIS CLASS, SUB-CLASS:250+, for amplifiers with semiconductor

type amplifying devices. See thenotes and search notes thereunder.

SEE OR SEARCH CLASS:323, Electricity: Power Supply or Regula-

tion Systems.


April 2009

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for systemsutilizing variable resistance devices ofthe nonlinear conductor type andwhich systems are not elsewhere clas-sifiable.

338, Electrical Resistors, appropriate sub-classes for the structure of resistors,per se, especially subclass 100. See(1) Note above.

62 Magnetoresistive type:This subclass is indented under subclass 61.Subject matter wherein the amplifying deviceresistive means is of a type whose resistancevalue varies in response to a magnetic field or achange in magnetic field, and includes meansfor applying such magnetic field to the resistivemeans.

SEE OR SEARCH THIS CLASS, SUB-CLASS:6, for amplifiers having Hall Effect type

amplifying devices.60, for amplifiers having magnetostrictive

means.63, for amplifiers having an amplifying

device with magnetic means, gener-ally.


linear Devices, Circuits, and Systems, subclass 511 for miscellaneous cir-cuits using the Hall effect.

338, Electrical Resistors, subclass 32 forelectrical resistors whose resistancevalue changes in response to a mag-netic field or a change in magneticfield.

63 WITH MAGNETIC MEANS AMPLIFY-ING DEVICE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice includes a magnetic means to controlthe power supply energy or is involved in thestructure of the amplifying device in someother manner and which is not provided forabove.

SEE OR SEARCH THIS CLASS, SUB-CLASS:6, for amplifiers including Hall effect

type amplifying devices.41, for amplifiers including gaseous or

vapor type amplifying devices whichmay have magnetic means for deflec-tion or other purposes.

44+, for amplifiers having electron beamtube amplifying devices which mayhave magnetic means for beamdeflection, focusing or other purposes.

47+, for amplifiers having magneticallyinfluenced discharge devices includ-ing magnetrons.

60, for amplifiers having magnetostrictivemeans.

62, for amplifiers having magnetoresis-tive type amplifying devices.

64 WITH SPACE CHARGE GRID TUBE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifyingdevice is of the vacuum tube type having a pos-itively charged grid (with respect to the cath-ode) immediately adjacent the cathode, whichneutralizes the negative space charge of theelectrons emitted from the cathode so that a“virtual cathode” is produced on the side of thespace charge grid on which the anode is situ-ated, said tube having a normally negativelybiased control grid next to the space chargegrid, to which the signal is coupled, and ananode to receive the electrons emitted by thecathode, and which may have additional elec-trodes between the control grid and the anode.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65, for amplifiers including vacuum tubes

of special structural characteristics.199+, for power or bias voltage supply for

amplifiers, see the search notes there-under.


appropriate subclasses, for dischargedevice structure, per se.


1April 2009

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 524+ for miscellaneouselectron tube circuits with spacecharge grid tubes.

329, Demodulators, subclass 368 for anamplitude demodulator using an elec-tron discharge device of three or moreelectrodes.

65 INVOLVING STRUCTURE OTHERTHAN THAT OF TRANSFORMERS PERSE:This subclass is indented under the class defini-tion. Subject matter involving the structure ofany amplifier circuit element, such as resistors,vacuum tubes, etc., with the exception of thestructure of transformer elements, or of thestructural relationships of such elements in theamplifier.

(1) Note. The term structure, herein, refersto the arrangement in space of the partsto the whole of the circuit element or ofthe elements comprising the amplifierwhich includes also the material ofwhich such parts are constructed. Theterm structure is distinguished from cir-cuit or circuit arrangement in that the lat-ter refers to an abstract schematic ofparts identified broadly by their functionin the circuit and arranged according tothe sequence of signal current flow andnot according to actual arrangement inspace, or construction.

(2) Note. Subject matter involving thestructure of transformers is not classifiedin this or indented subclasses but in sub-classes 171, 190, or 197 below.

(3) Note. Subject matter involving thestructure of any amplifying device orassociated therewith, of the types specif-ically provided for above are not classi-fied in this or indented subclasses but inthe appropriate subclasses for thosetypes, above.

SEE OR SEARCH THIS CLASS, SUB-CLASS:53+, for amplifiers having distributed

parameter coupling means including

the structure of such distributedparameter means.

SEE OR SEARCH CLASS:174, Electricity: Conductors and Insula-

tors, for the structure of electricalinsulators and conductors.

200, Electricity: Circuit Makers andBreakers, for the structure of switchesand circuit breakers.

313, Electric Lamp and Discharge Devices, appropriate subclasses for the struc-ture of electric discharge devices(vacuum tubes and gas tubes), per se.

315, Electric Lamp and DischargeDevices: Systems, subclasses 3+ forcombined cathode-ray tube and circuitelement structure, subclasses 32+ forvacuum or gas tubes combined withintegral circuit structure or tempera-ture modifying means structure wherethe tube is the load device.

334, Tuners, appropriate subclasses fortuners, per se.

336, Inductor Devices, appropriate sub-classes for inductor structure.

338, Electrical Resistors, for the structureof resistors and rheostats.

361, Electricity: Electrical Systems andDevices, subclasses 271+ for capaci-tor structure, subclasses 600+ forhousing and mounting assemblieswith plural diverse electrical compo-nents, subclass 679.01 for electronicsystems and devices, subclasses679.02-679.61 for computer relatedhousing or mounting assemblies, andsubclasses 500+ for electrolyticcapacitors.

439, Electrical Connectors, appropriatesubclasses for the structure of electri-cal connectors.

455, Telecommunications, subclasses 130+for radio receiver structure in general;and subclass 351 for portable radioreceivers.

66 With printed circuits:This subclass is indented under subclass 65.Subject matter wherein the capacitive electrodestructure, inductor structure, resistors, conduc-tors, connectors and/or related circuit elementsform a conductive coating on a base. Forexample, such as is produced by printing,


April 2009

spraying, electro-deposition or similar coatingmethod, or by the removal of adherent con-ducting material from an insulating base byetching, grinding, or the like.


tors, subclasses 250+ for preformedpanel circuit arrangement (e.g.,printed circuits).

336, Inductor Devices, subclass 200 forinductor coil structure of the printedcircuit type. See the search notesthereunder.

361, Electricity: Electrical Systems andDevices, subclasses 736+ and 748+for printed circuits of the type used inradios.

439, Electrical Connectors, subclasses 55+for connectors of the preformed panelcircuit (e.g., printed circuit) type.

67 With capacitive structure:This subclass is indented under subclass 65.Subject matter wherein the structure involvedis that of a capacitor or capacitive element ofthe amplifier circuit.

SEE OR SEARCH THIS CLASS, SUB-CLASS:157+, appropriate subclasses thereunder for

interstage coupling circuits involvingcapacitors.

185+, appropriate subclasses for input cou-pling circuits involving capacitors.

192+, appropriate subclasses for output cou-pling circuits involving capacitors.

SEE OR SEARCH CLASS:334, Tuners, appropriate subclasses for

tuned networks for use in waveenergy apparatus and comprisinginductance and capacitance elementsin circuit arrangement to form a reso-nant circuit and in which structure isprovided for adjusting one or both ofthese elements for changing the meanresonant frequency of the circuit.

361, Electricity: Electrical Systems andDevices, subclasses 271+ and 503+for capacitor structure, per se.

68 With shielding means:This subclass is indented under subclass 65.Subject matter wherein the structure is somemeans for shielding at least part of the ampli-fier from external electric or magnetic fields, orsuch structure to protect parts of the devicefrom undesired electric or magnetic fields orig-inating in another part of the device, or suchstructure to prevent the amplifier or a partthereof from emanating undesired electric ormagnetic fields.

SEE OR SEARCH THIS CLASS, SUB-CLASS:170, for shielding involved in interstage

transformers.190, for shielding involved in input trans-

formers.197, for shielding involved in output trans-

formers.


tors, subclasses 32 through 397 formiscellaneous anti-inductive struc-tures, particularly subclasses 350-397for miscellaneous electrical shieldsand screen structures not elsewhereclassifiable. The search notes to sub-classes 32-397 indicate further fieldsof search for anti-inductive andshielding structures.

307, Electrical Transmission or Intercon-nection Systems, subclasses 89+ foranti-inductive means to prevent ormodify the coupling between electri-cal systems, particularly subclass 91,for “shielding means”. See the searchnotes thereunder.

333, Wave Transmission Lines and Net-works, subclass 12 for transmissionline inductive or radiation interferencereduction systems which includeshielding means for the purpose. Seethe search notes thereunder.

334, Tuners, subclass 85 for a tuner havingshielding or housing means.

69 SUM AND DIFFERENCE AMPLIFIERS:This subclass is indented under the class defini-tion. Subject matter including at least twosources of signal voltage which are combinedin the amplifier so that the signal output of the


1April 2009

amplifier is a linear function of the sum or dif-ference of the signal input sources.

(1) Note. Balanced input circuits or bal-anced output circuits are considered sin-gle signal sources or loads in this class.Therefore a balanced to unbalancedamplifier is not classified in this subclassbut in subclass 116 below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:74, for series energized vacuum tube

amplifiers with plural separate signalinputs.

81, for signal feedback amplifiers havingat least one push-pull stage.

116, for amplifiers having balanced-to-unbalanced coupling. See (1) Noteabove.

118+, for amplifiers including a push-pullstage.

124+, for amplifiers with plural amplifierchannels.

147, for amplifiers having plural signalinputs. See the notes and search notesthereunder.

252+, and 295, for semiconductor amplifiershaving plural channels or pluralinputs.

301, for semiconductor amplifiers havingbalanced-to-unbalanced or unbal-anced-to-balanced coupling.

70 ANODE ENERGIZED THROUGH DIS-CHARGE PATH OF CONTROLLED VAC-UUM TUBE:This subclass is indented under the class defini-tion. Subject matter including at least twoamplifying devices of the vacuum tube type,each having at least three electrodes includinga control grid electrode, wherein at least a por-tion of the anode-cathode power supply cur-rent, for one of the amplifying devices, flows inseries from the power supply source throughthe space discharge path of the other amplify-ing device, so that the tubes are series ener-gized (at least in part) from the power supply.

SEE OR SEARCH THIS CLASS, SUB-CLASS:87+, for cathode impedance feedback, par-

ticularly subclass 95.

128, for control means for the anode circuitincluding diode space discharge pathsin such circuits.

202, for anode power supply, generally.See the search notes thereunder.

293, and 310+, for cascaded semiconduc-tor amplifiers series energized forpower.


linear Devices, Circuits, and Systems, subclasses 530+ for miscellaneouselectron tube circuits with a particularsource of power or bias voltage.

329, Demodulators, appropriate sub-classes for a demodulator with partic-ular power supply circuitry.

71 Plural discharge paths traversed by anodesupply:This subclass is indented under subclass 70.Subject matter wherein power supply currentfor one or more vacuum tube amplifyingdevices is supplied through at least two sepa-rate space discharge paths of at least two vac-uum tubes.

(1) Note. Subject matter including separateand distinct groups of pairs of vacuumtubes having separate and distinct seriesenergized space discharge paths is alsoincluded in this subclass.

(2) Note. A series of three or more vacuumtubes arranged in series for power supplywhich comprises a single discharge pathfor the anode power supply is excludedfrom this subclass.

72 Amplifier devices in arms of a bridge:This subclass is indented under subclass 71.Subject matter including two pairs of seriesenergized tubes wherein one tube of each pairis supplied through its space discharge pathwith anode-cathode power supply current fromthe power supply source, and wherein each ofthe four vacuum tubes is arranged in the armsof a Wheatstone bridge.

73 Plural outputs:This subclass is indented under subclass 70.Subject matter including at least two separatesignal output circuits.


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SEE OR SEARCH THIS CLASS, SUB-CLASS:148, for signal amplifiers having plural

separate signal outputs. See the notesand search notes thereunder.

74 Separate signal inputs to series devices:This subclass is indented under subclass 70.Subject matter including at least two separateinput circuits for each of two series energizedvacuum tube amplifying devices.

(1) Note. A balanced (or push-pull) inputcircuit is treated as a single input circuitin this class and not as two separate inputcircuits.

SEE OR SEARCH THIS CLASS, SUB-CLASS:69, for sum and difference amplifiers.147, for amplifiers with plural signal

inputs. See the notes and search notesthereunder.

75 SIGNAL FEEDBACK:This subclass is indented under the class defini-tion. Subject matter wherein signal feedbackcircuit means are provided to superimpose aportion of the electrical signal output energy onthe amplifier input signal.

(1) Note. The above amplifier may be anystage or group of stages of a cascadedamplifier.

(2) Note. The signal feedback of amplifiersclassified in this and indented subclassesis distinguished from the type of feed-back which may be found in amplifiergain control circuits principally in sub-classes 129+ in that the latter involvesthe development from the signal, of aD.C. voltage which is filtered andsmoothed and then applied to an ampli-fier electrode to control the bias thereon;whereas in this and indented subclassesthe feedback voltage which is applied tothe input electrode varies in each instantin the same manner that the signal variesand may be in any phase relationshipwith the input signal (i.e., in phase, 180°out of phase or any other phase anglerelationship).

(3) Note. The term “loop path” as used insome of the indented subclasses refers tothe loop formed by the forward signalpath from the signal input electrode inthe circuit to which the signal feedbackis applied to the output and in additionthe signal feedback path from the signaloutput electrode from which the feed-back is derived to the signal input elec-trode to which the signal feedback isapplied.

(4) Note. In feedback amplifiers there is animpedance shared by the input and out-put circuits which may be a transformer.

SEE OR SEARCH THIS CLASS, SUB-CLASS:291+, for semiconductor amplifiers having

signal feedback.


linear Devices, Circuits, and Systems, subclass 590 for miscellaneous cir-cuits with signal feedback.

329, Demodulators, subclass 319 for feed-back used in frequency demodulationnoise reduction, and subclass 367 forregenerative feedback in an amplitudedemodulator.

331, Oscillators, appropriate subclasses,for oscillator circuits utilizing feed-back.

700, Data Processing: Generic ControlSystems or Specific Applications,appropriate subclasses for data pro-cessing control systems, particularlysubclasses 1 through 89 for closedloop feedback systems.

76 Compensating for inter-electrode imped-ance (e.g., neutralization):This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” are provided from compensat-ing for or nullifying the undesirable feedbackcaused by any inter-electrode impedances of avacuum tube amplifying device.

(1) Note. The undesirable feedback effectsare usually caused by capacitive inter-electrode impedance although the inter-


1April 2009

electrode impedance involved may beinductive or conductive (e.g., resistive).

(2) Note. Neutralization of the effects ofinter-electrode impedances by other thanfeedback means is not specifically pro-vided for in this and indented subclassesbut is classified with the specific circuitmeans involved, as for example, in inputor output coupling, (subclasses 185+ and192+, respectively). Where the inter-electrode impedance is made use of, asfor example, where the input (grid-cath-ode) capacitance is part of the tunedinput circuit classification is in theappropriate subclass considering theinter-electrode capacitance as though itwere a conventional external circuit ele-ment.

(3) Note. Grounded grid amplifiers whichinherently mitigate the effects of inter-electrode capacitances in vacuum tubesare classified in the cathode coupled sub-classes for which see subclasses 186 and193 and the search notes thereunder.

SEE OR SEARCH THIS CLASS, SUB-CLASS:50, for amplifiers having a dummy tube.65+, for the structure of elements of the

amplifier circuit including vacuumtubes but excluding transformers, perse.

292, for semiconductor amplifiers involv-ing compensating feedback for inter-electrode impedance (e.g., neutraliza-tion).

SEE OR SEARCH CLASS:329, Demodulators, subclass 319 for feed-

back used in frequency demodulationnoise reduction, and subclass 367 forregenerative feedback in an amplitudedemodulator.

331, Oscillators, subclasses 175+ for oscil-lator systems wherein the inter-elec-trode impedance of the active elementof the oscillator may be compensatedfor stabilizing the frequency of thegenerated oscillations.

77 At least one push-pull stage:This subclass is indented under subclass 76.Subject matter including at least one push-pullstage of signal amplification.

(1) Note. For the definition of a push-pullstage of amplification see the class defi-nitions, section I.

SEE OR SEARCH THIS CLASS, SUB-CLASS:81+, for feedback amplifiers having at least

one push-pull stage. See the searchnotes thereunder.

118+, for amplifiers including a push-pullstage. See search notes thereunder.See also (1) Note above.

78 To or from electrode common to input andoutput:This subclass is indented under subclass 76.Subject matter wherein the feedback for nulli-fying or mitigating the effects of inter-elec-trode impedance is applied to or from anelectrode common to the input and output cir-cuits of an amplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:87+, for cathode impedance feedback.

(See the search notes thereunder).111, for signal feedback to or from an aux-

iliary grid or to the anode. See thesearch notes thereunder.

79 By transformer feedback:This subclass is indented under subclass 76.Subject matter wherein the signal feedback forcompensating for inter-electrode impedance iscoupled back to the input from the output bymeans of a transformer.

SEE OR SEARCH THIS CLASS, SUB-CLASS:165+, for amplifiers having interstage trans-

former coupling. See the search notesthereunder.

188+, for amplifier input transformer cou-pled circuits. See search notes there-under.

195+, for amplifier output transformer cou-pled networks. See search notesthereunder.


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80 By coil in parallel to and resonating withinter-electrode capacity:This subclass is indented under subclass 76.Subject matter wherein an inter-electrodecapacitance which may be between the gridand cathode or anode and grid is compensatedfor by a feedback circuit including an induc-tance in parallel with such inter-electrodecapacitance (in the feedback path) and resonanttherewith.

SEE OR SEARCH THIS CLASS, SUB-CLASS:109, for amplifiers having frequency

responsive feedback means.

81 At least one push-pull signal stage:This subclass is indented under subclass 75.Subject matter including at least one stage ofpush-pull signal amplification.

(1) Note. For the definition of a stage ofpush-pull amplification see the class def-inition, Glossary.

SEE OR SEARCH THIS CLASS, SUB-CLASS:77, for amplifiers having at least one

push-pull stage and including feed-back means to compensate for inter-electrode impedances.

118, for amplifiers having at least onepush-pull stage. See the search notesthereunder. See also (1) Note above.

82 Positive and negative feedback:This subclass is indented under subclass 81.Subject matter including at least one signalfeedback means wherein the signal feedback atthe amplifier device input means has a compo-nent in phase with the input signal at this pointin the circuit, and at least one signal feedbackmeans wherein the signal feedback at theamplifier device input means has a componentopposite in phase with the input signal at theamplifier input to which such feedback isapplied.

SEE OR SEARCH THIS CLASS, SUB-CLASS:89, for cathode-cathode feedback for cas-

caded adjacent amplifier stages.

93, for combined diverse type feedbackcoupling including positive feedback.

101, for positive and negative in the samepath at different frequencies.

104, for positive and negative feedbackgenerally.

83 Including D.C. path for signal feedback:This subclass is indented under subclass 81.Subject matter wherein the signal feedbackpath from the output electrode of the amplifierdevice from which the signal feedback isderived to the input electrode of the amplifyingdevice to which the signal feedback is appliedhas a D.C. conductive path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:9, for amplifiers having periodic switch-

ing input-output comparison includ-ing those with D.C. conductivefeedback paths.

97, for amplifiers having a D.C. conduc-tive signal feedback path.

84 Plural amplifier channels:This subclass is indented under subclass 75.Subject matter involving plural amplifier chan-nels combined in addition, for one or morechannels, with signal feedback means above.

(1) Note. Subject matter wherein the signalfeedback is derived from the signal out-put of one amplifier signal channel andapplied to the signal input of anotheramplifier signal channel, is classified inthis subclass.

(2) Note. For the definition of plural ampli-fier channels see subclass 124 below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:124+, for amplifiers with plural amplifier

channels. See the notes and searchnotes thereunder.

85 Amplifier in signal feedback path:This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” has an amplifier therein, asdefined in the class definition, which may havebias control means.


1April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:86, for amplifiers having a variable

impedance in a signal feedback pathvaried by a separate control path.

96, for amplifiers having signal feedbackcombined with means to control thebias of an electrode in the signalamplifier.

129+, for amplifiers having control of theinput electrode or gain control elec-trode bias. See the search notes there-under.

144+, for amplifiers having a variableimpedance for the signal channel con-trolled by a separate control path. Seethe search notes thereunder.

SEE OR SEARCH CLASS:329, Demodulators, subclass 319 for feed-

back used in frequency demodulationnoise reduction, and subclass 367 forregenerative feedback in an amplitudedemodulator.

86 Variable impedance in feedback path variedby separate control path:This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” has a variable impedancetherein, which is varied by means of a controlwhich may be a variable control voltage or amotor control means, the control to vary thevariable impedance being derived, developedand applied by a path separate from thatinvolving the variable impedance and theimmediately associated signal transmissionpath.

(1) Note. This subclass excludes “nonlin-ear” or other impedances in the signalfeedback path which vary merely by thesignal feedback current flow there-through and which are not provided witha “separate” means to control the vari-able impedance. Such subject matter isclassified in subclasses 95 and 110 ofthis class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:143, for amplifiers having a thermally

responsive impedance which may beseparately controlled.

144+, for amplifiers having a variableimpedance for the signal channel var-ied by a separate control path. See thesearch notes thereunder.

87 Cathode impedance feedback:This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” or the “shared impedance of theinput and output circuits” or a portion thereof isan impedance between the cathode of a vac-uum tube amplifying device and ground orother convenient electrical potential referenceplane.

