OFFICIAL RADIO SERVICE MANUAL Supplement No. 2 242A GENERAL ELECTRIC CO. General Electric Modern Longfellow Grandfather Clock -Radio Models H-91 and H -91-R SERVICE NOTES ELECTRICAL SPECIFICATIONS Voltage Rating 105-125 Volts Frequency Rating 50-60 Cycles or 25-40 Cycles Power Consumption 120 Watts Recommended Antenna Length 25-75 Feet Type of Circuit A C. Screen Grid Super -Heterodyne Number of Radiotrons 3 RCA -235, 1 UY-224, 3 UY-227, 2 RCA -247, 1 UX-280.---Total of 10 Number of Radio Frequency Stages One Type of First Detector Tuned Input Grid Bias Number of Intermediate Stages Two Type of Second Detector Power Grid Bias Type of Automatic Volume Control UY-227 (Controlling bias voltage on R. F. and I. F. stages by means of drop across resistor in plate circuit) Number of Audio Stages One (Push -Pull) Type of Rectifier Full Wave, UX-280 Type of Loudspeaker Dynamic with Special High Frequency Filter Wattage Dissipation in Loudspeaker Field Ten Undistorted Output Four Watts PHYSICAL SPECIFICATIONS Height 78 Inches Depth 14,14 Inches Width 1712 Inches Weight (Packed for Shipment) 205 Pounds Weight (Alone) 136 Pounds Packing Case Dimensions 8112 Inches x 21Y4 Inches x 19 Inches INTRODUCTION General Electric Radio, Models H-91 and H -91-R are ten tube, Super -Heterodyne type radio receivers incorporated in the cabinet of a massive electric Grandfather dock. Mechanical and electrical excellence together with the beauty of fine period furniture characterize this instru- ment. Model II -91 is a straight radio receiver and model H -91-R is of the remote control type. Ten Radiotrons are used, three RCA -235 as R. F., and I. F. stages one UY-224 as first detector, three UY-227 as oscillator, automatic volume control and 2nd detector; two RCA -247 as the power out- put stage and one UX-280 as the rectifier. These instruments, with the exception of the cabinet are similar to the model H-51 and H -51-R except than an automatic volume control tube and Radiotrons RCA -235 and RCA -247 in the R. F., I. F. and Power stages, have been included. For service data other than on the remote control unit that is applicable to vertical operation and on the automatic volume control circuit, reference should be made to the Service Notes already issued on the Model H-51 and H -51-R.
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OFFICIAL RADIO SERVICE MANUALSupplement No. 2 242A
GENERAL ELECTRIC CO.
General Electric Modern LongfellowGrandfather Clock -Radio
Models H-91 and H -91-R
SERVICE NOTES
ELECTRICAL SPECIFICATIONSVoltage Rating 105-125 VoltsFrequency Rating 50-60 Cycles or 25-40 CyclesPower Consumption 120 WattsRecommended Antenna Length 25-75 FeetType of Circuit A C. Screen Grid Super -HeterodyneNumber of Radiotrons 3 RCA -235, 1 UY-224, 3 UY-227, 2 RCA -247, 1 UX-280.---Total of 10Number of Radio Frequency Stages OneType of First Detector Tuned Input Grid BiasNumber of Intermediate Stages TwoType of Second Detector Power Grid BiasType of Automatic Volume Control UY-227(Controlling bias voltage on R. F. and I. F. stages by means of drop across resistor in plate circuit)Number of Audio Stages One (Push -Pull)Type of Rectifier Full Wave, UX-280Type of Loudspeaker Dynamic with Special High Frequency FilterWattage Dissipation in Loudspeaker Field TenUndistorted Output Four Watts
PHYSICAL SPECIFICATIONSHeight 78 InchesDepth 14,14 InchesWidth 1712 InchesWeight (Packed for Shipment) 205 PoundsWeight (Alone) 136 PoundsPacking Case Dimensions 8112 Inches x 21Y4 Inches x 19 Inches
INTRODUCTIONGeneral Electric Radio, Models H-91 and H -91-R are ten tube, Super -Heterodyne type
radio receivers incorporated in the cabinet of a massive electric Grandfather dock. Mechanicaland electrical excellence together with the beauty of fine period furniture characterize this instru-ment.
Model II -91 is a straight radio receiver and model H -91-R is of the remote control type. TenRadiotrons are used, three RCA -235 as R. F., and I. F. stages one UY-224 as first detector, threeUY-227 as oscillator, automatic volume control and 2nd detector; two RCA -247 as the power out-put stage and one UX-280 as the rectifier.
These instruments, with the exception of the cabinet are similar to the model H-51 and H -51-Rexcept than an automatic volume control tube and Radiotrons RCA -235 and RCA -247 in the R. F.,I. F. and Power stages, have been included. For service data other than on the remote control unitthat is applicable to vertical operation and on the automatic volume control circuit, referenceshould be made to the Service Notes already issued on the Model H-51 and H -51-R.
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242H OFFICIAL RADIO SERVICE MANUAL
GENERAL ELECTRIC CO.