(1) Note. For this and indented subclassesthe anode current flowing through the“cathode impedance” develops a vari-able signal potential on the cathodewhich, relative to the grid of the sameamplifying device is effective as a nega-tive signal feedback in that amplifyingdevice; and which may in addition beapplied as a signal feedback from suchcathode impedance to another input elec-trode of the same amplifying device (oran amplifying device of a precedingstage); or to which cathode impedance asignal feedback may be applied from anoutput electrode of the same amplifyingstage or a following signal amplifyingstage.

(2) Note. Subject matter involving cathodecoupling, such as cathode follower out-put circuits or where coupling is to thecathode and there is normally no cathodeimpedance signal feedback as in “boot-strap” coupling (subclass 156, below) orwhere no signal feedback function isindicated, is not classified in this andindented subclasses but in the appropri-ate cathode coupling subclasses belowsuch as subclasses 186+, for input circuitnetwork coupling to the cathode andsubclasses 193+, for output circuit cou-pling from the cathode. See the internalsearch notes under these subclasses for


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other subclasses of this class involvingcathode coupling.

(3) Note. The above requirement of (2)Note, for classification in this andindented subclasses, namely, that wherecathode coupling is involved an indica-tion that signal feedback is present in thecircuit, applies to all of these subclassesexcept subclass 89 involving cathodeimpedance feedback between adjacentstages. Where there is cathode-to-cath-ode coupling of adjacent cascaded stagesclassification is in subclass 89 regardlessof whether signal feedback is indicatedor not.

(4) Note. Subject matter involving a cath-ode impedance which does not develop asignal feedback voltage but is by-passedin such manner that a D.C.. bias voltageis developed, or due to operating condi-tions, is disclosed, in the case of a singleby-passed resistor, as developing a D.C.bias there across and not a voltage vary-ing with the signal, are not classified inthis and indented subclasses but in sub-class 142 below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for vacuum tube amplifying device

amplifiers series energized for power.78, for signal feedback circuits compen-

sating for inter-electrode impedancesto or from a common electrode.

119, for push-pull amplifiers involvingcathode coupling.

158+, for interstage coupling to the cathode.168, for transformer interstage coupling

from the cathode.172+, for interstage coupling from the cath-

ode.186+, for input coupling to the cathode.193+, for output coupling from the cathode.291+, for semiconductor amplifiers having

signal feedback means.297, for semiconductor amplifiers series

energized for power.

88 Cascade amplifier stages with cathode-cath-ode feedback:This subclass is indented under subclass 87.Subject matter involving at least two stages ofamplification wherein the output of each stageis coupled to the input of the preceding stageexcept the first, and wherein at least two of thestages are arranged as defined in subclass 87with signal feedback from the cathode imped-ance of the latter of the cascaded stages to thecathode impedance of a preceding stage.

SEE OR SEARCH THIS CLASS, SUB-CLASS:92, for signal feedback to the cathode

impedance of a prior stage combinedwith diverse type signal feedback.

98+, for signal feedback in cascaded ampli-fiers generally.

89 Between adjacent stages:This subclass is indented under subclass 88.Subject matter wherein the cathode-cathodefeedback is between adjacent stages.

(1) Note. Where there is cathode-to-cathodecoupling of adjacent cascaded stagesclassification is in subclass 89 regardlessof whether signal feedback is indicatedor not.

90 Combined with diverse-type feedback cou-pling:This subclass is indented under subclass 87.Subject matter combined with a type of signalfeedback as defined in subclass 75, which isdiverse from the type of feedback defined insubclass 87.

91 Diverse feedback to or from cathode:This subclass is indented under subclass 90.Subject matter wherein the diverse signal feed-back is derived from the cathode feedbackimpedance and fed to the input electrode of thesame or a prior stage; or wherein the diversesignal feedback is derived from an output elec-trode of the same or a following stage andapplied to the cathode impedance.


1April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:78, for signal feedback to or from a com-

mon electrode compensating for inter-electrode impedance.

92 Feedback to cathode impedance of a priorstage:This subclass is indented under subclass 91.Subject matter wherein the diverse signal feed-back is derived from an electrode other than thecathode and applied to the cathode impedanceof a prior stage whereby the diverse signalfeedback path includes or overlaps the cathodeimpedance feedback path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:100, for amplifiers having multiple signal

feedback paths in general, includingsignal feedback to the input of a priorstage.

93 Including positive feedback:This subclass is indented under subclass 90.Subject matter including a signal feedbackmeans whereby the feedback has a componentin phase with the signal applied at the inputelectrode to which the signal feedback isapplied.

SEE OR SEARCH THIS CLASS, SUB-CLASS:82, for push-pull amplifiers having posi-

tive and negative feedback.89, for cathode-to-cathode feedback

between adjacent stages.101, for positive and negative feedbacks in

the same path at different frequencies.104, for positive and negative feedback,

generally.112, for positive feedback, generally.

SEE OR SEARCH CLASS:329, Demodulators, subclass 367 for an

amplitude demodulator utilizingregenerative feedback.

331, Oscillators, appropriate subclasses foroscillators operating on the positivefeedback principle.

333, Wave Transmission Lines and Net-works, subclasses 213+ for negativeresistance and/or reactance networks

of the active element type which usu-ally include positive feedback.

455, Telecommunications, subclass 336 forsuperregenerative receivers; and sub-class 337 for regenerative receivers.

94 Frequency responsive means in cathodeimpedance feedback path:This subclass is indented under subclass 87.Subject matter including in the “cathodeimpedance to ground signal feedback path” orin shunt therewith circuit means which acts onthe signal feedback to affect some frequencycomponent of the signal feedback differentlyfrom the other frequency components of thesignal feedback, for example, a tuned circuit orfilter circuit which eliminates a frequency com-ponent, or an equalizer which emphasizes orde-emphasizes the signal feedback amplitudeof some frequency or frequency range of thesignal feedback with respect to others.

SEE OR SEARCH THIS CLASS, SUB-CLASS:107, for amplifiers having phase shift

means in the loop path.109, for amplifiers having frequency

responsive signal feedback means.


works, subclasses 24+ for passivecoupling networks in general.

95 Nonlinear impedance means in cathodeimpedance feedback path:This subclass is indented under subclass 87.Subject matter wherein the “cathode imped-ance signal feedback path” has therein a non-linear impedance circuit element, which maybe resistive, capacitive, or inductive, andwhose impedance is such, that the relationshipfor changes in voltage, between the voltageacross the nonlinear element to the current flowtherein is nonlinear.


impedance in the feedback path variedby a separate control path. See thesearch notes thereunder.

110, for amplifiers having a nonlinearimpedance device in the loop path.


April 2009

183, for amplifiers having a D.C. interstagecoupling means including a nonlinearimpedance element. See the searchnotes thereunder.

96 Combined with control of bias voltage of sig-nal amplifier:This subclass is indented under subclass 75.Subject matter combined with bias voltagecontrol means for a signal amplifying device.

(1) Note. For the definition of an amplifierwith bias voltage control see subclass129 below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:129+, for amplifiers having bias voltage

control means. See the search notesthereunder.

97 Including D.C. path for signal feedback:This subclass is indented under subclass 75.Subject matter wherein the signal feedbackpath, from the output electrode of the amplify-ing device from which the signal feedback isderived to the input electrode of the amplifyingdevice to which the signal feedback is applied,is a D.C.. conductive path.


ing means for input-output compari-son including those with D.C.conductive feedback paths.

83, for push-pull amplifiers having D.C.conductive signal feedback paths.

98 In cascade amplifiers:This subclass is indented under subclass 75.Subject matter including at least two stages ofamplification (each as defined in the class defi-nition) wherein the means for coupling theinput signal for each stage except the first iscoupled to the means for coupling the outputsignal of the preceding amplifier; combinedwith signal feedback means above.

SEE OR SEARCH THIS CLASS, SUB-CLASS:88+, for cathode-cathode signal feedback

in cascaded amplifiers.

92, for cascaded amplifiers with signalfeedback to the cathode impedance ofa prior stage.

99 Multiple feedback:This subclass is indented under subclass 98.Subject matter including at least two signalfeedback circuit means as defined therein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:88+, for cascaded amplifiers having cath-

ode-to-cathode signal feedback.90+, for amplifiers having cathode imped-

ance signal feedback combined withdiverse type signal feedback coupling.

100 A feedback to input of a prior stage:This subclass is indented under subclass 99.Subject matter wherein at least one of the sig-nal feedback means has the signal feedbackapplied to the signal input of a prior stage sothat the path of such feedback means extends toinclude all or a portion of at least one other sig-nal feedback means (overlapping feedbacks).


ode-to-cathode signal feedbackmeans.

92, for cascaded amplifiers includingfeedback to the cathode impedance ofa prior stage.

101 Positive and negative feedback in same pathat different frequencies:This subclass is indented under subclass 75.Subject matter wherein a single signal feed-back circuit means through an impedanceshared by the same input and output circuitshas for currents flowing through the sameshared feedback impedance at one frequency asignal feedback in phase (positive feedback)with the signal input where the signal feedbackis applied and at least at some other frequencya signal feedback component flowing throughthe same feedback impedance, in oppositephase with the signal (negative feedback).

SEE OR SEARCH THIS CLASS, SUB-CLASS:82, for amplifiers having at least one

stage of push-pull amplification


1April 2009

including both positive and negativefeedback.

89, for cascaded amplifiers having cath-ode-cathode signal feedback betweenadjacent stages.

93, for amplifiers having cathode imped-ance feedback and positive feedback.

104, for amplifiers having multiple signalfeedbacks including both positive andnegative feedback.

102 Current and voltage feedback:This subclass is indented under subclass 75.Subject matter including signal feedback pro-portional to the current flow through the outputload which receives the amplified signal, andsignal feedback proportional to the voltageacross the output load.

SEE OR SEARCH THIS CLASS, SUB-CLASS:105, for amplifiers with signal feedback

from an impedance in series with theoutput load (e.g., current feedback).

103 Multiple feedback paths:This subclass is indented under subclass 75.Subject matter including two or more signalfeedback circuit means as therein defined andnot previously provided for in this schedule.


ode-cathode signal feedback.90+, for cathode impedance signal feed-

back combined with diverse type sig-nal feedback.

99+, for cascaded amplifiers having multi-ple feedbacks.

102, for amplifiers having current and volt-age feedback.

104 Positive and negative feedback:This subclass is indented under subclass 103.Subject matter including at least one signalfeedback means having a component of the sig-nal feedback in phase with the signal at thepoint in the circuit where the signal is appliedand at least one signal feedback circuit meanshaving a signal feedback component which isin phase opposition with the signal.

SEE OR SEARCH THIS CLASS, SUB-CLASS:82, for push-pull amplifiers having nega-

tive and positive feedback means.89, for cascaded amplifiers having cath-

ode-cathode signal feedback betweenadjacent stages.

93, for cathode impedance feedback com-bined with diverse type feedback cou-pling including positive feedback.

101, for positive and negative feedback inthe same path at different frequencies.

SEE OR SEARCH CLASS:329, Demodulators, subclass 367 for an

amplitude demodulator utilizingregenerative feedback.

331, Oscillators, appropriate subclasses foroscillators operating on the positivefeedback principle.

333, Wave Transmission Lines and Net-works, subclasses 213+ for negativeresistance and/or reactance networksof the active element type which usu-ally include positive feedback.


105 From impedance in series with output load(e.g., current feedback):This subclass is indented under subclass 75.Subject matter wherein the signal feedback isfrom an impedance in series with the outputload which receives the amplified signal,whereby the signal feedback voltage is propor-tional to the current flowing in the output load.

SEE OR SEARCH THIS CLASS, SUB-CLASS:102, for amplifiers having current and volt-

age feedback.

106 In series with input source:This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” is in series with the signal inputsource between the point in the signal circuitfrom which the signal feedback is derived tothe point in the circuit at which the signal feed-back is applied.


April 2009

107 Phase shift means in loop path:This subclass is indented under subclass 75.Subject matter wherein the “loop path” (see (3)Note under subclass 75 for the definition ofloop path) includes voltage or current phaseshift or delay means which may shift the phaseof the voltage or current of one signal fre-quency or signal frequency feedback compo-nent with respect to another or shift the phaseof the voltage of the signal or signal feedbackwith respect to the current.

(1) Note. Transformer or amplifier meanswhich inherently shift the phase 1805 arenot regarded as phase shift or voltagedelay means for this subclass. If suchtransformer or amplifier include addi-tional phase shift means classification isherein.


parameter coupling which mayinclude electric wave delay means.

101, for amplifiers having positive andnegative feedback in the same path atdifferent frequencies.


tion Systems, subclasses 212 through219 for phase control systems in gen-eral.

333, Wave Transmission Lines and Net-works, subclasses 138+ for electricwave delay networks, of the passivetype, see the search notes thereunder.

108 Potentiometer common to signal and feed-back path:This subclass is indented under subclass 75.Subject matter wherein the signal transmissionpath and the “signal feedback circuit means”both include a potentiometer or a part thereofin common.


tion Systems, for voltage magnitudecontrol systems in general, includingresistors.

109 Frequency responsive feedback means:This subclass is indented under subclass 75.Subject matter wherein the “signal feedbackcircuit means” includes circuit means whichacts on the signal feedback to affect some fre-quency component of the signal feedback dif-ferently from the other frequency componentsof the signal, as for example, a tuned circuitwhich eliminates a frequency component of thesignal feedback or an equalizer which empha-sizes or de-emphasizes the amplitude of somefrequency range of the signal feedback withrespect to others.

SEE OR SEARCH THIS CLASS, SUB-CLASS:94, for frequency responsive cathode

impedance feedback means.107, for signal feedback amplifiers includ-

ing phase shift means in the loop pathincluding those involving frequencyresponsive feedback means.


works, subclasses 28 and 167+ forfrequency responsive passive cou-pling networks in general. See thesearch notes thereunder.

110 Nonlinear impedance element in loop path:This subclass is indented under subclass 75.Subject matter wherein the “loop path” (see (3)Note under subclass 75 for the definition ofloop path) includes a nonlinear impedance cir-cuit element, which may be resistive, capaci-tive, or inductive, and whose impedance issuch for changes in voltage applied thereto thatthe relationship between the voltage acrosssuch element to the current flow through theelement is nonlinear.


impedance in the feedback path variedby a separate control path. See thesearch notes thereunder.

95, for amplifiers having a nonlinearimpedance element in the cathodeimpedance feedback path.


1April 2009

143, for amplifiers having a thermallyresponsive impedance in the signalpath.

183, for amplifiers having a D.C. interstagecoupling means including a nonlinearimpedance element. See the searchnotes thereunder.

111 To or from an auxiliary grid or to the anode:This subclass is indented under subclass 75.Subject matter wherein the amplifying deviceor devices involved are of the vacuum tubetype and wherein the signal feedback is derivedfrom an electrode thereof other than the anodeor cathode and/or is applied to an electrodethereof other than the cathode or control grid.

SEE OR SEARCH THIS CLASS, SUB-CLASS:160+, for interstage signal coupling involv-

ing coupling to the screen grid, plate,suppressor grid (and grid other thanthe control grid or cathode). Seesearch notes thereunder.

162+, for interstage signal coupling from agrid (from an electrode other thananode or cathode). See search notesthereunder.

112 Positive feedback:This subclass is indented under subclass 75.Subject matter wherein the signal feedback hasa component in phase with the signal where thefeedback is applied and which is not providedfor above.

SEE OR SEARCH THIS CLASS, SUB-CLASS:82, for push-pull amplifiers including

positive signal feedback.89, for cascaded amplifiers having cath-

ode-cathode signal feedback.93, for cathode impedance signal feed-

back combined with diverse type sig-nal feedback including positive signalfeedback.

101, for positive and negative feedback inthe same path at different frequencies.

104, for positive and negative feedbackscombined, generally.

SEE OR SEARCH CLASS:331, Oscillators, appropriate subclasses for

oscillators operating on the positivefeedback principle.

333, Wave Transmission Lines and Net-works, subclasses 213+ for negativeresistance and/or reactance networksof the active element type which usu-ally include positive feedback.


113 POLYPHASE POWER SUPPLY (I.E., FORAN ELECTRODE, CATHODE HEATER,OR FILAMENT):This subclass is indented under the class defini-tion. Subject matter including a polyphasepower supply for the energizing or bias voltagesupply applied to any electrode or for a fila-ment or for any heater for a cathode electrode.

SEE OR SEARCH THIS CLASS, SUB-CLASS:114+, for amplifiers having unrectified

power supply.199, for amplifiers involving power or bias

voltage supply. See the search notesthereunder.


nection Systems, subclasses 13+ forplural load systems of the polyphasetype.

310, Electrical Generator or Motor Struc-ture, appropriate subclasses undersubclasses 10+ for dynamoelectricmachine structure of the polyphasetype.

323, Electricity: Power Supply or Regula-tion Systems, appropriate subclassesfor systems in which a single sourceof supply is connected to a single loadand the system includes means forcontrolling only the magnitude of thecurrent, the voltage, and/or the phaseangle between the current and thevoltage in the system. The singlesource may be a polyphase source.

336, Inductor Devices, subclasses 5+ forthe structure of polyphase inductordevices.


April 2009

363, Electric Power Conversion Systems,particularly subclasses 148+ for phaseconversion systems from one numberof phases to a different number ofphases.

114 UNRECTIFIED A.C. POWER SUPPLYFOR AN ELECTRODE (I.E., NOT THEHEATER):This subclass is indented under the class defini-tion. Subject matter wherein the source ofelectrical energy which is controlled by theelectrical signal is an A.C. electrical source,which is applied as an A.C. power supplydirectly to an electrode without any interveningrectifiers to rectify the A.C. electrical supply.

(1) Note. Special types of amplifiers areclassified above and subject matterinvolving unrectified A.C. as a powersupply would be classified with the spe-cial type of amplifier and not herein.The amplifiers having general vacuumtube amplifying devices with this featureare classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for vacuum tube amplifying devices

series energized.113, for amplifiers having a polyphase

power supply.199, for amplifiers involving power or bias

voltage supply means, generally. Seealso search notes thereunder.

296, and 297, for semiconductor amplifiersinvolving bias or power supply cir-cuits.

SEE OR SEARCH CLASS:363, Electric Power Conversion Systems,

appropriate subclasses thereunder, forpower supply means combined withmeans to convert A.C. to D.C. or viceversa.

115 Applied to filamentary cathode:This subclass is indented under subclass 114.Subject matter wherein the electrode, to whichthe A.C. power supply voltage is applied, is afilamentary directly heated cathode.

(1) Note. A.C. power supply for heaters ofindirectly heated cathodes are not classi-

fied in this subclass but are classified insubclass 113, above, in the special casewhere they involve a polyphase powersupply. Amplifiers with cathode fila-ments heated by the anode current areclassified in subclass 201 of this class.Amplifiers with heater supply otherwiseare classified in subclass 199.


Devices: Systems, appropriate sub-classes indented under subclass 94,particularly subclasses 97 and 105+for subject matter involving A.C.power supply to cathodes or cathodeheaters.

116 WITH BALANCED-TO-UNBALANCEDCOUPLING:This subclass is indented under the class defini-tion. Subject matter including a circuit in thesignal path in the conductors of which electri-cal signal flows so that at any instant the signalpotential in the conductors is substantiallyequal and opposite in sign with reference toground or some other convenient referencepotential plane; and wherein further, in the sig-nal path there is included a circuit in the con-ductors of which signal flows which isunbalanced to ground comprising a single-sided output load usually of two conductorsone of which is at ground or reference poten-tial.

(1) Note. Subject matter as defined aboveincluding additional unbalanced outputor load circuits as set forth above is alsoclassified in this subclass.

(2) Note. Balanced circuits are consideredas single sources or single loads in thisclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:69, for sum and difference amplifiers.117, for amplifiers having unbalanced to

balanced coupling.118, for amplifiers including a push-pull

stage. See the search notes thereun-der.

301, for semiconductor amplifiers havingbalanced to unbalanced circuits.


1April 2009


linear Devices, Circuits, and Systems, subclass 594 for miscellaneous cir-cuits with particular coupling ordecoupling means.

329, Demodulators, appropriate sub-classes for demodulators with bal-anced to unbalanced coupling.

333, Wave Transmission Lines and Net-works, subclasses 4+ and 25+ for bal-anced to unbalanced passive circuits.See the search notes under subclasses4 and 25.

117 WITH UNBALANCED-TO-BALANCEDCOUPLING:This subclass is indented under the class defini-tion. Subject matter including in the signalpath a circuit electrically unbalanced toground, or a convenient electrical referencepotential plane, from a single source of electri-cal signal and having at some subsequent loca-tion of the signal path, with or without one ormore intervening amplifying devices, a bal-anced circuit wherein at least two of the con-ductors have at any instant electrical signalflowing therethrough substantially equal andopposite in sign with reference to ground orsome other convenient reference plane.

(1) Note. Balanced circuits are treated assingle sources of electrical signal or assingle loads in this class.

(2) Note. Phase splitters are classified inthis subclass. Phase inverter amplifiercircuits are classified in this subclass andsubclass 116 above.

SEE OR SEARCH THIS CLASS, SUB-CLASS:116, for amplifiers having balanced-to-

unbalanced coupling.118, for amplifiers having a push-pull

stage. See the notes and search notesthereunder.

301, for semiconductor amplifiers havingunbalanced to balanced circuits.


linear Devices, Circuits, and Systems, subclass 594 for miscellaneous cir-cuits with particular coupling ordecoupling means.

329, Demodulators, appropriate sub-classes for demodulators with unbal-anced to balanced coupling.

333, Wave Transmission Lines and Net-works, subclasses 4+ and 25+ forunbalanced-to-balanced passive cir-cuits. See the search notes under thesubclasses 4 and 25.

118 INCLUDING A PUSH-PULL STAGE:This subclass is indented under the class defini-tion. Subject matter including two amplifiersas defined in the class definition, the inputelectrodes of each of the amplifying devices ofthe two amplifiers being balanced to ground orsome other convenient electrical referenceplane, the source of electrical signal beingsuch, and so coupled to the input electrodes,that at any instant the signal on each input elec-trode is substantially equal and opposite in signto the signal on the other input electrode; andwherein the signal on the output electrodes ofeach of the amplifying devices is similarly bal-anced to a convenient electrical referenceplane.

(1) Note. A balanced signal circuit is treatedas a special case of a single source or asingle load, in this class.

(2) Note. A push-pull amplifier is treated asa single channel with a single source anda single load in this class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:55, for push-pull amplifiers including a

push-pull stage.69, for sum and difference amplifiers sim-

ilar in structure to push-pull amplifi-ers.

71+, particularly subclass 72, for push-pullamplifiers included in series ener-gized vacuum tube arrangements.

77, for push-pull amplifiers having feed-back compensation to mitigate inter-electrode impedance effects.


April 2009

81+, for amplifiers having at least onepush-pull stage having signal feed-back.

116, for amplifiers with balanced-to-unbal-anced coupling.

117, for amplifiers with unbalanced-to-bal-anced coupling including phase split-ters.

262+, for semiconductor amplifiers includ-ing a push-pull stage.


linear Devices, Circuits, and Systems, subclass 595 for miscellaneous cir-cuits including push pull circuits.

333, Wave Transmission Lines and Net-works, subclasses 4+ and 25+ for pas-sive balanced networks. See thesearch notes under subclasses 4 and25.

119 Coupling to or from cathode in push-pull:This subclass is indented under subclass 118.Subject matter wherein the two amplifyingdevices in push-pull are vacuum tube amplify-ing devices and wherein the input electrodes orthe output electrodes are the cathode electrodesof the vacuum tube amplifying devices.

SEE OR SEARCH THIS CLASS, SUB-CLASS:158+, for amplifiers with interstage coupling

to the cathode of an amplifyingdevice.

168, and 172, for interstage coupling fromthe cathode.

186+, for input coupling to the cathode. Seethe search notes thereunder.

193+, for output coupling from the cathode.See search notes thereunder.

120 Interstage coupling between push-pull:This subclass is indented under subclass 118.Subject matter including at least two cascadedstages of amplification, each stages as definedin subclass 118 above and each stage exceptingthe first having its signal input coupled to thesignal output of the preceding stage involvingspecific details or distinctive characteristics ofthe coupling between the stages.

SEE OR SEARCH THIS CLASS, SUB-CLASS:157+, for interstage coupling. See the

search notes thereunder.

121 D.C. coupling:This subclass is indented under subclass 120.Subject matter wherein the signal couplingpath from the output electrode of each amplify-ing device of the preceding stage to the inputelectrode of the corresponding device of thefollowing stage is a D.C.. conductive path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:159, 161, 163, 172, and 181+, for various

types of interstage D.C. coupling. Seealso the search notes thereunder.

122 Input and/or output coupling for push-pull:This subclass is indented under subclass 118.Subject matter involving specific details or dis-tinctive characteristics of the input and/or out-put circuits coupling the source to theamplifying devices and the amplifying devicesto a load, respectively.

SEE OR SEARCH THIS CLASS, SUB-CLASS:185, for amplifier input networks. See the

notes and search notes thereunder.192, for amplifier output networks. See

the notes and search notes thereunder.

123 Power or bias supply circuits and controlthereof:This subclass is indented under subclass 118.Subject matter including means to control thepower supply and/or bias voltage supplyapplied to the electrodes of the amplifyingdevices; and/or subject matter under subclass118 involving specific details or distinctivecharacteristics of the power or bias voltagesupply of the amplifying devices.

SEE OR SEARCH THIS CLASS, SUB-CLASS:127+, for amplifiers with control of power

supply or bias voltage. See the notesand search notes thereunder.

129+, for amplifiers with control of inputelectrode or gain control electrode


1April 2009

bias. See the notes and search notesthereunder.

199+, for amplifier power or bias supplyvoltages. See the notes and searchnotes thereunder.

124 WITH PLURAL AMPLIFIER CHANNELS(E.G., PARALLEL AMPLIFIER CHAN-NELS):This subclass is indented under the class defini-tion. Amplifier systems wherein there are atleast two signal channels each containing anamplifier as defined in the class definition,(Section I).

(1) Note. For this and indented subclassessuch amplifier channels may be separate;in parallel with a common source and acommon load; or in branched circuitchannels from separate sources or to sep-arate loads.

(2) Note. Sum and difference amplifiersinvolving two or more signal inputs tothe same channel or a different channelwhere the output is proportionally thesum or difference of the plural inputs arenot classified herein. See the searchnotes below.

(3) Note. A balanced circuit is regarded as asingle source or load for the purposes ofclassification in these subclasses. Apush-pull amplifier is regarded as a sin-gle amplifier channel for purposes ofclassification in this class. Balanced cir-cuits and push-pull amplifiers are to befound in this class.

(4) Note. The plural channels need notamplify or operate simultaneously to beclassified herein. Subject matter involv-ing plural channels with switchingmeans to select with alternatively one ormore channels to amplify a signal a clas-sified in this or indented subclasses.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for amplifiers having diverse type

amplifying devices.53, for amplifiers having distributed

parameter coupling.

55, for amplifiers having distributedparameter coupling;

69, for sum and difference amplifiers.See (2) Note above.

70+, for amplifiers with series arrangedamplifier devices.

71+, for series energized amplifier devices; 73, for plural outputs.74, for plural separate signal inputs.77, for push-pull amplifiers with feedback

compensation for the effects of inter-electrode capacitance (e.g., neutraliza-tion).

81+, for signal feedback amplifiers havingat least one push-pull stage.

84, for signal feedback amplifiers withplural amplifier channels.

116, for amplifiers with balanced-to-unbal-anced coupling.

117+, for amplifiers having unbalanced-to-balanced coupling; and subclasses

118+, for amplifiers including a push-pullstage.

147, for amplifiers having plural inputsources.

148, for amplifiers having plural loads.151, for cascaded amplifiers with means to

by-pass a stage.252+, and 295, for plural semiconductor

amplifier channels.262+, 301 for semiconductor amplifiers;


nection Systems, subclasses 11+ and43+ for plural load circuit and supplycircuit systems respectively.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous nonlinear circuits utilizing elec-tron tube or semiconductor devices.

333, Wave Transmission Lines and Net-works, subclasses 1+ for plural chan-nel passive network systems.

381, Electrical Audio Signal Processingand Systems, subclass 77 for pro-gram distribution systems involvingdistribution of a program to a pluralityof local stations where the program isamplified and reproduced.


April 2009

125 D.C. and A.C. amplifier channels:This subclass is indented under subclass 124.Subject matter wherein at least one of the sig-nal channels has a D.C. conductive path fromsource to load, or where branched channels areinvolved, from or to the common junctionpoint of the channels to the separate loads orfrom the separate sources or between commonjunction points in parallel channels; and at leastone other channel has its signal transmissionpath, as set forth above, involves coupling cir-cuits which will conduct only A.C. signals,because of signal coupling by a series con-denser or transformer, and which will not con-duct D.C. in that signal channel circuit.


ing input-output comparison.10, for modulator-demodulator type

amplifiers.

126 Amplifying different frequencies in differentchannels:This subclass is indented under subclass 124.Subject matter wherein at least one of the chan-nels amplifies a signal of a different frequencyfrom at least one other channel.

SEE OR SEARCH CLASS:381, Electrical Audio Signal Processing

Systems and Devices, subclasses111+, for amplifier systems includingmicrophones and/or loud speakershaving plural amplifier channelswhich pass different frequency bands.

127 WITH CONTROL OF POWER SUPPLYOR BIAS VOLTAGE:This subclass is indented under the class defini-tion. Subject matter combined with means tocontrol the voltage of the source of electricalenergy which is supplied to the amplifyingdevice, or combined with means to control abias voltage applied to an electrode, such con-trol means, generally, being applied to stabilizethe power supply or bias voltage or to alter theoperation of the amplifying device in a prede-termined manner as, for example, to control thesignal amplitude, or means to regulate thepower, heater, or filament supply of the ampli-fying device.

(1) Note. Limiters of the active elementtype which “clip” the signal are not clas-sified herein. Limiters combined withamplifiers where the bias of an electrodeof the amplifier is controlled to “accom-modate” a given maximum signal(where there is no clipping of the signal)are classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:9, for amplifiers with periodic switching

input-output comparison.11, for amplifiers having D.C. reinsertion

circuits.51, for amplifiers combined with auto-

matic disabling switch means.52, for amplifiers having pilot frequency

control means.59, for amplifiers having light control or

activated means.70+, for series energized vacuum tube

amplifiers.85, for signal feedback amplifiers having

an amplifier in the feedback pathincluding the control of bias of suchfeedback amplifiers.

86, for signal feedback amplifiers havinga separately controlled variableimpedance in the feedback path.

96, for signal feedback amplifiers havingbias voltage control of the signalamplifier.

113, for polyphase power supply.114+, for unrectified A.C. power supply for

an electrode.123, for control of bias voltage or power

supply voltage in push-pull amplifi-ers.


144+, for amplifiers having a variableimpedance for the signal path variedby a separate control path.

164, for cascaded amplifiers having anelectronic tube or diode in the inter-stage coupling.

174, for cascaded amplifiers having anelectro-mechanical transducer (e.g.,piezoelectric crystal in the interstagecoupling path.

179, and 180, for cascaded amplifiers hav-ing an inductance in the anode or grid


1April 2009

circuit, or a resistance in the anodeand grid circuit in the capacitance-coupled interstage coupling, respec-tively.

183, for cascaded amplifiers having a non-linear device in the D.C. interstagecoupling path.

199+, for amplifiers with significant poweror bias voltage supply.

254, and 278+, for semiconductor amplifi-ers having signal amplitude (volumelevel) control including such meanswhere the bias is controlled.

290, for semiconductor amplifiers havingD.C. feedback bias control for stabili-zation.

297, for series energized cascaded semi-conductor amplifiers.


nection Systems, subclasses 31+ and52+ for current or voltage control ofelectrical transmission or interconnec-tion systems.

323, Electricity: Power Supply or Regula-tion Systems, for limiters of the activeelement type which “clip” the signal;see appropriate subclasses for voltagemagnitude control systems generally.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 309+ for amplitude limit-ing means.

329, Demodulators, appropriate sub-classes for automatic control of thebias of a demodulating element.

333, Wave Transmission Lines and Net-works, particularly subclasses 2+ forautomatic control of plural channelpassive networks, subclass 14 forcompressors and expanders, sub-classes 15 and 16 for pilot signal con-trolled systems, subclasses 17.1+ forautomatically controlled lines or net-works, and subclass 81 for attenua-tors. See also the search Notes underthese subclasses.

338, Electrical Resistors, for the structureof resistors, rheostats, and potentiom-eters, per se.

455, Telecommunications, subclasses234.1 through 253.2 for automaticvolume control in radio receivers; and

subclasses 343.1-343.6 for particularpower or bias supply for radio receiv-ers.

128 Control means for anode of screen grid cir-cuit:This subclass is indented under subclass 127.Subject matter wherein the “combined controlmeans” is in the circuit from the power supplyor bias voltage source means to the anode orscreen grid electrode of a vacuum tube ampli-fying device or in shunt therewith, in suchmanner, as to control the power supply or biasvoltage applied to the anode or screen gridelectrode.

(1) Note. Ordinary anode or screen gridresistors as such are not control meanssuch as is classified in this subclass.However glow tubes, nonlinear resistors,diodes, vacuum tubes, etc., in the anodeor screen grid supply circuit for voltageregulation and related subject matter areclassified herein. Such matter involvingordinary resistors or other nonlinearimpedances in the power or bias supplycircuits are classified in the appropriatecoupling subclass, when the particularnonlinear element affects the signal cou-pling, and not the power supply. Subjectmatter wherein such impedance is iso-lated from the signal path or is involvedonly in the power supply circuit or formsthe means for isolating the power supplycircuit and is not involved in signal cou-pling as, for example, signal by-passmeans for the power supply, classifica-tion is in the appropriate subclassindented under subclass 199 below.

(2) Note. Nonlinear impedances, vacuumtube impedances, thermal impedances,etc., in amplifier circuits as indicated areclassified in this class. See the searchnotes below.

SEE OR SEARCH THIS CLASS, SUB-CLASS:52, for pilot frequency control means

which may utilize thermal or othernonlinear control means.

70+, for series energized vacuum tubeamplifier devices having the anode


April 2009

energized through the discharge pathof a controlled vacuum tube.

86, for signal feedback amplifiers havinga variable impedance in the feedbackpath.

95, and 110, for nonlinear impedance inthe cathode impedance feedback pathand for a nonlinear impedance ele-ment in the loop path of feedbackamplifiers respectively.

96, for feedback amplifiers combinedwith control of bias voltage of the sig-nal amplifier.

123, for control of anode or screen gridvoltage in push-pull amplifiers.

131, for amplifiers having a bias controlvoltage applied to an electrode sepa-rate and distinct from the signal inputelectrode.

143, for a thermally responsive impedancein the amplifier circuit (when not spe-cifically involved in power or biassupply circuit as in subclass 128).

144+, for variable impedance for the signalchannel, controlled by a separate con-trol path, particularly subclass 145where the variable impedance is anelectron tube or a diode.

164, for amplifier interstage couplingincluding an electronic tube or diode.

174, for amplifiers having an electrome-chanical transducer (e.g., piezoelectriccrystal) in an interstage coupling cir-cuit.

183, for amplifiers having a nonlineardevice in a D.C. interstage coupling.

254, and 278+, for semiconductor amplifi-ers including nonlinear impedanceelements used for signal volume levelcontrol.

256, 272 and 289, for semiconductoramplifiers including transistor tem-perature control.

290, for semiconductor amplifiers havingbias control D.C. feedback stabiliza-tion which may involve nonlinearimpedance elements.

291, for semiconductor signal feedbackamplifiers which may involve nonlin-ear impedance elements.

296, 297, for semiconductor cascadedamplifiers series energized for powerinvolving bias or power supply cir-cuitry.

299+, for semiconductor amplifiers com-bined with a semiconductor imped-ance device.

129 With control of input electrode or gain con-trol electrode bias:This subclass is indented under subclass 127.Subject matter wherein the “means to controlthe bias voltage” is applied to an input elec-trode of the amplifying device, or to an elec-trode separate and distinct from the signal inputelectrodes and in vacuum tube amplifiers alsoseparate and distinct from the anode or screengrid electrodes in order to control the bias ofsuch electrode.


ing input-output comparison.11, for amplifiers with D.C. reinsertion

circuits.52, for amplifiers have pilot frequency

control means.85, for signal feedback amplifiers having

an amplifier in the feedback pathincluding such feedback amplifiershaving means to control the bias of aninput or gain control electrode,thereof.

96, for amplifiers having signal feedbackwith means to control the bias voltageon an electrode of the signal amplifier.

123, for bias voltage control of input orgain control electrode in push-pullamplifiers.

254, and 278+, for semiconductor amplifi-ers having signal volume level con-trol.

290, for semiconductor amplifiers havingD.C. feedback bias control for stabili-zation.


tion Systems, subclasses 227 and 291for discharge control devices for volt-age magnitude control including biascontrol means.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 309+ for miscellaneouscircuits including bias voltage controlmeans for amplitude limiting.


1April 2009

333, Wave Transmission Lines and Net-works, subclasses 14, 15 and 213+ forcompanders, pilot line controlled sys-tems, and active element negativeresistors or reactors, respectivelyincluding such subject matter withbias control means.

363, Electric Power Conversion Systems, appropriate subclasses for electricalconversion, including control of theline voltage.

455, Telecommunications, subclasses234.1 through 253.2 for automaticvolume control in radio receivers; andsubclasses 343.1-343.6 for particularpower or bias supply for radio receiv-ers.

130 Bias controlled by separate external controlsource:This subclass is indented under subclass 129.Subject matter wherein the “means to controlthe bias voltage” includes a source of controlvoltage from a system outside the amplifiersystem itself.

(1) Note. An example is a seismic amplifierwherein a battery not involved in supply-ing amplifier power or bias voltagecharges an RC circuit which is applied tothe control grid or an input grid of theamplifier when the shot blast is fired.Such additional means where it includesthe detector or other related means of theseismic system, per se, is not classifiedherein. See the Search Class notesbelow.

(2) Note. Subject matter, wherein the con-trol voltage is derived from a specialpilot frequency voltage transmitted tothe amplifier with the signal to be ampli-fied, is not classified herein.

(3) Note. Subject matter wherein an oscilla-tor (exclusive of any other source exter-nal to the amplifier) supplies the controlbias is not classified herein. Alsosources of bias voltage as such, where nocooperation from a system outside theamplifier is involved are classified withamplifiers. Where specific details of theexternal system are claimed as in theexample under (1) Note above, as quali-

fied in the last three lines, classificationis not with amplifiers but with the exter-nal system.

SEE OR SEARCH THIS CLASS, SUB-CLASS:51, for amplifiers combined with auto-

matic disabling switch means.52, for subject matter, wherein the control

voltage is derived from a special pilotfrequency voltage transmitted to theamplifier with the signal to be ampli-fied. See (2) Note above.

85, for amplifiers having an amplifier inthe feedback path including bias con-trol means for an electrode of suchamplifier.

86, for amplifiers having a variableimpedance in a feedback control pathvaried by a separate control path.

137, for amplifiers having bias controlmeans including an oscillator in thecontrol means. See (3) Note above.

143, for amplifiers having a thermallyresponsive impedance which may becontrolled from an external controlsource.

144+, for amplifiers having a variableimpedance for the signal channel con-trolled by a separate control pathwhich may be from an externalsource.


linear Devices, Circuits, and Systems, subclasses 309+ for miscellaneouscircuits including bias voltage controlmeans for amplitude limiting.

333, Wave Transmission Lines and Net-works, subclasses 15, 16 and 17.1+for pilot line, pilot current and auto-matically controlled passive wavetransmission systems.

367, Communications, Electrical: Acous-tic Wave Systems and Devices, sub-classes 14+, for means means whereincluding the detector or other relatedmeans of the seismic system, per se.See (1) Note above.

455, Telecommunications, particularlysubclasses 232.1+ and 341+, for simi-lar subject matter in radio receivers.


April 2009

131 Control of bias on separate gain controlelectrode:This subclass is indented under subclass 129.Subject matter wherein the bias control voltageis applied to an electrode of the amplifyingdevice separate and distinct from the electrodesto which the signal input is applied.

(1) Note. Subject matter as above in whichthe separate and distinct electrode towhich the bias voltage is applied is thescreen grid or anode of a vacuum tubeamplifying device is not classifiedherein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:128, for subject matter as above in which

the separate and distinct electrode towhich the bias voltage is applied is thescreen grid or anode of a vacuum tubeamplifying device.

132 Frequency selective means to select controlsignal from amplifier channel:This subclass is indented under subclass 129.Subject matter wherein the “means to controlthe bias voltage” is derived from the electricalsignal channel through a frequency selectivemeans.

SEE OR SEARCH THIS CLASS, SUB-CLASS:52, for pilot frequency control amplifiers

including subject matter wherein thepilot control is derived from the signalchannel by frequency selectivemeans.

85, for amplifiers having an amplifier inthe feedback path including thosehaving bias voltage control whichmay be derived by frequency selectivemeans.

86, for amplifiers having a variableimpedance means in the signal feed-back path controlled by a separatecontrol which may be derived by afrequency selective means from thesignal channel.

109, for signal feedback amplifiers havingfrequency responsive means in thefeedback path.

143, for amplifiers having thermallyresponsive impedance which may becontrolled by a voltage derivedthrough a frequency selective meansfrom the signal channel.

144+, for amplifiers having a variableimpedance for the signal channel con-trolled by a separate control path,wherein the control voltage may bederived from the signal channel by afrequency responsive means.

133 Different bias control means for differentstages of cascade amplifier:This subclass is indented under subclass 129.Subject matter including at least two stages ofamplification (each stage as defined in the classdefinition with at least two such stages asdefined in subclass 129) such that the input sig-nal of each stage except the first is the outputsignal of the preceding stage and wherein thebias control for each of at least two of thestages as defined in subclass 129 has somecharacteristic or characteristics distinctive fromthe other.

134 Plural different bias control voltages pro-vided by separate means:This subclass is indented under subclass 129.Subject matter including at least two separateand distinct bias voltage control means astherein defined, wherein the control voltagesare applied to input or gain control electrodes,and which may be applied to a single amplify-ing device or to more than one amplifyingdevice.

(1) Note. The two separately developed biascontrol means may be combined or com-pared or separately applied in some man-ner as a single bias control means to asingle electrode.

135 Amplitude limiting or bias voltage:This subclass is indented under subclass 129.Subject matter including means to limit themaximum amplitude of the bias control volt-age.

SEE OR SEARCH THIS CLASS, SUB-CLASS:11, for amplifiers having D.C. reinsertion

circuits.


1April 2009

138, for amplifiers with voltage delay forbias control where the bias control isnot effective until a predeterminedminimum voltage is reached wheresuch minimum voltage is fixed bybiasing a rectifier or control dischargedevice so that it will not conduct untilsuch voltage is reached.


linear Devices, Circuits, and Systems, subclasses 309+ for miscellaneouscircuits with amplitude limitingmeans.

329, Demodulators, appropriate sub-classes for automatic control of thebias of a demodulating element.

136 Bias control signal from input of amplifier:This subclass is indented under subclass 129.Subject matter wherein “the bias control volt-age” is derived from the input circuit of theamplifying device.


ing for input-output comparisonincluding those amplifiers wherein abias control voltage for drift correc-tion is developed from such compari-son means.

11, for amplifiers having D.C. reinsertioncircuits.

137 Oscillator supplies or controls bias:This subclass is indented under subclass 129.Subject matter wherein the bias voltage controlmeans includes an oscillator which may beitself controlled by a bias voltage means andfrom which a signal amplifier bias voltage isderived, or from which a control voltage, usu-ally constant, is derived.

SEE OR SEARCH THIS CLASS, SUB-CLASS:52, for amplifiers having pilot frequency

control means.130, for amplifiers including bias voltage

control from a source in a systemexternal to and independent from theamplifier. See (3) Note under sub-class 130 above.

138 Bias controlled by biased rectifier or dis-charge device:This subclass is indented under subclass 129.Subject matter wherein the “bias voltage con-trol means” includes a rectifier or dischargedevice which is biased in such a manner thatthe rectifier or discharge device will not con-duct until a predetermined voltage is reached,which imparts to the control means a “voltagedelay” action and wherein the minimum volt-age at which bias control begins may be prede-termined.

SEE OR SEARCH THIS CLASS, SUB-CLASS:134, for amplifiers having plural different

bias voltages provided by separatemeans including those with biasedrectifiers or discharge devices.


linear Devices, Circuits, and Systems, subclasses 309+ for miscellaneousthreshold limiters of the active ele-ment type.

139 Electronic tube controls bias:This subclass is indented under subclass 129.Subject matter wherein “the bias voltage con-trol means” includes an electronic tube to con-trol the bias voltage which tube may be a gastube or vacuum tube having a means for con-trol thereof while the tube is in operation.


ing input-output comparison includ-ing those with electronic tubes forcontrol.

11, for amplifiers having D.C. reinsertioncircuits.

85, for amplifiers having amplifiers in thefeedback path including bias controlfor the feedback amplifier.

86, for feedback amplifiers having a vari-able impedance in the feedback pathvaried by a separate control means,including those wherein the variableimpedance is an electronic tube.


April 2009

95, and 110, for signal feedback amplifi-ers with nonlinear impedance whichmay be an electronic tube.

96, for signal feedback amplifierswherein the signal amplifier has biasvoltage control means, includingamplifiers with an electron tube insuch bias control means.

114, for amplifiers with oscillators supply-ing or controlling the bias.

123, for push-pull amplifiers having biasvoltage control means including thosewith electronic tubes, in the bias con-trol means.

134, for amplifiers with plural differentbias voltages including electronictube.

138, for amplifiers controlled by biasedrectifiers or discharge devices.

145, for amplifiers having an electronictube or diode as a variable impedancefor the signal channel, controlled by aseparate control path.

164, for amplifiers with an electronic tubeor diode in the interstage coupling.See the search notes thereunder.

296, for semiconductors amplifiers includ-ing those with other transistors forbias control.


tion Systems, appropriate subclasses,for electronic tubes in voltage magni-tude control circuits generally.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 530+ for miscellaneouselectron tube circuits with bias controlmeans.

333, Wave Transmission Lines and Net-works, subclass 14 for amplitudecompression and expansion systems,subclasses 15 and 16 for pilot signalcontrolled systems, 17.1+ for auto-matically controlled systems and213+ for negative resistance or reac-tance active element networks.

140 Rectifier in bias control circuit:This subclass is indented under subclass 129.Subject matter combined with a rectifier in “thebias voltage control means”.


ing input-output comparison.11, for amplifiers having D.C. reinsertion

circuits.52, for pilot frequency controlled amplifi-

ers.85, for amplifiers having amplifiers in the

feedback path including those withbias voltage control having rectifiersin the control means.

86, for amplifiers having variable imped-ance in the feedback path controlledby a separate control path.

95, and 110, for signal feedback amplifi-ers having nonlinear means whichmay be a diode.

96, for signal feedback amplifierswherein the signal amplifier is pro-vided with bias control including suchbias control containing a rectifier.

123, for push-pull amplifiers includingthose having bias control means withrectifiers therein.

134, for amplifiers having plural differentbias voltages provided by separatemeans including those having biasedrectifiers in the control circuit.

138, for amplifiers having bias voltagecontrol means including a biased rec-tifier or discharge device.

145, for amplifiers having an electronictube or diode as a variable impedancefor the signal channel controlled by aseparate control path.

164, for amplifiers having a diode in theinterstage coupling (see search notesunder subclass 164).

254, and 278+, for semiconductor amplifi-ers having signal volume level con-trol.


linear Devices, Circuits, and Systems, subclass 330 for miscellaneous elec-tron tube circuits with amplitude lim-iting and including a rectifier.

363, Electric Power Conversion Systems, appropriate subclasses for rectifiercircuits.


1April 2009

141 Time constant circuit in bias control circuit:This subclass is indented under subclass 129.Subject matter wherein “the bias voltage con-trol means” includes a circuit of resistive andreactive elements, usually of resistive andcapacitive elements, which serves to filter or“smooth out” the D.C. bias voltage applied forcontrol purposes to the amplifier device andwherein specific details or distinctive charac-teristics of such circuit are claimed.

(1) Note. Excluded from this subclass arethe resistive capacitive networks for self-biasing a vacuum tube amplifyingdevice.

SEE OR SEARCH THIS CLASS, SUB-CLASS:142, for resistive capacitive networks for

self-biasing a vacuum tube amplifyingdevice

143, for amplifiers having a thermallyresponsive impedance element includ-ing those with separate controlthereof.

144+, for variable impedance for signalchannel controlled by separate controlpath.

199+, for amplifiers and their power or biasvoltage supply.

254, and 278+, for semiconductor amplifi-ers having signal amplitude (volumelevel) control.

290, for semiconductor amplifiers havingD.C. feedback for bias control.

296, and 297, for semiconductor devicebias or power supply circuitry.

SEE OR SEARCH CLASS:320, Electricity: Battery or Capacitor

Charging or Discharging, subclasses166+ for charging or discharging acapacitor, per se.

333, Wave Transmission Lines and Net-works, subclasses 138+, for passivetime delay networks, subclasses 181+,for smoothing type passive filter net-works.

363, Electric Power Conversion Systems, subclasses 44+ for conversion sys-tems including D.C. smoothing filternetworks.

455, Telecommunications, subclasses234.1 through 253.2 for automaticvolume control in radio receivers; andsubclasses 343.1-343.6 for particularpower or bias supply for radio receiv-ers.

142 Cathode resistor supplies bias (e.g., self-biasing circuits):This subclass is indented under subclass 129.Subject matter involving a vacuum tube ampli-fying device whose input electrode bias voltageand/or bias control voltage for the same ampli-fying device is supplied from a resistive circuitnetwork in the cathode to ground path of thevacuum tube amplifying device whereby theplate current flowing through such resistor,which is usually by-passed for signal currentfrequencies, develops a D.C. bias voltage at thecathode.

(1) Note. The subject matter in this subclassincludes both adjustable self-biasingmeans cathode circuit self-biasingmeans, per se, without an adjustable fea-ture, for vacuum tube amplifying deviceinput electrodes. Input electrode biasmeans without a control feature is classi-fied elsewhere.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for amplifiers having series energized

amplifiers devices.87+, for cathode impedance feedback.203, and 204, for input electrode biasing.

See (1) Note above.254, and 278+, for semiconductor transis-

tor amplifiers having signal amplitude(volume level) control.

290, for semiconductor amplifiers havingD.C. bias control feedback for stabili-zation.

296, and 297, for semiconductor amplifiersinvolving bias or power supply cir-cuitry.


linear Devices, Circuits, and Systems, subclasses 530+ for miscellaneouselectron tube circuits with particularbias means.


April 2009

143 THERMALLY RESPONSIVE IMPED-ANCE:This subclass is indented under the class defini-tion. Subject matter wherein the amplifier con-tains in its circuit an impedance element whoseimpedance value is responsive to the tempera-ture changes therein by reason of the heat gen-erated by the current flow therethrough, or theambient temperature of the impedance ele-ment, or whose impedance value may bechanged by separate electrical control means orother heat control means.

(1) Note. Heat responsive impedance ele-ments are species of nonlinear imped-ance elements and, as such, whenappearing in a cathode impedance feed-back circuit or generally in the loop pathof a feedback amplifier are not in thissubclass. Nonlinear impedances, includ-ing thermal impedances, in a feedbackpath which are varied by separate controlmeans are classified elsewhere. Ther-mally responsive impedance means forma control means and when appearing inthe voltage or power supply circuits of apush-pull amplifier are classified else-where in this class; and when appearingin the power supply or bias supply cir-cuits, as for example, in the circuit fromthe voltage power supply to the anode orscreen grid or in the bias supply circuitso as to control the bias of a vacuum tubeamplifier device, classification is notherein but in the appropriate subclass ofthis class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:86, for nonlinear impedances, including

thermal impedances, in a feedbackpath which are varied by separate con-trol means. See (1) Note above.

95, and 110, for heat responsive imped-ance elements when appearing in acathode impedance feedback circuitor generally in the loop path of a feed-back amplifier . See (1) Note above.

123, for thermally responsive impedancemeans forming a control means andappearing in the voltage or power sup-ply circuits of a push-pull amplifier.

127+, when appearing in the power supplyor bias supply circuits, as for example,in the circuit from the voltage powersupply to the anode or screen grid orin the bias supply circuit so as to con-trol the bias of a vacuum tube ampli-fier device. See (1) Note above.

144+, for variable impedance for the signalchannel controlled by separate controlpath.

157+, appropriate subclasses thereunder foramplifier interstage coupling whichmay include a nonlinear device otherthan one thermally responsive, partic-ularly subclass 164, for electronictube or diode, and subclass 174, forelectromechanical transducer (e.g.,piezo-electric crystal) in the interstagecoupling, and subclass 183, for a non-linear device generally (other thanthermally responsive) in a D.C. inter-stage coupling circuit.

185+, for nonlinear impedance elements,other than thermally responsive,inamplifier input circuits.

192+, for nonlinear impedance elements,other than thermally responsive, inamplifier output circuits.

256, 272 and 289+, for semiconductoramplifiers with transistor temperaturecontrol.

296, and 297, for semiconductor amplifiersinvolving bias or power supply cir-cuitry.


tion Systems, subclass 294 for ther-mally responsive impedance meansfor voltage magnitude control, gener-ally.

336, Inductor Devices, appropriate sub-classes for inductor structure particu-larly subclass 30, for conditionresponsive inductor adjusting means,including those responsive to thermalconditions.

338, Electrical Resistors, subclasses 20+for resistors whose value is responsiveto the current therethrough or the volt-age thereacross and subclasses 25+for resistors whose value varies inresponse to ambient temperature con-ditions.


1April 2009

361, Electricity: Electrical Systems andDevices, subclass 282 for thermallyresponsive condensers, per se.

144 VARIABLE IMPEDANCE FOR SIGNALCHANNEL CONTROLLED BY SEPA-RATE CONTROL PATH:This subclass is indented under the class defini-tion. Subject matter wherein there is providedfor the signal transmission path a variableimpedance element or circuit which may be avariable resistance, or reactance, whose imped-ance is controlled by a separate control means.

(1) Note. Examples of control of variableimpedances classified in this andindented subclasses are; a control volt-age secured from the signal output whichmay be rectified, filtered and applied to abiased diode or to the control electrodeof an electronic tube to vary its imped-ance, or to control an electric motorwhich may vary a potentiometer oradjustable reactance in the signal path.

(2) Note. Considering the signal couplingmeans as a four terminal network the“variable impedance” of the subclassmay be in series between correspondingterminals or in shunt across the signaltransmission path.


control means.70+, for series energized vacuum tube

amplifiers.85, for signal feedback amplifiers having

an amplifier in the feedback path.86, for signal feedback amplifiers having

a variable impedance in the feedbackpath varied by a separate control path.

95, and 110, for signal feedback amplifi-ers having a nonlinear impedance inthe feedback path.

96, for signal feedback amplifiers havingmeans to control the amplifier biasvoltage.

108, for potentiometer common to signaland feedback paths.

127+, for amplifiers having control of powersupply or bias voltage, particularlysubclasses 138, 139, and 140.

143, for thermally responsive impedance inthe signal path including those variedby a voltage or other means from aseparate control path.

155, for amplifiers having unicontrol cou-pling.

164, for cascaded amplifiers having anelectronic tube or diode in an inter-stage coupling circuit.

174, for cascaded amplifiers having anelectromechanical transducer (e.g.,piezo-electric crystal) in an interstagecoupling path.

183, for cascaded amplifiers having a non-linear device in a D.C. interstage cou-pling.

185+, for variable impedance in amplifierinput networks.

192+, for variable impedance in amplifieroutput networks.

293, and 296, for series energized semicon-ductor amplifiers.

299+, for combined diverse type semicon-ductors where one may be a variableimpedance for the signal transmissionpath.


tion Systems, subclasses 234 through289 for transformer and impedancesystems for voltage magnitude con-trol.

324, Electricity: Measuring and Testing, subclasses 98, 99+, and 101 for elec-trical measuring and testing circuitshaving bridges with variable imped-ances thereon, which are varied by aseparate control means.

333, Wave Transmission Lines and Net-works, appropriate subclasses particu-larly subclasses 14, 15, 16, 17.1+, 81,and 213+ for wave transmission sys-tems with variable impedance in thewave transmission path.


336, Inductor Devices, appropriate sub-classes for the structure of variableinductors.

338, Electrical Resistors, appropriate sub-classes for the structure of variableresistance devices.


April 2009

361, Electricity: Electrical Systems andDevices, subclasses 277+ for variablecondenser structure.

145 Electron tube or diode as impedance:This subclass is indented under subclass 144.Subject matter wherein the variable impedancemeans is an electron tube, either vacuum tubeor gaseous which has a control means effectiveduring operation of the tube, or a diode.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for series energized vacuum tube

amplifying devices.85, for signal feedback amplifiers having

an amplifier in the feedback path.138, 139 and 140, for amplifiers having

means to control the input electrodebias voltage including respectively,biased rectifiers or discharge devices,electronic tube, or rectifier in the biascontrol circuit.

164, for cascaded amplifiers having anelectronic tube or diode in the inter-stage coupling circuit.

185+, for amplifier input coupling networkswhich may have an electronic tube ordiode as an impedance therein.

192+, for amplifier output coupling net-works which may have an electronictube or diode impedance therein.

299+, for combined diverse type semicon-ductors where one of the semiconduc-tors may be a diode or transistorimpedance for the signal transmissionpath.


tion Systems, subclasses 227 and 291for discharge devices on voltage mag-nitude control systems generally.

333, Wave Transmission Lines and Net-works, subclasses 213+ for negativeresistance and/or reactance networksof the active element type.

334, Tuners, subclasses 14+ for a tunerunit in which a reactance tube is used.

146 WHEATSTONE BRIDGE WITH AMPLI-FIER IN AT LEAST ONE ARM:This subclass is indented under the class defini-tion. Subject matter wherein the four arms of aWheatstone bridge comprise four impedancesof the amplifier circuit in such manner that atleast one of the four impedances of the bridgeis the discharge path of the amplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:72, for series energized vacuum tube

amplifying devices with at least twoof the devices arranged in the arms ofa bridge.

76+, for amplifiers for compensating forinterelectrode impedance (neutraliza-tion) by feedback where the input-out-put interelectrode impedance couplingand compensating circuits may bearranged in a balanced bridge.

81, for push-pull feedback amplifiersincluding plural stages which mayhave a bridge-like arrangement.

118, for push-pull vacuum tube amplifiersincluding those having plural stageswith a bridge-like arrangement.

175, for interstage coupling circuits includ-ing bridge networks.

273+, for push-pull semiconductor amplifi-ers including those with plural stagespresenting a structure similar to abridge.

293, and 296, for plural stage semiconduc-tor amplifiers series energized whichmay include bridge arrangements.


tion Systems, subclasses 252, 333,and 365 for various impedance bridgearrangements, for voltage magnitudeor phase control; see also the searchnotes under the above subclasses.

333, Wave Transmission Lines and Net-works, subclass 169 for wave filtershaving a Wheatstone bridge arrange-ment. See also the search notes there-under.


1April 2009

147 PLURAL SIGNAL INPUTS:This subclass is indented under the class defini-tion. Subject matter wherein at least two sepa-rate and independent sources of signal energyare coupled to the input of the amplifyingdevice.

(1) Note. Where each of the separatesources has an amplifying device in itsinput circuit before being jointly coupledto an amplifying device, classification isnot herein.

(2) Note. The two separate sources need notoperate to feed signal energy to theamplifying device simultaneously butmay operate selectively, for example, asby switching the sources whereby one isfeeding the amplifying device at a time.

(3) Note. A balanced circuit is treated as asingle source in this class. See the defi-nition and notes under subclass 116above.


parameter type coupling means.69, for sum and difference amplifiers.74, for series energized vacuum tube

amplifiers having plural separateinputs to series devices.

84, for signal amplifiers having pluralamplifier channels.

124+, see (1) Note above, also for pluralseparate inputs to plural channels.

185+, for amplifiers having significant inputnetworks.

252+, for semiconductor amplifiers havingplural inputs or plural channels.


nection Systems, subclasses 18+ and43+ for electrical transmission orinterconnection systems having plu-ral supply circuits or sources.

148 PLURAL SIGNAL OUTPUTS:This subclass is indented under the class defini-tion. Subject matter wherein at least two sepa-rate signal output circuits are coupled from the

output electrode or element of the signal ampli-fying device, for coupling to separate loaddevices.

(1) Note. Where at least two of the signaloutput circuits each contain a signalamplifying device for amplifying thesignal, classification is not herein butwith plural signal amplifier channels.

(2) Note. Any one or more of the separatesignal output circuits may be switchedselectively; operation need not be simul-taneous for classification in this sub-class.

(3) Note. A balanced circuit is treated as asingle load in this class. See definitionand notes for subclass 117 above.


parameter type coupling means.73, for amplifiers having series energized

amplifying devices having plural sep-arate output circuits.

84, for signal feedback amplifiers havingplural amplifier channels.

124+, for plural signal amplifier channel,also for separate outputs from pluralchannels. see (1) Note above.

192+, for amplifiers with significant signaloutput circuit networks.

252+, for semiconductor amplifiers withplural separate signal outputs or pluralchannels.


nection Systems, subclasses 11+ forelectric transmission or interconnec-tion systems having plural load circuitsystems.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous circuits having plural outputs.

329, Demodulators, subclasses 316+ forplural outputs in frequency demodula-tor and subclass 348 for plural outputsin an amplitude demodulator.


April 2009

333, Wave Transmission Lines and Net-works, subclasses 100+ for wavetransmission lines and networks hav-ing branched circuits.

149 HUM OR NOISE OR DISTORTIONBUCKING INTRODUCED INTO SIGNALCHANNEL:This subclass is indented under the class defini-tion. Subject matter wherein the signal has ahum or noise component inadvertently intro-duced therein, as where there is ineffective fil-tering of a rectified A.C. power supply or bias,and wherein such objectional component isremoved or reduced by the same hum or noisecomponent introduced into the signal path ofthe amplifier in such manner as to oppose theobjectional signal component, thereby remov-ing it from, or reducing it in, the output signal.

(1) Note. Where such component isremoved or reduced by negative feed-back classification is elsewhere.

SEE OR SEARCH THIS CLASS, SUB-CLASS:75+, where such components of this sub-

class (149) are removed or reduced bynegative feedback. See (1) Noteabove.

114, for amplifiers having unrectified A.C.power supply including those withmeans to eliminate hum.

118+, for push-pull amplifiers which includemeans for opposing noise, hum, orother unwanted components inadvert-ently present with the signal, andwherein the compensation is inherentin the push-pull arrangement, per se.

124+, for plural channel amplifiers includ-ing those wherein an unwanted com-ponent in the signal is separatelyamplified and opposes the unwantedcomponent in a channel whichincludes the signal and the unwantedcomponent.

150, for cascaded amplifying devices ofdifferent characteristics includingthose wherein the characteristics ofone stage compensate for those ofanother.

151, for cascaded amplifying devices withmeans to by-pass a stage wherein afeed forward component may oppose

the same component in the signalpath.

199+, for amplifiers with power or bias volt-age supply including filters to elimi-nate hum, etc.

296, and 297, for semiconductor amplifierswith bias or power supply circuitry.


Devices: Systems, subclasses 94+ fordischarge device load systems havingcathode or cathode heater power sup-ply, with or without anode power sup-ply, but excluding control electrodesupply, including those having meansfor hum elimination, etc.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclass 549 for miscellaneous cir-cuits with power supply and hum pre-vention or elimination means.

333, Wave Transmission Lines and Net-works, subclasses 167+ for wave fil-ters, per se, which may be used toeliminate a frequency component,particularly subclasses 181+, forsmoothing filters for power supply.

363, Electric Power Conversion Systems, subclasses 39+ for electrical conver-sion systems including means to elim-inate frequency components.

150 CASCADED SIMILAR AMPLIFYINGDEVICE OF DIFFERENT CHARACTER-ISTICS:This subclass is indented under the class defini-tion. Subject matter including at least twostages of amplification (each stage as definedin the class definition and each stage having avacuum tube amplifying device) such that, theinput signal for each stage, except the first, isthe output signal of the preceding stage, andwherein at least one of the cascaded amplifyingdevices has a significant difference in its char-acteristics such as a difference in the number ofelectrodes, or where the construction of each ofat least two of the tubes is such that there is adifference in the tube characteristics, or wherebecause of differences in biasing or energizingvoltages the tube characteristics are different.

(1) Note. Different types of vacuum tubesrepresenting a genus or class and pro-


1April 2009

vided for above such as traveling wavetubes and magnetrons or traveling wavetubes and secondary emission tubeswhen claimed in cascade are classifiedelsewhere (see the search this class, sub-class notes below) Where vacuum tubes,are different in structural characteristicsor some other feature, but all of the plu-ral tubes fall within one of the genustypes provided for above, as for exampletraveling wave tubes classification iswith the genus type and not in this sub-class.

(2) Note. Beam power tubes, broadlyclaimed with no other distinctive charac-teristics, when combined in cascade withanother vacuum tube such as an ordinarytriode are classified in this subclass andnot in subclass 3 or subclasses 44+above.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for different types of vacuum tubes

representing a genus or class and pro-vided for above such as travelingwave tubes and magnetrons or travel-ing wave tubes and secondary emis-sion tubes when claimed in cascade.Where vacuum tubes, are different instructural characteristics or someother feature, but all of the pluraltubes fall within one of the genustypes provided for above, as forexample traveling wave tubes classifi-cation is with the genus type and notin this subclass (150) nor in subclass3.

6, for magnetrons.42, for traveling wave tubes and second-

ary emission tubes.43, for traveling wave tubes.70+, for series arranged vacuum tube

amplifiers including cascaded ampli-fiers so arranged.

310+, for cascaded semiconductor amplifi-ers, particularly subclass 311 for cas-caded semiconductors of differentcharacteristics.

151 WITH AMPLIFIER BYPASS MEANS(E.G., FORWARD FEED):This subclass is indented under the class defini-tion. Subject matter wherein means are pro-vided to by-pass all or a part of the signalacross the amplifier or of one or more stages ofa cascade amplifier.

(1) Note. For classification herein the by-pass means must be free of any amplify-ing device. Subject matter having suchadditional amplifying device is not inthis subclass.

(2) Note. This subclass includes subjectmatter involving a cascaded amplifier,for switching an amplifier device in orout of the cascaded arrangement.


parameter coupling means, particu-larly subclass 54 for distributedamplifiers.

70+, for series energized amplifiers includ-ing cascaded amplifiers having sucharrangement.

84, for signal feedback amplifiers havingplural amplifier channels.

88+, 92, and 98+, for cascaded amplifiershaving signal feedback.

120+, for cascaded push-pull amplifiers.124+, for by-pass means having additional

amplifying device. See (1) Noteabove.

133, for cascaded amplifiers having differ-ent bias control for different stages.

145, for amplifiers having a separatelycontrolled tube in the signal path.

147, and 148, for amplifiers having pluralsignal inputs and plural signal out-puts, respectively.

157, for amplifier interstage couplings, perse, particularly subclass 164, for anelectronic tube or diode in the cou-pling circuit.

310+, for cascaded semiconductor amplifi-ers.


April 2009


works, subclasses 100+ for wavetransmission passive networkbranched circuits.

152 CASCADED DIFFERENTLY COUPLEDBETWEEN STAGES:This subclass is indented under the class defini-tion. Subject matter including at least threestages of amplification (each stage as definedin the class definition) such that, the input sig-nal for each stage, except the first, is the outputsignal of the preceding stage; and where two ofthe interstage coupling means between succes-sive amplifying devices have different charac-teristics.

(1) Note. The following are examples ofsubject matter classified in this andindented subclasses: one device is cou-pled from the plate and the other fromthe cathode; or one coupling has a tunedcircuit and the other has not; or both cou-plings have circuits tuned to differentfrequencies or the two couplings may besimilar but contain an impedance ele-ment or elements of one having differentvalues from the corresponding element,or elements in the other interstage cou-pling.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for plural diverse type amplifying

devices.53+, for amplifiers having distributed

parameter type coupling.70+, for series energized vacuum tube

amplifiers.88, 92 and 98, for cascaded amplifiers

including signal feedback.120+, for interstage coupling between push-

pull stages of an amplifier.133, for different bias control on different

stages of a cascaded amplifier.150, for cascaded amplifiers with similar

amplifying devices having differentcharacteristics.

151, for amplifiers with means to by-pass astage.

157+, for interstage coupling in an amplifier.

310+, for plural stage cascaded semiconduc-tor amplifiers.


tion Systems, appropriate subclassesfor voltage magnitude and phase con-trol systems generally, with varioustransformer and impedance networksto perform such functions.

333, Wave Transmission Lines and Net-works, subclasses 24+ for couplingnetworks for wave transmission, gen-erally.

153 Including a cathode follower stage:This subclass is indented under subclass 152.Subject matter wherein at least one of the inter-stage coupling means has a cathode followersignal output.

(1) Note. If only the coupling of the laststage is a cathode follower and none ofthe previous stages has a cathode fol-lower output, classification is not in thissubclass. For classification of cathodefollower amplifiers and analogous sub-ject matter see search notes immediatelyfollowing.

SEE OR SEARCH THIS CLASS, SUB-CLASS:119, for push-pull vacuum tube amplifiers

including cathode followers.168, and 172+, for amplifiers having a

cathode follower in the interstage cou-pling.

193+, for amplifiers with cathode followeroutput coupling.

310+, for cascaded semiconductor amplifi-ers which may have an emitter fol-lower stage analogous to cathodefollower in a cascaded vacuum tubeamplifier.

154 Transformer or resonant circuit in inter-stage coupling (e.g., stagger tuning) :This subclass is indented under subclass 152.Subject matter wherein at least one of the inter-stage coupling means has a signal couplingtransformer or a resonant circuit containedtherein.


1April 2009

(1) Note. Stagger tuned amplifiers are clas-sified in this subclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:56, for amplifiers having wave guide,

cavity, or concentric resonator cou-pling means.

120, for interstage coupling between push-pull amplifier stages including trans-former coupling and resonant meansin the coupling circuit.

165+, for amplifiers having transformerinterstage coupling.

302+, for cascaded semiconductor amplifi-ers having frequency responsive sig-nal coupling means.


works, subclasses 24+ for wave trans-mission coupling means, generally,including resonant circuits and trans-former coupling.

334, Tuners, appropriate subclasses fortuners, per se, and especially sub-classes 59+ and 61+ for transformersused in a resonant circuit.

155 UNICONTROL OF COUPLING OR THECIRCUITS ASSOCIATED THEREWITH:This subclass is indented under the class defini-tion. Subject matter wherein two or more ele-ments such as resistors, reactors, etc.., of anycoupling network or different coupling net-works, for transmission of the signal in theamplifier are constructed and arranged so thatadjustment or control is simultaneous for suchtwo or more elements, such adjustment may befor a tuner, a potentiometer, or any other meansor any combination of such means, in the cou-pling circuits or associated circuits.

SEE OR SEARCH THIS CLASS, SUB-CLASS:53+, particularly subclass 56 for distributed

parameter coupling means includingadjustment of such means.

65+, for structure of circuit elements whenin an amplifier which may include thestructure of adjustable circuit ele-ments.

108, for a potentiometer common to thesignal and feedback paths of an ampli-fier.

116, and 117, for amplifiers with balanced-to-unbalanced and unbalanced-to-bal-anced coupling, respectively, whichmay involve adjustable circuit ele-ments.

120, and 122, for coupling of a push-pullamplifier which may involve adjust-able circuit elements in the coupling.

143, for amplifiers with a thermallyresponsive impedance.

144+, for amplifiers having a variableimpedance for the signal channel con-trolled by a separate control path.

157+, for amplifiers with interstage couplingwhich may have an adjustable ele-ment in the coupling.

171, 190 and 197, for transformer struc-ture.

185+, for amplifiers which may have anadjustable element in the input cou-pling.

192+, for amplifiers which may have anadjustable element in the output cou-pling.


works, subclasses 24+, 81 and 219+for coupling means, attenuators, ordistributed parameter type resonators,respectively, including those withvariable circuit elements.


336, Inductor Devices, appropriate sub-classes for variable inductor devices.

338, Electrical Resistors, appropriate sub-classes for the structure of rheostats,and resistors.

361, Electricity: Electrical Systems andDevices, subclasses 277+ for variablecondensers.

156 BOOTSTRAP COUPLING:This subclass is indented under the class defini-tion. Subject matter wherein the signal input isfloating and is applied between the control gridand cathode of a vacuum tube amplifyingdevice, with the cathode having an impedancebetween it and ground which maintains thecathode voltage above ground, by reason of the


April 2009

anode current flowing through such imped-ance.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for series energized amplifiers includ-

ing those having signal couplingbetween cathode and grid similar tothe subject matter in this subclass.

87+, for amplifiers having cathode imped-ance feedback particularly subclass 89for cathode coupling between adja-cent stages.

119, for push-pull amplifiers includingcoupling to the cathode.

153+, for amplifiers having interstage cou-pling to a cathode.

186+, for amplifiers having input couplingto a cathode.


linear Devices, Circuits, and Systems, subclass 589 for miscellaneous elec-tron tube circuits with bootstrap cir-cuit means.

157 INTERSTAGE COUPLING:This subclass is indented under the class defini-tion. Subject matter wherein the amplifier iscomprised of at least two amplifying devices incascade, the two being in direct proximity inthe cascaded circuit and wherein there are sig-nificant details or distinctive characteristics ofthe circuit by means of which the signal outputof the preceding amplifying device is coupledto the signal input of the following cascadedamplifying device, or wherein the parametersor electrical characteristics of the output of thepreceding device or the input of the followingdevice, are claimed.

(1) Note. Subject matter disclosing inter-stage coupling but wherein only the out-put coupling of the first amplifyingdevice is claimed or wherein only theinput coupling of the following amplify-ing device is claimed is classified in thisand appropriate indented subclasses andnot with input or output coupling undersubclasses 185+ or 192+, respectively.

(2) Note. The output of the precedingamplifying device of the cascaded

devices has an output electrode and acommon electrode for the signal and theinput of the following stage has an inputelectrode and a common electrode, toreceive the signal. Thus, there isinvolved a four terminal coupling net-work between output (including com-mon electrode) and input (includingcommon electrode) with usually two-series circuits between output and inputelectrodes and between common elec-trodes respectively and also shunt circuitelements often between such series cir-cuits.


devices which may involve interstagecoupling between such devices.

53+, for coupling of distributed parametertype which may be interstage.

65+, for structure of circuit elements, otherthan transformer structure, which maybe involved in interstage coupling.

70+, for interstage coupling between cas-caded series energized tubes.

88+, 92, and 98+, for interstage coupling incascaded feedback amplifiers.

120, for interstage coupling in push-pullamplifiers.

133, for cascaded amplifiers having biasvoltage control which may involveinterstage coupling.

143, for thermally responsive impedancewhich may be involved in interstagecoupling.

144+, for variable impedance controlled byseparate control path which may beinvolved in interstage coupling.

150, for cascaded stages having amplifiersof different characteristics with inter-stage coupling means.

151, for cascaded stages with means to by-pass a stage.

152+, for diverse types interstage couplingin amplifiers having plural cascadedstages.

155, for unicontrol of coupling meanswhich may involve interstage cou-pling.

156, for bootstrap coupling.185+, for amplifiers with input coupling net-

works. See (1) Note above.


1April 2009

192+, for amplifiers with output couplingnetworks. See (1) Note above.

310+, for plural stage cascaded semiconduc-tor amplifiers, involving interstagecoupling.


works, subclasses 24+, for passivecoupling networks for wave transmis-sion, generally.

158 Coupling to cathode:This subclass is indented under subclass 157.Subject matter wherein the signal derived fromthe preceding cascaded amplifying device iscoupled to the cathode electrode of a followingcascaded vacuum tube amplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:88+, and 91+, for amplifiers applying sig-

nal feedback to the cathode.89, for amplifiers having adjacent cas-

caded stages with cathode-cathodecoupling. See (1) Note thereunder.

119, for push-pull amplifiers with couplingto the cathode.

156, for bootstrap coupling where inputsignal is applied directly between gridand cathode.

186+, for input coupling to the cathode.

159 D.C. coupling:This subclass is indented under subclass 158.Subject matter wherein the interstage couplinghas a D.C. conductive path for signal currentfrom the output electrode of the preceding cas-caded amplifying device to the input electrodeof the following device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:187, for amplifiers with D.C. input cou-

pling to the cathode.

160 Coupling to plate or auxiliary grid:This subclass is indented under subclass 157.Subject matter wherein the signal derived fromthe first of the two cascaded amplifyingdevices is coupled to the screen grid or an elec-trode other than the control grid or cathode,such as the anode electrode or the suppressorgrid of the following cascaded amplifying

device, which device is of the vacuum tubetype.

SEE OR SEARCH THIS CLASS, SUB-CLASS:64, for space charge grid tube amplifiers

wherein the first grid next to the cath-ode is biased positively with respectthereto and the signal input is appliedto the grid next in succession from thecathode which is biased negativelywith respect to the cathode.

185, and 188+, for input coupling to a vac-uum tube amplifying device includinginput coupling to an electrode otherthan the control grid or cathode.


subclass 124 for amplifiers combinedwith an electrical measuring devicewherein the input is applied to theanode of the amplifying device (e.g.,inverted amplifier).

161 D.C. coupling:This subclass is indented under subclass 160.Subject matter wherein the coupling has a D.C.conductive path for signal current from the out-put electrode of the preceding amplifyingdevice to the input, electrode of the followingof the two cascaded vacuum tube amplifyingdevices.

SEE OR SEARCH THIS CLASS, SUB-CLASS:191, for a D.C. amplifier input coupling

which may be to an electrode of a vac-uum tube amplifying device otherthan the control grid or cathode.

162 Output coupling from grid:This subclass is indented under subclass 157.Subject matter wherein the coupling betweenthe two cascaded amplifying devices is from agrid, such as the screen grid, suppressor grid orcontrol grid, or from between such a grid andan anode of the preceding amplifier device (ofthe vacuum tube type) of the two cascadeddevices.


April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:42, for amplifiers having secondary emis-

sion amplifier devices wherein theoutput may be from a secondary emis-sive electrode.

192, and 195, for output coupling from agrid, such as the screen grid, suppres-sor grid or control grid or betweensuch a grid and the anode.


subclass 124 for inverter amplifierscombined with measuring meanswhere the output is from the controlgrid.

163 D.C. coupling:This subclass is indented under subclass 162.Subject matter wherein the coupling has a D.C.conductive signal path from the grid or frombetween the grid and anode of the preceding ofthe two cascaded amplifying devices (of thevacuum tube type) to the following device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:198, for D.C. output coupling which may

involve coupling from a grid or frombetween a grid and the anode.

164 With electronic tube or diode in couplingcircuit:This subclass is indented under subclass 157.Subject matter in which the coupling circuitbetween the two cascaded stages has at leastone path which includes an electronic dis-charge tube (which may be a gas tube or vac-uum tube having control means effectiveduring operation of the tube) or which includesa diode element which may be a glow tube, arectifier vacuum tube diode or a dry rectifierdiode, etc.

(1) Note. The electronic tube or diode per-forms some function, such as an imped-ance, other than serving as an additionalamplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:138, for control of bias or power supply

voltage by a biased rectifier or dis-charge device.

139, and 140, for an amplifier including anelectronic tube or rectifier, respec-tively, to control the input or gain con-trol electrode bias.

143, where the diode or electronic tube is athermally responsive element.

145, where the diode or electronic tube is avariable impedance controlled by aseparate control path.

185+, for amplifier input circuits includingany with an electronic tube or diode,in the input circuit (other than as apreceding amplifying stage).

192+, for amplifier output networks whichmay include an electronic tube ordiode (other than as an amplifyingstage).


works, subclasses 213+ for negativeresistance and/or reactance networkswhich have an active element includ-ing electron tubes or diodes, as suchactive elements.

165 Transformer coupling:This subclass is indented under subclass 157.Subject matter wherein the the signal couplingbetween the two cascaded amplifying devicestages is by means of at least one transformer.

SEE OR SEARCH THIS CLASS, SUB-CLASS:120, for interstage coupling in push-pull

amplifiers including transformer cou-pling.

122, for input or output coupling in push-pull amplifiers including transformercoupling.

154, for transformer coupling in pluralstage cascaded vacuum tube amplifi-ers with at least two interstage cou-pling networks which have somedifferent characteristic.

188+, for transformer coupled amplifierinput circuits.


1April 2009

195+, for transformer coupled amplifier out-put circuits.


works, subclasses 177+ for wavetransmission transformer coupled cir-cuits of the passive type, generally.

334, Tuners, subclasses 59+ and 61+ fortuners having a transformer in the res-onant circuit.

336, Inductor Devices, appropriate sub-classes, for transformer structure.

166 With additional reactive coupling:This subclass is indented under subclass 165.Subject matter wherein, between the primaryand secondary of the transformer, there is anadditional capacitive or inductive reactor ele-ment which carries part of the signal currentcoupled between the two devices.

167 With additional impedance connected to"P" or "S" circuits:This subclass is indented under subclass 165.Subject matter wherein additional impedancewhich may be inductive, capacitive or resistiveis included in either the primary or secondarywinding circuit of the transformer which cou-ples the signal between the two cascadedamplifier devices.

SEE OR SEARCH THIS CLASS, SUB-CLASS:189, for transformer input coupling with

additional impedance connected to theprimary or secondary winding circuit.

196, for transformer output coupling withadditional impedance connected to theprimary or secondary winding circuit.

168 From cathode:This subclass is indented under subclass 165.Subject matter wherein means are provided toderive the signal from the cathode of the pre-ceding amplifying device (of the vacuum tubetype).

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for series energized tubes which may

have a cathode follower output.88+, and 91, for cascaded amplifiers hav-

ing signal feedback to the cathode.

117, for amplifiers having unbalanced-to-balanced coupling including phasesplitters with cathode coupled output.

119, for push-pull amplifier involving cou-pling from the cathode.

153, for different interstage coupling incascaded amplifiers including a cath-ode follower stage.

156, for bootstrap coupled amplifiers.172+, for interstage coupling from the cath-

ode for other than transformer cou-pling.

193, for output networks from the cathodeof the amplifying device.

250+, for semiconductor amplifiers havingemitter signal output analogous tocathode follower output.

169 With means for adjusting inductive cou-pling:This subclass is indented under subclass 165.Subject matter wherein means are provided foradjusting the inductance of either the primaryor secondary winding or the mutual inductancebetween the primary and secondary winding, inthe latter case, for example, by varying theposition of the primary or secondary windingsor parts thereof relative to each other.

SEE OR SEARCH CLASS:334, Tuners, subclasses 61+ for tuners hav-

ing mutual inductance variablemeans.

336, Inductor Devices, appropriate sub-classes particularly subclasses 115+for adjustable coupling by relativelymoving coils, and subclasses 130+ forrelatively movable coil and core tovary the inductance. Class 336 is thegeneral class for the structure ofinductors including means to vary theinductance and mutual inductance.

170 With shielding:This subclass is indented under subclass 165.Subject matter combined with shielding means,for the transformer, or parts thereof.

(1) Note. Under interstage coupling, shield-ing and the structure of shielding areclassified separately (subclass 170) fromother structure of transformers (subclass171). Under input and output couplingno separate provision is made for shield-


April 2009

ing so that all structure of transformersin input or output amplifier couplingincluding shielding is classified in sub-classes 190 and 197, below respectively.

SEE OR SEARCH THIS CLASS, SUB-CLASS:68, for shielding combined with amplifi-

ers or with circuit elements of amplifi-ers, generally.

190, for amplifier input coupling includingtransformer structure which mayinclude shielding.

197, for amplifier output coupling includ-ing transformer structure which mayinclude shielding.


tors, subclasses 350 through 397 ,shielded or screened, for shieldingelectrical elements, generally. See thesearch notes thereunder.

336, Inductor Devices, subclasses 84+ forshielding of inductors, generally. Seethe search notes thereunder.

171 With transformer structure:This subclass is indented under subclass 165.Subject matter involving the structure of thetransformer coupling the signal between thetwo cascaded stages.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65+, for structure of amplifier circuit ele-

ments other than transformersinvolved with an amplifier system.

190, for the structure of transformers inamplifier input coupling.

197, for the structure of transformers inamplifier output coupling.

SEE OR SEARCH CLASS:336, Inductor Devices, appropriate sub-

classes for transformer structure gen-erally.

172 Coupling from cathode:This subclass is indented under subclass 157.Subject matter wherein the signal output iscoupled form the cathode electrode of the pre-ceding vacuum tube amplifier device of the

two cascaded amplifying devices, to the inputof the following amplifier device.


amplifiers which may have an outputcircuit from the cathode.

88, and 91, for cascaded vacuum tubeamplifying devices with signal feed-back from the cathode.

89, for amplifiers having adjacent cas-caded stages with cathode-cathodecoupling.

117, for amplifiers with unbalanced-to-bal-anced coupling including phase split-ters with cathode output coupling.

119, for push-pull amplifiers with couplingfrom the cathode.

153, for plural stage cascaded vacuum tubeamplifying devices with different cou-pling between stages including a cath-ode follower stage.

156, for bootstrap coupling.168, for interstage transformer coupling

from the cathode.193+, for amplifier output coupling net-

works from the cathode of the ampli-fying device (cathode followers) seethe notes and search notes thereunder.

250+, for semiconductor amplifiers havingemitter output analogous to cathodefollower output.

173 D.C. coupling:This subclass is indented under subclass 172.Subject matter wherein the coupling betweenthe two cascaded amplifying devices is a D.C.conductive path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:194, for vacuum tube amplifier device out-

put coupling circuits with D.C. cou-pling from the cathode.

174 With electromechanical transducer (e.g.,piezoelectric crystal):This subclass is indented under subclass 157.Subject matter wherein the coupling circuitbetween the two cascaded amplifier devicesincludes means to convert the electric signal tomechanical vibrations and means further toconvert the mechanical vibrations back to elec-


1April 2009

tric signals, such means, generally, serving aseither time or phase delay means or means todetermine the transmission frequency of thecoupling network.

(1) Note. The electromechanical transducermeans in this subclass is distinguishedfrom subject matter of subclass 60above, wherein the amplifying deviceitself includes a magnetostrictive meanselectromechanical transducer. In thissubclass, the electrical signal energy isnot used to control another source ofelectrical energy applied to the trans-ducer, but herein the electric signal, inbeing transmitted, is converted tomechanical energy and back to electricalenergy.

SEE OR SEARCH THIS CLASS, SUB-CLASS:60, for amplifiers having magnetostrictive

means.185+, for amplifier input circuits including

any having an electromechanicaltransducer. See (1) Note under sub-class 157.

192, for amplifier output circuits includingany having an electromechanicaltransducer. See (1) Note under sub-class 157.


works, subclasses 148+, 186, and187+ for delay lines using electrome-chanical transducers, and for wave fil-ters using electromechanicaltransducers and piezo-electric types ofsuch transducers, respectively. Seethe search notes under these sub-classes.

175 With lattice or Wheatstone bridge networkin coupling circuits:This subclass is indented under subclass 157.Subject matter wherein the coupling includes anetwork having four impedance branches con-nected in series to form a closed circuit, twononadjacent junction points serving as inputterminals while the remaining two junctionpoints serve as output terminals.

SEE OR SEARCH THIS CLASS, SUB-CLASS:72, for plural amplifier devices having

space discharge paths in differentarms of a bridge.

146, for Wheatstone bridge with amplifierin at least one arm.

185+, for amplifier input coupling includingany with a lattice or Wheatstonebridge network. See (1) Note undersubclass 157, above.

192+, for amplifier output coupling includ-ing any with a lattice or Wheatstonebridge network. See (1) Note undersubclass 157, above.


works, subclass 74, sections (1) and(2) of the definition.

176 With T, H, or Pi network in coupling circuit:This subclass is indented under subclass 157.Subject matter wherein the coupling includes aT, H, or Pi circuit network.

SEE OR SEARCH THIS CLASS, SUB-CLASS:185+, for amplifier input circuit networks

including any with a T, H, or Pi circuitnetwork. See (1) Note under subclass157, above.

192+, for amplifier output circuit networksincluding any with a T, H, or Pi circuitnetwork. See (1) Note under subclass157, above.


works, subclasses 24+, appropriatesubclasses thereunder for couplingcircuits which may include T, H, of Pinetworks. See the notes and searchnotes under Class 333, subclass 24.

177 With coupling or blocking capacitor:This subclass is indented under subclass 157.Subject matter wherein any path traced inseries from the output electrode of the preced-ing of the two cascaded amplifying devices tothe input electrode of the amplifier device ofthe following stage contains at least one capac-itor.


April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:120, for push-pull amplifiers with signifi-

cant interstage coupling which mayinclude a blocking capacitor in suchcoupling.

166, for amplifiers with interstage trans-former coupling having additionalreactive coupling which may be acapacitor.

185, and 186, for amplifier capacitor inputcoupling, generally, and to a cathode,respectively.

192, and 193, for amplifier capacitor out-put coupling, generally, and from acathode, respectively.


works, subclasses 24+ for couplingcircuits generally, see notes andsearch notes under subclass 24.

178 With R or L in series between stages:This subclass is indented under subclass 177.Subject matter wherein the series path betweenthe output electrode of the preceding of the twocascaded devices and the input electrode of thesucceeding device has a resistor of inductancein such path in series with the coupling orblocking capacitor.

179 L in anode or grid circuit:This subclass is indented under subclass 177.Subject matter having in addition an inductorconnected to the anode output electrode of thepreceding stage device or to the grid input elec-trode of the following stage device, in shuntacross the signal transmission path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, appropriate subclasses for circuits in

the anode power supply or grid biassupply which may include an induc-tor. See the search notes under sub-class 199, below.

180 With R in anode and grid circuit (RC cou-pling):This subclass is indented under subclass 177.Subject matter having in addition a resistancedirectly connected to the anode output elec-

trode from the anode power supply of the pre-ceding amplifier stage device and a resistancedirectly connected to the input grid electrode ofthe following amplifier stage device from thenegative bias source or ground, each resistancebeing in shunt across the signal transmissionpath.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for power or voltage supply circuits to

the anode or grid electrodes whichmay have resistors therein. See thesearch notes under subclass 199,below.

181 D.C. coupled:This subclass is indented under subclass 157.Subject matter wherein the series couplingfrom the output electrode of the precedingamplifier device to the input electrode of thefollowing amplifier device of the two cascadedstages has a D.C. conductive path.

SEE OR SEARCH THIS CLASS, SUB-CLASS:9, for periodic switching for input-out-

put comparison including drift cor-rected D.C. amplifiers.

10, for modulator-demodulator amplifi-ers for amplifying D.C. signals.

53+, for amplifiers having distributedparameter coupling which mayinclude D.C. interstage coupling.

70+, for series energized amplifiers.121, for push-pull amplifiers having D.C.

interstage coupling.125, for plural amplifier channels involv-

ing a D.C. and an A.C. channel.159, for interstage D.C. coupling to the

cathode.161, for D.C. interstage coupling to the

screen grid or electrode other thancontrol grid or cathode.

163, for D.C. interstage output couplingfrom a grid or between a grid and theanode.

173, for D.C. interstage coupling from thecathode.

187, for input D.C. coupling to the cath-ode.

191, for D.C. input coupling, generally.194, for D.C. output coupling from the

cathode.


1April 2009

198, for D.C. output coupling, generally.289, for D.C. conductively coupled cas-

caded semiconductor amplifiers.293, and 296, for series energized cascaded

semiconductor amplifiers.


works, subclasses 24+ for wave trans-mission coupling, generally. See,also, search notes under subclass 24.

182 With series reactive element between stages:This subclass is indented under subclass 181.Subject matter wherein the series couplingD.C. conductive path between the output elec-trode of the preceding amplifying device andthe input electrode of the following amplifyingdevice contains therein a reactive element,such as an inductor or parallel to a D.C. con-ductive element in the series path there is acapacitive reactive element.

SEE OR SEARCH THIS CLASS, SUB-CLASS:53+, for amplifiers with distributed param-

eter coupling which may involve aD.C. conductive path including areactive element.

107, for signal feedback amplifiers havinga phase shift network in the loop path.

121, for push-pull amplifiers having D.C.interstage coupling including any withseries reactor element.


144+, for amplifiers having a variableimpedance in the signal path con-trolled by a separate control path.

166, for transformer coupled amplifierstages including a D.C. reactive ele-ment (inductor coil) jointing the pri-mary and secondary windings.

175, for amplifiers having a lattice orWheatstone bridge network in theinterstage coupling circuit.

176, for amplifiers having a T, H, or Pi net-work in the interstage coupling.

302+, for semiconductor amplifiers havingfrequency responsive means in thesignal transmission path.

183 With nonlinear device:This subclass is indented under subclass 181.Subject matter wherein the coupling contains adevice whose impedance (which may be resis-tive, capacitive, or inductive or any combina-tion of these) is such that the relationship ofvoltage across the device to the current flowtherein is nonlinear.

(1) Note. The device may be in shunt acrossthe signal transmission path, or in theD.C. series path between the vacuumtube amplifying devices, or in any otherposition in the signal coupling circuit.

SEE OR SEARCH THIS CLASS, SUB-CLASS:86, for signal amplifiers with a variable

impedance in the feedback path whichis varied by a separate control path.

95, for feedback amplifiers having a non-linear impedance means in the cath-ode circuit.

110, for feedback amplifiers having a non-linear impedance element in the looppath.

127+, for nonlinear impedances involved incircuits for the control of amplifierpower supply or bias voltage.


144+, for amplifiers having a variableimpedance for the signal channelwhich is varied by a separate controlpath.

164, for cascaded amplifiers having anelectronic tube or diode in an inter-stage coupling circuit.

174, for cascaded amplifiers having anelectromechanical transducer such asa piezo-electric crystal in an interstagecoupling circuit.

185, or appropriate indented subclass for anonlinear device involved in the inputcoupling.

192, or appropriate indented subclass for anonlinear device involved in the out-put coupling.

299+, for semiconductor amplifiers having adiverse type semiconductor, whichmay be a nonlinear coupling imped-ance.


April 2009

SEE OR SEARCH CLASS:257, Active Solid-State Devices (e.g.,

Transistors, Solid-State Diodes),appropriate subclasses for activesolid-state devices, per se, includingsubclasses 115, 123 and 162 through166 which are directed to devicesinvolving amplification.

307, Electrical Transmission or Intercon-nection Systems, subclasses 401+ fornonlinear reactor systems.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous nonlinear transistor and elec-tron tube circuits.

333, Wave Transmission Lines and Net-works, appropriate subclasses forwave transmission networks whichmay involve nonlinear impedance ele-ments.

338, Electrical Resistors, subclasses 13+for nonlinear resistor elements.

361, Electricity: Electrical Systems andDevices, subclasses 271+ for struc-ture of a capacitor which may be non-linear.

184 With series resistance between stages:This subclass is indented under subclass 181.Subject matter wherein the series couplingD.C. conductive path between the output elec-trode of the preceding amplifying device andthe input electrode of the following amplifyingdevice of the two cascaded amplifying devicescontains therein a resistor.

185 INPUT NETWORKS:This subclass is indented under the class defini-tion. Subject matter involving significantdetail or distinctive characteristics of the elec-trical circuit coupling a source of signal energyto the input of the amplifying device; or involv-ing electrical characteristics of the source; orinvolving input electrical parameters of theamplifying device to which the signal input iscoupled.

(1) Note. Subject matter in which a sourceis claimed by name only as a specific artdevice, as for example, a microphone, isclassified with specific art device andnot with amplifiers. Subject matter in

which the source device may be broadlyclaimed, not by name, but by some dis-tinctive identifying feature thereof, aswhere the microphone source is claimedas a “means for converting sound sig-nals”, classification is not with amplifi-ers but with the distinctive art device.

(2) Note. The term “generator” or “oscilla-tor” in claims, where either appears as asource of signal energy without furtherqualification except an electrical charac-teristic such as impedance, reactanceetc., is treated as a generalized source ofsignal energy, and classification is withamplifiers. Where specific details of thegenerator or oscillator are claimed, clas-sification is with the type of generatorestablished in the claims or with oscilla-tors in Class 331, Oscillators.

(3) Note. Amplifier subject matter disclos-ing an interstage coupling but whereinonly the input coupling to the succeedingstage is claimed and no interstage cou-pling or details to establish such cou-pling are claimed, is not classified in thisand indented subclasses. See the searchthis class, subclass notes below for Inter-stage Coupling.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65+, for input coupling involving structure

of any of the input circuit elements.74, for plural inputs to series energized

tubes.106, for amplifiers having feedback in

series with the input source.108, for input coupling which may include

a potentiometer therein common tothe signal and feedback paths.

116, for amplifiers with balanced inputinvolved in balanced-to-unbalancedcircuits.

117, for amplifiers with unbalanced inputinvolved in unbalanced-to-balancedcircuits.

122, for push-pull amplifiers with signifi-cant input coupling.

143, for amplifiers having thermallyresponsive impedance which may bein the input coupling.


1April 2009

144, for amplifiers with variable imped-ance controlled by separate controlpath which may be in the input cou-pling.

147, for plural signal inputs.157+, appropriate subclasses for input cou-

pling involved in interstage couplingparticularly subclasses 158+ and160+. See (3) Note under this sub-class above.

192, for output coupling networks.252+, for semiconductor amplifiers with

plural inputs.275, and 301, for semiconductor amplifier

devices having balanced coupling.


works, subclasses 24+ for passivecoupling networks for wave transmis-sion generally.

338, Electrical Resistors, appropriate sub-classes for the structure of rheostats orresistors which may be used in inputcoupling.

186 To cathode :This subclass is indented under subclass 185.Subject matter wherein the input signal is cou-pled to the cathode of a vacuum tube amplify-ing device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:88+, and 91+, for signal feedback to a cath-

ode circuit, particularly subclass 89for cathode-cathode coupling betweenadjacent stages.

119, for push-pull amplifiers involvingcoupling to the cathode.

156, involving coupling directly betweencathode and grid.

158+, for interstage coupling to the cathode.250+, for subject matter including semicon-

ductor device input coupling to emit-ter, which may be the dual oranalogue of an input coupling circuitto the cathode electrode of a vacuumtube amplifying device.

187 D.C. coupled:This subclass is indented under subclass 186.Subject matter wherein the input coupling net-work has a D.C. conductive path from the

source of signal energy to the cathode inputelectrode of the amplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:159, for D.C. interstage coupling to the

cathode of a vacuum tube amplifyingdevice.

188 Transformer coupled:This subclass is indented under subclass 185.Subject matter in which the input circuitincludes a transformer which couples the signalenergy from the signal source to the amplifierdevice.

SEE OR SEARCH THIS CLASS, SUB-CLASS:120, for interstage coupling between push-

pull stages which may involve trans-former coupling.

122, for input coupling for push-pullamplifiers which may involve trans-former coupling.

154, for transformer coupling which maybe involved in a cascaded amplifierwith different interstage couplings.

165+, involving interstage transformer cou-pling.

195+, for output transformer coupling.


works, subclasses 177+ for passivewave transmission transformer cou-pling circuits generally.

189 With additional impedance connected to"P" or "S" circuits:This subclass is indented under subclass 188.Subject matter wherein additional impedancewhich may be capacitive, inductive, or resistiveis included in either the primary or secondarywinding circuit of the input coupling trans-former.

SEE OR SEARCH THIS CLASS, SUB-CLASS:167, for interstage transformer coupling,

with additional impedance in the pri-mary or secondary winding circuit.

195+, for output transformer couplingincluding additional impedance in the


April 2009

primary or secondary winding of thetransformer coupling network.

190 With transformer structure:This subclass is indented under subclass 188.Subject matter involving the structure of thetransformer in the input coupling circuit.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65+, for structure of amplifier system ele-

ments other than that of the trans-former.

170, for interstage transformer couplingwith shielding.

171, for interstage transformer structure.197, for structure of the transformer in the

output coupling.


classes for transformer structure, perse.

191 D.C. coupled:This subclass is indented under subclass 185.Subject matter wherein the input coupling cir-cuit has a D.C. conductive path from the signalinput source to the signal input electrode of theamplifying device.




53+, for amplifiers having distributedparameter coupling means which mayhave a D.C. conductive path.

125, for plural amplifier channels involv-ing a D.C. and an A.C. amplifierchannel.

159, for interstage D.C. coupling to cath-ode.

161, for interstage D.C. coupling to screengrid or electrode other than controlgrid or cathode.

163, for D.C. interstage coupling from gridor between grid and anode.

173, for D.C. interstage coupling fromcathode.

181+, for D.C. interstage coupling.

187, for cathode input D.C. coupling.194, for D.C. coupling from cathode.198, for D.C. output coupling.

192 OUTPUT NETWORKS:This subclass is indented under the class defini-tion. Subject matter involving significantdetail or distinctive characteristics of the elec-trical circuit coupling the output signal fromthe amplifying device to a load for utilizingsuch signal; or involving electrical characteris-tics or vacuum tube parameters such as outputimpedance of the amplifying device or imped-ance of the load involved in such coupling.

(1) Note. Where the load is claimed, evenbroadly, or by name only as a specificelectrical art device, as for example, as aloudspeaker, classification is not in thisclass, but with the load art deviceclaimed. Where characteristics of theload device are claimed, which are pecu-liar to the disclosed electrical art deviceor to a specific type of electrical artdevice, classification is with the load artdevice established in the claim.

(2) Note. Subject matter wherein generalelectrical characteristics of the load areclaimed, as for example, “a load havinga variable impedance”, is classified inthis or indented subclasses.

(3) Note. Subject matter disclosing an inter-stage coupling and where only the outputcoupling of a preceding stage is claimed,is not classified in this and indented sub-classes, although the coupling is claimedto establish an output coupling orclaimed as an output coupling.

(4) Note. Subject matter wherein an ampli-fier combined with an oscillator as loadfor the amplifier are classified withamplifiers when the oscillator is claimedby name only. Where specific details ofthe oscillator are claimed classificationis elsewhere.

SEE OR SEARCH THIS CLASS, SUB-CLASS:53+, for distributed parameter type output

coupling.


1April 2009

65+, for output coupling involving struc-ture of any of the output network cir-cuit elements.

73, for plural outputs from series ener-gized tubes.

105, for output coupling involving feed-back from an impedance in series withthe output load.

108, for output coupling including a poten-tiometer therein common to the signaland feedback paths.

116, for unbalanced output coupling inamplifiers having balanced-unbal-anced coupling.

117, for balanced output coupling in ampli-fiers having unbalanced-balancedcoupling.

122, for output coupling from a push-pullamplifier.

143, for thermally responsive impedancewhich may be in the output coupling.

144+, for variable impedance which may bein the output coupling.

157+, for interstage coupling involving cou-pling from the output of an amplifierdevice particularly subclasses 162+for output coupling from grid orbetween grid and anode, subclass 168for transformer coupling from cath-ode, 172+ for other interstage cou-pling from the cathode.

185, for input coupling networks for ampli-fiers.

252+, for semiconductor amplifiers havingplural outputs.

275, and 301, for semiconductor amplifiershaving either balanced or unbalancedoutput.

SEE OR SEARCH CLASS:331, Oscillators, where specific details of

the oscillator are claimed.333, Wave Transmission Lines and Net-

works, subclasses 24+ for passivecoupling networks for wave transmis-sion in general.

193 From cathode:This subclass is indented under subclass 192.Subject matter, wherein the output signal iscoupled from the cathode electrode of a vac-uum tube amplifying device.


amplifiers which may have the outputcoupled from the cathode of a vacuumtube amplifying device.

88+, and 91, for signal feedback coupledfrom the cathode particularly subclass89 for cathode-cathode coupling ofadjacent stages.

117, for unbalanced-to-balanced couplingincluding phase splitters having cath-ode coupled output.

119, for push-pull amplifiers involvingcoupling from the cathode.

153, for cascaded amplifiers having pluralinterstage couplings of different char-acteristics.

156, for bootstrap coupling.168, for transformer interstage coupling

from the cathode.172+, for interstage coupling from the cath-

ode.250+, for semiconductor device emitter fol-

lower circuits, analogous to cathodefollower circuits.

293, and 296, for series energized cascadedsemiconductor amplifier deviceswhich may have the output coupledfrom an emitter electrode of a transis-tor.

194 D.C. coupled:This subclass is indented under subclass 193.Subject matter in which the output couplingnetwork has a D.C. conductive path from thecathode to the load.

SEE OR SEARCH THIS CLASS, SUB-CLASS:173, for D.C. coupling from the cathode

involved in interstage coupling.

195 Transformer coupled:This subclass is indented under subclass 192.Subject matter in which the output circuit net-work includes a transformer for coupling thesignal from the amplifier device to the load.


April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:120, and 122, for push-pull amplifiers

which may involve transformer outputcoupling.

154, for transformer coupling involved inplural diverse stages of a cascadedamplifier.

165+, involving interstage transformer cou-pling.

188+, for input transformer coupling.


works, subclasses 177+ for wavetransmission transformer coupling cir-cuits in general.

334, Tuners, subclasses 59+ and 61+ fortuners having a transformer in the res-onant circuit.

196 With additional impedance connected to"P" or "S" circuit:This subclass is indented under subclass 195.Subject matter where additional impedancewhich may be capacitive, inductive, or resistiveis included in the primary or secondary wind-ing circuit of the output coupling transformer.

SEE OR SEARCH THIS CLASS, SUB-CLASS:167, for interstage transformer coupling

with additional impedance in the pri-mary or secondary winding circuit.

189, for input transformer coupling withadditional impedance connected in theprimary or secondary winding circuit.

197 With transformer structure:This subclass is indented under subclass 195.Subject matter involving the structure of thetransformer in the output coupling circuit.

SEE OR SEARCH THIS CLASS, SUB-CLASS:65+, for structure of amplifier system ele-

ments other than that of the trans-former.

170, for interstage transformer couplingwith shielding.

171, for interstage transformer structure.190, for input transformer structure.


classes for transformer structure, perse.

198 D.C. coupled:This subclass is indented under subclass 192.Subject matter wherein the output couplingnetwork has a D.C. conductive path from theoutput electrode of the amplifying device to theload.




53+, for amplifiers having distributedparameter coupling means which mayhave a D.C. conductive path.

125, for plural amplifier channels involv-ing a D.C. and an A.C. amplifierchannel.

159, for interstage D.C. coupling to cath-ode.

161, for interstage D.C. coupling to screengrid or electrode other than controlgrid or cathode.

163, for D.C. interstage coupling from gridor between grid and anode.

173, for D.C. interstage coupling fromcathode.

181+, for D.C. interstage coupling.187, for cathode input D.C. coupling.191, for D.C. input coupling.194, for D.C. coupling from cathode.

199 WITH POWER OR BIAS VOLTAGE SUP-PLY:This subclass is indented under the class defini-tion. Subject matter in which the “source ofelectrical energy” controlled by the signalinput; or biasing means applied to the “ampli-fying device”, or the means to apply suchenergy or bias, such as the circuits throughwhich such source or bias is applied; or meansfor isolating such source or biasing means fromthe signal path or other amplifier circuits (byfilters, isolating resistors, or other means), issignificantly claimed, and which subject matter


1April 2009

is not provided for in any of the previous sub-classes.

(1) Note. Merely claiming power supplysource or biasing means by name only orbroadly without significant detail or dis-tinctive characteristics is insufficient forclassification in this and indented sub-classes.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4, for maser type amplifying devices.5, for solid element wave propagating

amplifying devices.6, for Hall effect type means.7, for capacitive amplifying devices.8, for saturable reactor type amplifying

devices.41, for gas or vapor tube amplifying

devices.42, for secondary electron emission tube

amplifying device.43, for traveling wave type tube.44+, for electron beam tube amplifying

device.47+, for magnetically influenced discharge

devices, (e.g., magnetrons).49, for vacuum tube having distributed

parameter impedance characteristics.58, for rotating dynamoelectric amplify-

ing devices.60, for magnetostrictive type amplifying

devices.61+, for restrictive and magnetoresistive

type amplifying devices.63, for significant power supply or bias-

ing means combined with an amplify-ing device and magnetic means whichcontrols the energy of said power sup-ply or biasing means, or when a mag-netic means is involved in some othermanner in the structure of an amplify-ing device combined with significantpower supply or biasing means.

64, for space charge grid tubes biased tooperate as such.

70+, for series energized vacuum tubeamplifiers and 18 for series energizedsemiconductor amplifiers.

113, for polyphase power supply.114+, for unrectified A.C. power supply.

123, for amplifiers including a push-pullstage having significant bias or powersupply means.

127+, for amplifiers with means to controlthe bias or power supply voltage.

142, for cathode self-biasing circuits.149, for hum elimination by introduction

of the hum component in the signalpath in opposed phase.

296, and 297, for semi-conductor typeamplifying devices when combinedwith significant power supply or biasmeans or involving related circuitry.


nection Systems, subclasses 149+ formiscellaneous “power pack'” systems.

315, Electric Lamp and DischargeDevices: Systems, subclasses 91+ forcathode or cathode heater includinganode supply circuit but not includingany grid biasing circuit.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 530+ for miscellaneouscircuits combined with power supplyor bias means.

329, Demodulators, appropriate sub-classes for demodulators with particu-lar power supply.


200 For plural stage amplifier:This subclass is indented under subclass 199.Subject matter where the power supply or biasmeans is for an amplifier comprising two ormore stages of amplification.


devices which may involve powersupply or bias means.

88+, 92, and 98+, for cascaded signal feed-back amplifiers which may involvepower supply or bias means.

123, for push-pull amplifiers, which maybe cascaded, having significant biasor power supply means.

124, for plural amplifier channels whichmay involve cascaded amplifiers hav-


April 2009

ing significant power or bias supplymeans.

133, for different bias controls for differentstages of a cascaded amplifier.

150, for cascaded amplifiers with differentcharacteristics which may be differentbias means or voltages.

152+, for cascaded amplifiers, differentlycoupled between stages, which mayinvolve circuitry for the bias or powersupply means also.

157+, for amplifiers with interstage couplingcircuits which may involve circuitryfor the bias or power supply meansalso.

296+, for plural stage semiconductor ampli-fiers involving bias or power supplycircuitry.

201 Filamentary cathodes heated by anode cur-rent or anode supply source:This subclass is indented under subclass 200.Subject matter where the filamentary cathodesof at least one vacuum tube amplifying deviceof the plural stage amplifier derives its electri-cal heating supply either from the anode oranode power supply of one vacuum tube ampli-fying device stage of the plural stage amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:115, for amplifiers having unrectified A.C.

power supplied to a filamentary cath-ode (directly heated type).

205, for similar subject matter for a fila-mentary cathode also involving powersupply or bias means for an inputelectrode.

206, for power supply or bias meansapplied to a filamentary cathode(directly heated type), generally.


Devices: Systems, subclasses 94+ forpower supply or power supply circuitfor cathode filament or cathode heatercircuit with or without anode supplybut not including grid biasing supply.

202 For anode:This subclass is indented under subclass 199.Subject matter wherein the “source of electricalenergy”, biasing means, the circuit or means

for supplying such electrical energy or biasvoltage, or isolating means for such source orbias means supplies the anode of a vacuumtube amplifying device or isolates such supplyfor the anode from other parts of the amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:70+, for series energized amplifiers.128, for control of bias or power supply

voltage with control means in anodeor screen grid circuit.

157+, 185+ and 192+, appropriate sub-classes thereunder for impedancesfrom the power source to anodeinvolved in interstage, input, and out-put coupling respectively.

293+, for series energized semiconductoramplifying devices.

203 And input electrode:This subclass is indented under subclass 202.Subject matter where additional bias supply orisolating means are furnished for an input elec-trode of an amplifying device.

(1) Note. Input electrode refers to any elec-trode to which the electrical signal inputis applied, usually the control grid physi-cally next to the cathode, and the cathodewhich is, usually, also common to theinput and output circuits of the amplifier,the anode being an output electrode.

(2) Note. Cathode self-biasing circuitswhere the bias is established by the flowof plate current through the cathodeimpedance are not classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:142, for cathode self-biasing circuits where

the bias is established by the flow ofplate current through the cathodeimpedance.

204 For input electrode:This subclass is indented under subclass 199.Subject matter wherein the bias supply or iso-lating means is furnished to or for an inputelectrode of a vacuum tube amplifying device.

(1) Note. Input electrode refers to any elec-trode to which the electrical signal input


1April 2009

is applied, usually the control grid physi-cally next to the cathode and the cathodewhich is usually, also common to theinput and output circuits of the amplifier,the anode being an output electrode. Ingrounded grid amplifiers the relationshipof cathode and anode as described aboveis, of course, usually reversed.

(2) Note. Cathode self-biasing circuitswhere the bias is established by the flowof plate current through the cathodeimpedance are not classified herein.

SEE OR SEARCH THIS CLASS, SUB-CLASS:142, for cathode self-biasing circuits where

the bias is established by the flow ofplate current through the cathodeimpedance.

157+, 185+ and 192+, for impedances in theinput electrode bias circuit involved ininterstage, input, or output coupling,respectively.

205 And filamentary cathode:This subclass is indented under subclass 204.Subject matter wherein power supply, biasmeans or isolating means are supplied to thefilamentary cathode of the vacuum tube ampli-fying device, as input electrode; and/or as cath-ode heating electrical current supply to thedirectly heated filamentary cathode.


power supplied to a filamentary cath-ode.

127, for control of emission of a cathodeelectrode.

201, for power supply bias means for cath-ode filaments in a plural stage ampli-fier heated by the anode current or bycurrent from the anode supply source.

206, for power supply for a filamentarycathode generally.


Devices: Systems, subclasses 94+ forpower supply or power supply circuitfor cathode filament or cathode heater

circuit with or without anode supplybut not including grid biasing supply.

206 For filamentary cathode:This subclass is indented under subclass 199.Subject matter which may include the heatercurrent supply for a filamentary cathode of avacuum tube amplifying device not classifiedin any preceding subclass.


power supplied to a filamentary cath-ode.

127, for control of emission of a cathodeelectrode.

201, for power supply bias means for cath-ode filaments in a plural stage ampli-fier heated by the anode current or bycurrent from the anode supply source.

205, for similar subject matter for a fila-mentary cathode also involving powersupply or bias means for an inputelectrode.


Devices: Systems, subclasses 94+ forpower supply or power supply circuitfor cathode filament or cathode heatercircuit with or without anode supplybut not including grid biasing supply.

207 MISCELLANEOUS:This subclass is indented under the class defini-tion. Subject matter not provided for in any ofthe subclasses above.

250 WITH SEMICONDUCTOR AMPLIFY-ING DEVICE (E.G., TRANSISTOR):This subclass is indented under the class defini-tion. Subject matter in which the amplifyingdevice is a semiconductor.

(1) Note. Semiconductors are those materi-als which have a specific resistance, forexample, of the order of that of germa-nium, silicon, selenium, etc. Subjectmatter including insulators which are inoperation reduced to specific resistancevalues of the aforesaid range, by alpha orelectron bombardment, heat or othermeans so they act in the circuit, broadly,


April 2009

as semiconductors, are classified in thisor appropriate indented subclasses.

(2) Note. For specific types of amplifierdevices in amplifiers, which may includea semiconductor material, see the perti-nent subclass for the particular semicon-ductor device involved in this class.

(3) Note. For vacuum tube amplifier device,amplifier circuits similar or related tosemiconductor amplifier device circuits,see below the appropriate subclass andindented subclasses for such circuit.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for combined plural diverse amplify-

ing-type devices, where one of theamplifying devices is of the semicon-ductor type.

4, for master-type amplifying deviceswherein the master excited substanceis a semiconductor.

4.9, for parametric semiconductor amplifi-ers.

5, for solid element wave propagatingamplifying devices wherein the solidelement is a semiconductor.

6, for Hall effect-type semiconductoramplifying devices wherein the Halleffect material is a semiconductor.

7, for capacitive amplifying devices,some of which may have semiconduc-tor properties.

9, for amplifier systems with periodicswitching input-output comparison ofsignal which may have a semiconduc-tor amplifying device.

10, for modulator-demodulator amplifiersystems which may have semiconduc-tor amplifier devices.

11, for amplifiers having D.C. reinsertioncircuits which may include a semicon-ductor amplifying device.


Transistors, Solid-State Diodes),appropriate subclasses integrated cir-cuit structure with active solid-statedevices, especially subclasses 115,123, and 157 through 161 for regener-ative type devices with amplification

means, and subclasses 446 and 499+for integrated circuit devices withelectrically isolated components.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for miscella-neous nonlinear conductor device(e.g., transistor) circuits. See searchnotes.

329, Demodulators, appropriate sub-classes for demodulators utilizingtransistor elements.

361, Electricity: Electrical Systems andDevices, for transistor circuits withelectric relays or electromagneticloads.

438, Semiconductor Device Manufactur-ing: Process, appropriate subclass formethods of making semiconductorelectrical devices.

251 Including class D amplifier:This subclass is indented under subclass 250.Subject matter including an amplifier whichutilizes switching-mode techniques.

SEE OR SEARCH THIS CLASS, SUB-CLASS:9, and 10, for amplifiers which may use

switching amplifiers as a subcircuitthereof.

207, for amplifiers using switching-modetechniques.


linear Devices, Circuits, and Systems, subclasses 365+ for transistors used ina switching mode.

252 Including differential amplifier:This subclass is indented under subclass 250.Subject matter including an amplifier havingtwo similar input circuits so connected thatthey respond to the difference between twovoltages or currents, but effectively suppresslike voltages or currents.

SEE OR SEARCH THIS CLASS, SUB-CLASS:69, for tube-type amplifiers functioning in

a differential mode.


1April 2009

253 Having field effect transistor:This subclass is indented under subclass 252.Subject matter wherein a field effect transistor(FET) is utilized in the circuit with the differ-ential amplifier.

(1) Note. A field effect transistor (FET) is asemiconductor device in which the resis-tance between two terminals, the sourceand drain, depends on a field producedby a voltage applied to the third terminal,the gate.

(2) Note. The field may modulate a deple-tion region, as in a junction FET, or itmay cause a conductivity change in achannel, as in a MOS-FET.

SEE OR SEARCH THIS CLASS, SUB-CLASS:264, for FET in combination with push-

pull utilized in complementary sym-metry.

269, for FET in combination with push-pull amplifier.

277, for FET in other transistor amplifiers.300, for FET in combined diverse-type cir-

cuit.


linear Devices, Circuits, and Systems, subclass 581 for field-effect transis-tors used in miscellaneous circuits.

254 Having gain control means:This subclass is indented under subclass 252.Subject matter including circuitry which con-trols the amplification of the applied signal.

(1) Note. Gain is any increase in powerwhen a signal is transmitted from onepoint to another.

SEE OR SEARCH THIS CLASS, SUB-CLASS:278+, for other semiconductor amplifiers

with gain control.

SEE OR SEARCH CLASS:348, Television, subclasses 645+ for color

television circuits having gain control.

255 Having push-pull amplifier stage:This subclass is indented under subclass 252.Subject matter including an amplifier whichhas two identical signal branches connected soas to operate in phase opposition and with inputand output connections, each balanced toground.

SEE OR SEARCH THIS CLASS, SUB-CLASS:77, for push-pull amplifiers with feedback

neutralization.81+, for push-pull amplifiers with feed-

back.118+, for vacuum tube amplifiers including

a push-pull stage.262, for push-pull amplifiers not in combi-

nation with differential amplifiers.

256 Having temperature compensation means:This subclass is indented under subclass 252.Subject matter wherein temperature compen-sating means are utilized to protect or stabilizethe amplifying device from changes in theambient temperature.

(1) Note. Changes in the ambient tempera-ture can change the operating character-istics of the amplifier and therebychange the output signal.

SEE OR SEARCH THIS CLASS, SUB-CLASS:266, for temperature compensation in com-

plementary push-pull amplifiers.272, for temperature compensation in a

push-pull amplifier.289, for temperature compensation in other

transistor amplifiers.

257 Having current mirror amplifier:This subclass is indented under subclass 252.Subject matter wherein an amplifier having again which is substantially independent of theindividual common emitter forward currentgains of its component transistor, is utilized.

SEE OR SEARCH THIS CLASS, SUB-CLASS:288, for current mirror amplifier in other



April 2009

258 Having common mode rejection circuit:This subclass is indented under subclass 252.Subject matter wherein means are utilizedwhich ignore a signal that appears simulta-neously and in phase at both input terminals.

SEE OR SEARCH THIS CLASS, SUB-CLASS:69, for differential amplifiers which may

include a common mode rejection cir-cuit.

259 Having D.C. feedback bias control for stabi-lization:This subclass is indented under subclass 252.Subject matter including a feedback circuit fordirect currents for the purpose of operatingpoint stabilization.


for input-output comparison includingthose having feedback circuits fordrift correction, etc.

270, for D.C. feedback in push-pull com-plementary symmetry amplifiers.

290, for D.C. feedback in other transistoramplifiers.

260 Having signal feedback means:This subclass is indented under subclass 252.Subject matter wherein a portion of the electri-cal signal output energy is applied to the inputof the amplifier.

(1) Note. There is a shared impedance forthe input and output circuits involved.

(2) Note. The amplifier in this subclass maybe any stage or group of stages of a cas-caded amplifier.


input-output comparison includingthose with feedback circuits.

75+, appropriate subclasses for vacuumtube signal feedback amplifiers.

265, for signal feedback in complementarypush-pull amplifiers.

271, for signal feedback in push-pullamplifier.

282, for signal feedback in gain control cir-cuit.

291, for feedback in other transistor ampli-fiers.

261 Having particular biasing arrangement:This subclass is indented under subclass 252.Subject matter with specific details or distinc-tive characteristics of the biasing meansapplied to the amplifying device.

(1) Note. Merely claiming biasing means orbias filter by name only, or broadly with-out significant detail or distinctive char-acteristics, is insufficient forclassification in this subclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for particular biasing in other amplifi-

ers.267, for particular biasing in combination

with complementary symmetry.273, for particular biasing in combination

with a push-pull amplifier.285, for particular biasing in gain control

means.296, for particular biasing in other transis-

tor amplifiers.

262 Including push-pull amplifier:This subclass is indented under subclass 250.Subject matter including at least one push-pullamplifier.

(1) Note. See the Glossary in this class forthe definition of “Push-Pull Amplifier”.

SEE OR SEARCH THIS CLASS, SUB-CLASS:77, for push-pull amplifiers with feedback

neutralization.81+, for push-pull amplifiers with feed-

back.118+, for vacuum tube amplifiers including

a push-pull stage.255, for push-pull amplifiers in combina-

tion with differential amplifiers.


1April 2009

263 Having complementary symmetry:This subclass is indented under subclass 262.Subject matter wherein semiconductor devicesof opposite conductivity are utilized.

(1) Note. Complementary symmetry is anarrangement of NPN and PNP transistorsthat provide push-pull operation fromone input signal.

(2) Note. There are two complementarytypes of conductivity in semiconduc-tors: The N-type where conduction islargely by electrons; and the P-typewhere conduction appears to be largelycarried by positive charges (i.e., holes).In junction transistors which consist ofzones of more than one conductivitytype of semiconductor material, the con-ductivity is determined by the controlzone so that the PNP-type junction tran-sistor is equivalent to an N-type semi-conductor body or an N-type pointcontact semiconductor device and anNPN junction type similarly equivalentto a P-type of semiconductor device of asingle conductivity type of material.

264 And field effect transistor:This subclass is indented under subclass 263.Subject matter wherein a field effect transistor(FET) is utilized in the circuit.



SEE OR SEARCH THIS CLASS, SUB-CLASS:253, for FET in combination with differen-

tial amplifiers.269, for FET in combination with push-

pull amplifiers.277, for field effect transistors in other


300, for field effect transistors in combineddiverse-type semiconductor devices.


linear Devices, Circuits, and Systems, subclass 581 for miscellaneous cir-cuits using field-effect transistors.

265 And feedback means:This subclass is indented under subclass 263.Subject matter wherein a portion of the ampli-fier stage output signal is returned to the inputof the amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:260, for signal feedback in differential

amplifiers.271, for signal feedback in push-pull

amplifiers.282, for signal feedback in gain control cir-

cuits.291, for signal feedback in other transistor

amplifiers.

266 And temperature compensation:This subclass is indented under subclass 263.Subject matter wherein temperature compen-sating means are utilized to protect or stabilizethe amplifying device from changes in theambient temperature.


SEE OR SEARCH THIS CLASS, SUB-CLASS:256, for temperature compensation in dif-

ferential amplifiers.272, for temperature compensation in a

push-pull amplifier.289, for temperature compensation in other


267 And particular biasing arrangement:This subclass is indented under subclass 263.Subject matter with specific details or distinc-tive characteristics of the biasing meansapplied to the amplifying device.


April 2009


SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for particular biasing in general.261, for particular biasing in combination

with a differential amplifier.273, for particular biasing in combination

with a push-pull amplifier.285, for particular biasing in gain control

circuits.296, for particular biasing not in combina-

tion in any of the aforementioned.

268 To eliminate crossover distortion:This subclass is indented under subclass 267.Subject matter wherein distortion which occursat the points of operation where the input sig-nals cross over the zero reference points iseliminated.

SEE OR SEARCH THIS CLASS, SUB-CLASS:274, for means to eliminate crossover dis-

tortion in noncomplementary, symme-try push-pull amplifiers.

269 Having field effect transistors:This subclass is indented under subclass 262.Subject matter wherein a field effect transistor(FET) is utilized in the circuit.



SEE OR SEARCH THIS CLASS, SUB-CLASS:253, for FET in combination with a differ-

ential amplifier.

264, for FET in complementary symmetryin push-pull.

277, for FET in other transistor amplifiers.300, for FET in combined diverse-type cir-

cuit.


linear Devices, Circuits, and Systems, subclass 581 for miscellaneous cir-cuits using field-effect transistors.

270 Having D.C. feedback bias control for stabi-lization:This subclass is indented under subclass 262.Subject matter with a feedback circuit fordirect currents, for the purpose of operatingpoint stabilization.

(1) Note. Included here are devices forcompensating for changes in tempera-ture, aging, etc., of the semiconductordevice, or devices which may includemeans such as bypass capacitors to elim-inate signal feedback.

(2) Note. This does not include a merebypassed emitter resistor unless D.C.derived therefrom is applied to anotherelectrode.



259, for D.C. feedback in combinationwith a differential amplifier.

290, for D.C. feedback in other transistoramplifiers.

271 Having signal feedback means:This subclass is indented under subclass 262.Subject matter wherein a portion of the electri-cal signal output energy is applied to the inputof the amplifier.


(2) Note. The amplifier of this subclass maybe any stage or group of stages of a cas-caded amplifier.


1April 2009




265, for feedback in complementary push-pull amplifiers.

282, for signal feedback in gain control cir-cuits.

291, for feedback in other transistor ampli-fiers.

272 Having temperature compensating means:This subclass is indented under subclass 262.Subject matter wherein temperature compen-sating circuits or devices are utilized to protector stabilize the semiconductor amplifyingdevices from changes in the ambient tempera-ture.

(1) Note. Changes in the ambient tempera-ture of a circuit's environment canchange the operating characteristics ofthe semiconductor amplifying deviceand thereby change the output signal.

SEE OR SEARCH THIS CLASS, SUB-CLASS:256, for temperature compensation in a dif-

ferential amplifier.266, for temperature compensation in com-

plementary push-pull amplifiers.289, for temperature compensation in other


273 Having particular biasing arrangement:This subclass is indented under subclass 262.Subject matter with specific details or distinc-tive characteristics of the biasing meansapplied to the amplifying device.

(1) Note. Merely claiming biasing means orbias filter by name only, or broadly with-out significant details or distinctive char-acteristics, is insufficient forclassification in this subclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for particular biasing in general.

261, for particular biasing in combinationwith a differential amplifier.

267, for particular biasing in combinationwith complementary symmetry.

285, for particular biasing in gain controlcircuits.

296, for particular biasing in other transis-tor amplifiers.

274 To eliminate crossover distortion:This subclass is indented under subclass 273.Subject matter wherein distortion which occursat the points of operation where the input sig-nals cross over the zero reference points iseliminated.

SEE OR SEARCH THIS CLASS, SUB-CLASS:268, for means to eliminate crossover dis-

tortion in complementary symmetry.

275 Having balanced to unbalanced circuitryand vice versa:This subclass is indented under subclass 262.Subject matter wherein one of the signal inputmeans or signal output means is coupled to orfrom the semiconductor amplifier by a bal-anced circuit, the other signal coupling meanscoupled to or from the semiconductor amplifierbalanced circuit.

(1) Note. For the definition of a “BalancedCircuit”, see the class definition, Glos-sary.

SEE OR SEARCH THIS CLASS, SUB-CLASS:301, for balanced to unbalanced circuits

and vice versa in other transistoramplifiers.

276 Having transformer:This subclass is indented under subclass 262.Subject matter wherein a transformer isincluded in the circuit.

(1) Note. The transformer can be in theinput, output, interstage, or any combi-nation of the aforementioned.

277 Including field effect transistor:This subclass is indented under subclass 250.Subject matter wherein a field effect transistor(FET) is utilized in the amplifier circuit.


April 2009



SEE OR SEARCH THIS CLASS, SUB-CLASS:253, for FET in differential amplifiers.264, for FET in combination with push-

pull utilized in complementary sym-metry.

269, for FET in combination with push-pull amplifiers.

300, for FET in combined verse-type cir-cuit.

278 Including gain control means:This subclass is indented under subclass 250.Subject matter including circuitry which con-trols the amplification of the applied signal.


control means.96, for feedback amplifiers combined

with control of bias voltage of a signalamplifier.

123, for push-pull amplifiers having signif-icant power or bias supply circuitsincluding those with bias controlmeans.

127+, for amplifiers with control of powersupply or bias voltage.


144+, for amplifiers having a variableimpedance in the signal path varied bya separate control path.

155+, for amplifiers having unicontrol ofcoupling or associated circuits includ-ing unicontrol of signal input or out-put potentiometers, etc..

157+, 185+ and 192+, for interstage input oroutput coupling, respectively, includ-

ing variable impedance means in suchcoupling.

254, for gain control means in combinationwith a differential amplifier.


works, particularly subclasses 14, 16,and 17.1 for combined amplifier com-pressor and expander means, pilotcontrolled means, and automaticallycontrolled systems, respectively; sub-classes 24+ for coupling networkswhich may include signal amplitudecontrol means; subclasses 213+ fornegative resistance and/or reactancenetworks of the active element type;and subclass 81 for attenuators.

455, Telecommunications, subclasses232.1+ for volume control, especiallysubclasses 234.1+ for automatic vol-ume control.

279 And significant control voltage developingmeans:This subclass is indented under subclass 278.Subject matter including specific details or dis-tinctive characteristics of the gain controldeveloping means.

SEE OR SEARCH THIS CLASS, SUB-CLASS:127+, 143 and 144+, for other amplifiers

having gain control systems whichmay have significant control voltagedeveloping means.

SEE OR SEARCH CLASS:455, Telecommunications, subclasses

232.1+ for receivers which may havesignificant control voltage develop-ing means as part of a gain controlsystem.

280 With delay means:This subclass is indented under subclass 279.Subject matter including circuit means whichimpart to the control voltage, a minimum levelat which the control voltage developing meansbegins to function.


1April 2009

SEE OR SEARCH THIS CLASS, SUB-CLASS:127+, 143 and 144+, for gain-controlled

amplifiers which may have delaymeans.


242.1+ for gain-controlled receiverswhich may have delay means.

281 With time constant means:This subclass is indented under subclass 279.Subject matter including a circuit for filteringthe control voltage, and wherein specificdetails or distinctive characteristics of such cir-cuit are claimed.

SEE OR SEARCH THIS CLASS, SUB-CLASS:127+, 143 and 144+, for amplifiers which

may include time-constant means inthe control voltage path thereof.


239.1+ for gain-controlled receiverswhich may include time-constantmeans in the control voltage paththereof.

282 Having feedback means acting as variableimpedance:This subclass is indented under subclass 278.Subject matter including a feedback means act-ing as a variable impedance to control the gainof the amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:86, for amplifiers having variable imped-

ance in feedback path varied by sepa-rate control path.

283 Having emitter degeneration:This subclass is indented under subclass 282.Subject matter including a feedback means act-ing as a variable impedance in the commonelectrode of the amplifier to control the gain ofthe amplifier.

SEE OR SEARCH THIS CLASS, SUB-CLASS:95, for amplifiers having nonlinear

impedance means in the cathodeimpedance feedback path.

284 Having attenuation means in signal trans-mission path:This subclass is indented under subclass 278.Subject matter having attenuation means in sig-nal transmission path that controls the gain ofthe amplifier.


control means.143, for amplifiers having thermally

responsive means.144+, for amplifiers having variable imped-

ance for signal channel controlled byseparate control path.

SEE OR SEARCH CLASS:455, Telecommunications, subclass 249.1

for gain-controlled receiver havingvariable impedance in the control cir-cuit.

285 Having particular biasing means:This subclass is indented under subclass 278.Subject matter having specific details or dis-tinctive characteristics of a biasing means forapplying a biasing voltage to the amplifyingdevice.


SEE OR SEARCH THIS CLASS, SUB-CLASS:127+, for amplifiers with control of power

supply or bias voltage.199+, for particular biasing in other amplifi-

ers.261, for particular biasing in differential

amplifiers.267, for particular biasing in combination

with complementary symmetry.


April 2009

273, for particular biasing in combinationwith a push-pull amplifier.

285, for particular biasing in gain controlcircuits.

296, for particular biasing in other transis-tor amplifiers.

286 Including distributed parameter-type cou-pling:This subclass is indented under subclass 250.Subject matter including coupling meanswhich has both distributive capacitance anddistributive inductance at high frequencies.

SEE OR SEARCH THIS CLASS, SUB-CLASS:53+, for amplifiers having distributed-type

coupling.

SEE OR SEARCH CLASS:331, Oscillators, subclasses 56+ for oscil-

lators having distributed parameterresonator.

333, Wave Transmission Lines and Net-works, subclasses 219+ for distrib-uted parameter resonator, and sub-classes 236+ for long lines havingdistributed parameters.

287 Of diode type:This subclass is indented under subclass 286.Subject matter including amplifying means ofthe diode type.

SEE OR SEARCH CLASS:331, Oscillators, subclass 107 for diode-

type oscillators.

288 Including current mirror amplifier:This subclass is indented under subclass 250.Subject matter wherein an amplifier having again which is substantially independent of theindividual common emitter forward currentgains of its component transistor is utilized.

SEE OR SEARCH THIS CLASS, SUB-CLASS:257, for current mirror amplifiers in com-

bination with differential amplifiers.


linear Devices, Circuits, and Systems, subclasses 530+ for miscellaneoustransistor circuits used for power sup-ply or bias regulation.

289 Including temperature compensationmeans:This subclass is indented under subclass 250.Subject matter wherein temperature compen-sating means are utilized to protect or stabilizethe amplifying device from changes in theambient temperature.


SEE OR SEARCH THIS CLASS, SUB-CLASS:256, for temperature compensation in a dif-

ferential amplifier.266, for temperature compensation in com-

plementary push-pull amplifiers.272, for temperature compensation in a

push-pull amplifier.

290 Including D.C. feedback bias control for sta-bilization:This subclass is indented under subclass 250.Subject matter with feedback circuit for directcurrents, for the purpose of operating point sta-bilization as compensating for changes in tem-perature, aging, etc., of the semiconductordevice, or devices, which may include meanssuch as bypass capacitors to eliminate signalfeedback.

(1) Note. This does not include a merebypass emitter resistor unless D.C.derived therefrom is applied to anotherelectrode.



97, for amplifiers including D.C. path forsignal feedback.


1April 2009

259, for D.C. feedback in differentialamplifiers.

270, for D.C. feedback in push-pull com-plementary symmetry amplifiers.

291 Including signal feedback means:This subclass is indented under subclass 250.Subject matter wherein a portion of the electri-cal signal output energy is applied to the inputof the amplifier.


(2) Note. The amplifier of this subclass maybe any stage or group of stages of a cas-caded amplifier.




260, for signal feedback in differentialamplifiers.

265, for feedback in complementary push-pull amplifiers.

271, for signal feedback in push-pullamplifiers.

282, for signal feedback in gain control cir-cuits.

292 Having compensation for interelectrodeimpedance: This subclass is indented under subclass 291.Subject matter wherein signal feedback meansare provided for, compensating for, or nullify-ing the undesirable feedback caused by any ofthe internal interelectrode impedances of thesemiconductor amplifying device.

SEE OR SEARCH THIS CLASS, SUB-CLASS:76+, for neutralization through compensa-

tion by signal feedback of the effectsof interelectrode impedance in vac-uum tube amplifiers.

293 Having negative feedback:This subclass is indented under subclass 291.Subject matter wherein the signal feedbackwhich is superimposed on the input signal has

at least one component thereof opposite inphase to the input signal.

SEE OR SEARCH THIS CLASS, SUB-CLASS:75+, for signal feedback in other amplifi-

ers.

294 Having frequency responsive means orphase shift means in the feedback path:This subclass is indented under subclass 291.Subject matter having frequency-responsivemeans or phase-shift means in the feedbackpath that causes corresponding changes inamplifier gain.

SEE OR SEARCH THIS CLASS, SUB-CLASS:107, and 109, for amplifiers having fre-

quency- or phase-responsive means inthe feed-back path.


linear Devices, Circuits, and Systems, subclasses 113+ for miscellaneousfrequency control, subclasses 231+for a phase shift of less than an inputsignal period, subclasses 2+ for phasediscriminating without subsequentcontrol, and subclasses 39+ for fre-quency discriminating without subse-quent control.

295 Including plural amplifier channels:This subclass is indented under subclass 250.Subject matter having more than one signaltransmission path, each of which contains anamplifier (e.g., plural inputs or plural outputs).

SEE OR SEARCH THIS CLASS, SUB-CLASS:84, for signal feedback amplifiers having

plural channels.124+, for amplifiers having plural amplifier

channels.147, for amplifiers having plural separate

inputs.148, for amplifiers having plural separate

outputs.


April 2009

296 Including particular biasing arrangement:This subclass is indented under subclass 250.Subject matter with specific details or distinc-tive characteristics of the biasing meansapplied to the amplifying device.

(1) Note. Merely claiming biasing meansor bias filter by name only, or broadlywithout significant detail or distinctivecharacteristics, is sufficient for classifi-cation in this subclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for particular biasing in other amplifi-

ers.261, for particular biasing in differential

amplifiers.267, for particular biasing in combination

with complementary symmetry.273, for particular biasing in combination

with push-pull amplifier.285, for particular biasing in signal ampli-

tude control.

297 Including particular power supply circuitry:This subclass is indented under subclass 250.Subject matter including specific details or dis-tinctive characteristics of the source of electri-cal energy applied to the semiconductoramplifying device.

(1) Note. This includes means to apply suchenergy source, the circuits throughwhich such source is applied, and meansfor isolating such source from the signalpath or other amplifier circuits.

(2) Note. Merely claiming power supplysource by name only, or broadly withoutsignificant detail or distinctive character-istics, is insufficient for classification inthis subclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:199+, for amplifiers generally involving bias

or power supply. See the search notesunder subclass 199.

298 Including protection means:This subclass is indented under subclass 250.Subject matter including circuits or devices forprotecting the amplifying means.

SEE OR SEARCH THIS CLASS, SUB-CLASS:207+, for amplifiers having protection cir-

cuitry.

299 Including combined diverse-type semicon-ductor device:This subclass is indented under subclass 250.Subject matter including plural semiconductordevices and at least one semiconductor devicewhich is different in its physical characteristicsor in materials, and which also amplifies thesignal.

(1) Note. Materials which may be a diode ofthe nonamplifying type, or which may bean additional signal carrier semicon-ductor amplifying device including anamplifier not previously provided for inthis schedule.

SEE OR SEARCH THIS CLASS, SUB-CLASS:94, and 110, for vacuum tube feedback

amplifiers having nonlinear imped-ance elements.

138, and 140, for amplifiers having a recti-fier, which may be a semiconductordiode, in a bias control circuit for theinput or gain control electrode.

143, for vacuum tube amplifiers having athermally responsive impedance.

144+, for vacuum tube amplifiers having aseparately controlled variable imped-ance in the signal path, which may bea semiconductor.

164, for vacuum tube amplifiers with adiode in the interstage coupling whichmay be a semiconductor.

174, for a piezoelectric crystal or electro-mechanical transducer broadly in theinterstage coupling of a vacuum tubeamplifier.

183, for vacuum tube amplifiers havingD.C. interstage coupling with a non-linear device therein.


1April 2009

300 Bipolar or unipolar (FET):This subclass is indented under subclass 299.Subject matter wherein the additional semicon-ductor device may be a bipolar or unipolartransistor.

SEE OR SEARCH THIS CLASS, SUB-CLASS:253, for field effect transistor (FET) in

combination with a differential ampli-fier.

264, for FET in combination with comple-mentary symmetry push-pull amplifi-ers.

269, for FET in combination with otherpush-pull amplifiers.

277, for other field effect transistors.


linear Devices, Circuits, and Systems, subclass 581 for miscellaneous FETcircuits.

301 Including balanced to unbalanced circuitsand vice versa:This subclass is indented under subclass 250.Subject matter wherein one of the signal inputmeans or signal output means is coupled to orfrom the semiconductor amplifier by a bal-anced circuit, the other signal coupling meanscoupled to or from the semiconductor amplifierunbalanced circuit.

(1) Note. For the definition of a “BalancedCircuit”, see the Glossary in this class.

SEE OR SEARCH THIS CLASS, SUB-CLASS:275, for balanced to unbalanced circuits in

push-pull amplifiers.

302 Including frequency-responsive means inthe signal transmission path:This subclass is indented under subclass 250.Subject matter including frequency-responsivemeans in the signal transmission path thatcauses corresponding changes in the amplifiergain.

SEE OR SEARCH THIS CLASS, SUB-CLASS:157+, 185+ and 192+, for interstage input or

output coupling, respectively, includ-ing variable impedance means in suchcoupling.

294, having frequency-responsive meansor phase-shift means in the feedbackpath.


linear Devices, Circuits, and Systems, subclasses 113+ for miscellaneousfrequency control, subclasses 231+for a phase shift of less than an inputsignal period, subclasses 2+ for phasediscriminating without subsequentcontrol, and subclasses 39+ for fre-quency discriminating without subse-quent control.

333, Wave Transmission Lines and Net-works, subclasses 24+ for frequencyor phase sensitive circuits in wavetransmission lines and networks.

303 Including an active device in the filtermeans:This subclass is indented under subclass 302.Subject matter including a transistor or activediode in the filter network.

SEE OR SEARCH THIS CLASS, SUB-CLASS:107, 109 and 294, for circuits having fre-

quency-responsive means or phase-shift means in the feedback path.


linear Devices, Circuits, and Systems, subclasses 552+ for miscellaneouscircuits suppressing an unwanted sig-nal using an active filter.

333, Wave Transmission Lines and Net-works, subclasses 24+ for frequencyor phase sensitive circuits in wavetransmission lines and networks.


April 2009

304 And equalizing means:This subclass is indented under subclass 302.Subject matter including a network connectedto a line to correct or control its transmissionfrequency characteristics.


works, subclass 28 for equalizers usedin wave transmission lines and net-works.

305 And tuning means:This subclass is indented under subclass 302.Subject matter including a manually adjustablefrequency selecting means.

SEE OR SEARCH CLASS:334, Tuners, appropriate subclasses for

tuning circuits.455, Telecommunications, subclasses 120+

for transmitters having tuning means;and subclasses 150.1+ for receivershaving tuning means.

306 And bandpass, broadband (e.g., wideband),or sidepass means:This subclass is indented under subclass 302.Subject matter including means which deter-mines the range of the frequencies of theapplied signal that will be amplified.


188.1+ for selectable band receivers.

307 Integrated circuits:This subclass is indented under subclass 250.Subclass matter under having a combination ofinterconnected elements inseparably associatedon or within a continuous substrate.

(1) Note. If a claimed preferred embodi-ment of a patent application includesdetails of means to apply a variable elec-trical signal to an IC amplifying device,or details of means to utilize the outputof an IC amplifying device, that applica-tion is properly classified in this sub-class.

(2) Note. If, however, a claimed preferredembodiment of a patent application is

limited to details of an IC amplifyingdevice, without details of the input oroutput (utilization) means, or the input oroutput (utilization) means are recited inname only, then the application is prop-erly classified outside this class.


Transistors, Solid-State Diodes),appropriate subclasses for activesolid-state devices, especially sub-classes 115, 123, and 162-166 whichare directed to devices involvingamplification. See the (2) Note above.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 564+ for miscellaneouscircuits which are integrated.

308 Including atomic particle or radiant energyimpinging on a semiconductor:This subclass is indented under subclass 250.Subject matter in which the amplifying devicesemiconductor body is subjected to radiantenergy which may be in the form of light, free(unrestrained) electromagnetic energy, gammarays, etc.., or atomic particle bombardment,such as alpha or beta rays, etc..

(1) Note. If a claimed preferred embodi-ment of a patent application includesdetails of means to apply a variable elec-trical signal to an IC amplifying device,or details of means to utilize the outputof an IC amplifying device, that applica-tion is properly classified elsewhere inthis class (330).

(2) Note. If, however, a claimed preferredembodiment of a patent application islimited to details of an IC amplifyingdevice without details of the input oroutput (utilization) means, or the input oroutput (utilization) means are recited inname only, then the application is prop-erly classified elsewhere outside thisclass.

SEE OR SEARCH THIS CLASS, SUB-CLASS:4, for maser-type amplifying device

which may involve a semiconductor.


1April 2009

5, for solid element wave propagatingamplifying devices involving cou-pling or activation by electromagneticwave energy applied through waveenergy constraining wave propagatingmeans, such as by wave guide.

307, for a claimed preferred embodimentof a patent application includes detailsof means to apply a variable electricalsignal to an IC amplifying device, ordetails of means to utilize the outputof an IC amplifying device.

SEE OR SEARCH CLASS:250, Radiant Energy, particularly sub-

classes 370.01+ for methods andapparatus using an invisible radiantenergy-responsive semiconductordevice.

257, Active Solid-State Devices (e.g.,Transistors, Solid-State Diodes),appropriate subclasses for activesolid-state devices, especially sub-class 115 which is directed to lightresponsive devices involving amplifi-cation. See (2) Note above.

313, Electric Lamp and Discharge Devices, appropriate subclasses for dischargedevices involving the structure of rayenergy generating, beaming andfocusing, in the form of electronbeams, alpha ray, and X-ray emana-tions.

315, Electric Lamp and DischargeDevices: Systems, subclasses 1+ forcathode ray discharge devices involv-ing circuits or special circuit structureassociated with the device.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, subclasses 509+ for miscellaneousnonlinear solid-state circuits subjectedto some external effect.


309 Involving structure of three diverse functionelectrode type:This subclass is indented under subclass 250.Subject matter wherein the semiconductordevice is provided in three diverse-type elec-trodes for coupling the signal energy input andoutput, additional biasing or gain control, etc..,and the application of the controlled electrical

energy source in which each electrode per-forms a distinct function.

(1) Note. If a claimed preferred embodi-ment of a patent application includesdetails of means to apply a variable elec-trical signal to an IC amplifying device,or details of means to utilize the outputof an IC amplifying device, that applica-tion is properly classified elsewhere inthis class.

(2) Note. If, however, a claimed preferredembodiment of a patent application islimited to details of an IC amplifyingdevice without details of the input oroutput (utilization) means, or the input oroutput (utilization) means are recited inname only, then the application is prop-erly classified elsewhere outside thisclass.


Transistors, Solid-State Diodes),appropriate subclasses for activesolid-state devices, especially sub-classes 115, 123 and 162 through 166which are directed to devices involv-ing amplification.

327, Miscellaneous Active Electrical Non-linear Devices, Circuits, and Systems, appropriate subclasses for similarsemiconductor devices in miscella-neous circuits.

310 Including plural stages cascaded:This subclass is indented under subclass 250.Subject matter including a plurality of stages ofamplification, such that the input signal foreach stage, except the first, is the output of thepreceding stage.

SEE OR SEARCH THIS CLASS, SUB-CLASS:3, for plural diverse-type amplifying

devices which may be cascaded andwhich may include a semiconductor-type amplifying device.

70+, for series energized vacuum tubeamplifiers which may be cascaded.

88+, 92 and 98+, for cascaded amplifierswith signal feedback.


April 2009

150, for cascaded vacuum tube amplifyingdevices of different characteristics.

151, for cascaded vacuum tube amplifierdevices with means to bypass a stage.

152+, for cascaded vacuum tube amplifiermeans differently coupled betweenstages.

157+, for interstage coupling between stagesof amplifying devices.

311 Having different configurations:This subclass is indented under subclass 310.Subject matter wherein at least one of the cas-caded stages is of a different configurationfrom at least one of the other cascaded stages.

(1) Note. In a semiconductor amplifier hav-ing emitter, base, and collector elec-trodes, input signal current flowsthrough two electrodes thereof, and out-put signal current flows through twoelectrodes thereof, one of the electrodesbeing common to both input and outputcircuits. Therefore, in the three elec-trode semiconductor amplifier, there is acommon electrode, an input electrodeand an output electrode. By the configu-ration of a semi-conductor amplifier ismeant the arrangement of base, emitter,and collector electrodes thereof, as theinput, common, and output electrodesthereof. The configuration is usuallyreferred to as common base, commonemitter, or common collector configura-tion, but this does not completely definethe configuration which must have atleast one of the other semiconductorelectrodes identified by its function asinput or output electrode.

SEE OR SEARCH THIS CLASS, SUB-CLASS:153, for cascaded vacuum tube amplifier

devices with differently coupled inter-stage circuits including at least onecathode follower stage.

157+, appropriate subclasses thereunder, forinterstage coupling to or from elec-trodes and as cathode, or from elec-trodes such as cathode or screen gridnot used in the majority of vacuumtube amplifiers as input or outputelectrode.

168, for vacuum tube interstage trans-former coupling from the cathode.

END

CLASS 330, AMPLIFIERS SECTION I - CLASS DEFINITION … · April 2009 CLASSIFICATION DEFINITIONS 330 - 1 April 2009 CLASS 330, AMPLIFIERS SECTION I - CLASS DEFINITION (A) This is the

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