ISLACK
SYNCHRONOUSCLOCK
EN --
P
HOA .26A--RED
IFILAMENT
TRANSFORMER
BLACK -WITH -RED -TRACERLACK -WITH -RED -TRACER A.C.INPUT PLUG
Voltage readings were made with a 1000 ohm per volt meter. 250 volt
.The reeding here on a set analyser will show about 2 volts due tothe fact that the 2 meg. ohm resistor Is in series with the meter. To cheek gridvoltage, drop sore.e speaker divided by 2 will be the Approximate voltage appliedto grid. If plate cu oat ix about 25 mils and voltage *bout 220, it is safe toer.mie that the grid bias is O.K.
...Detector hie. reeding is taken at the overload point or an inoonlngsignal *more it generally reaches a maxima of 6 volts. With sere volume control,the reading here i. apiroximately 4 volts. This, of course. is not the true reed-ing, because resistance of volt meter becomes a parallel etreult, cutting down theresistance, and of ccuree. dropping the voltage. Reading taken in thie case waswith 10.000 ohm meter (1000 per volt. 10 volt aoale.)
...This reading is 'Object to considerable variation with metere ofvarious resistances. es the voltage at this point is measured through a 500,000 ohmresistor. The voltage at the opposite end of the resistor should be 220 volts.
TRANSFORMER VOLTAGES:
224 . 245 Filament on one eluding, 2.20 volts.280 Filament - 4.5High vo,tego minding. 315 each side of center tap.
RESISTANCE COLON CODE - CARBON RESISTORS.
1 Watt
10.000 ohms Brown with Slack bend, Orange Dot.30,000 - Orango with Black Bawd
500,000 " - Green with Bleak Band A Isilew Dot2 meg. - Bluu
2 Watt.
5,000 ohms - Green with Black Band and Fled Dot300 - P.P. Bias Resistor is wire wound.
RIXDITANCS, COIDR OHS - CARBON 113SISTORS.
3001100220030005000
100002000030000
1
1
2
100050000
1 WATT
Ohm - Wire Wound
" - Blue- Solid Red
Orange Black End-
- BrownRed
- Orange -meg - Red - Green
- Green Black- Brown- Purple- Brown -
- Green
ti
tt
It
It
ohmtt
it
If
Black
2 WATT
tl
If
11
- Red DotII at
- Orange DotIt
at
- Yellow
Green
at
fl
- Red- Orange "
5000 Ohm - Green with Black Band and Red Dot2200 " - Red300 " - R.F. Bias Resistor is Viire Wound.
RADIO FREQUENCY cgns.
Radio frequency coils in this Receiver arewound with 130, and 132 turns on the secondaries.The antenna coil has 132 turns, the second, thirdand detector coils have 130 turns.
0111
1111
1111
1
pS
WIT
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Aw
r
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P. I
7E7
300.
n.
7-7
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MO
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With the volume control at maximum, the following readings should be
obtained, with an allowable variation of 10i: -
R. F. Plate Voltage
1F)0
R. F. Screen Grid Voltage,
.75
R.
F. Grid Bias
2.5
R.
F. Plate Current,
2.5 M
First A.
F. Plate Current,
..
3}
M
First A.
F. Plate Voltage,
..
115
V
First A.
F. Bias,
5V
'45s Plate Voltage
225
V
'45s Bias,
50
V
'45s Plate Current,
30
M
Detector Screen Grid Voltage
50
V
Detector Bias
5V
Detector Plate Current,
2 M (No signal in Receiver)
Detector Plate Voltage,
100
4 or
,.
00
14
CO 0
OFFICIAL RADIO SERVICE MANUAL2 78E
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JACKSON -BELL CO., LTD.
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D.C. line 110 volts, voltages check as follows:-
R.F. Filament,
2 volts
R.F. Plate
90
"
R.F. Screen Grid,
60
"
R.F. Bias,
211
Detector Filament,
211
Detector Plate,
9C
"
Detector Bias,
10i
II
First Audio Filament,
2II
First Audio Plate,
90
ft
First Audio Bias,
2II
Push -Pall Filament,
2
Push -Pull Plate,
95
A
Push -Pull Bias,
12i
If
CARBON RESISTOR COLOR CODE.
ak Ohm - Wire Wound
1200
"- Blue
2200
It- Solid Red
3000
"- Orange
Black End
Red Dot
5000
"- Green
IIII
tlII
10000
"- Brown
"if
Orange Dot
20000
ft
- Red
-n
if
n
30000
II- Orange
-n
n-
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i-7,6
- Red
- Green
"Yellow
IT
- Green
- Black
n-
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1"
- Brown
-11
II- Green
"
2"
- Purple
1000 ohm - Brown
- Black.
"- Red
n
50000
"- Green
-ft
"- Orange
"
NOTE:
For a snort time, the 20,000 ohm is
solid black.
/IN
N 1
1111
1110
1.71
1,11
1111
111A
111
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.
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LL
IO
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01
Trans ilator
Oscillator
Oscilldor
Oscillator
Detector
Detector
Detector
4545
With volume control at maximum the following readings should be obtained with an
allowance of 10S for variation:-
I.F. Transilator and R.IP
Filament voltage
2 V.
I.P. Transilator and R.F
Plate voltage
245 V.
1.F. Transilator and fi.F
Screen grid voltage
120 V.
I.F. and R.F
Grid bias
2 W.
Grid bias
B W.
Filament voltage
2 V.
Plate Voltage
1E5 V.
Grid bias
4 V.
Filament voltage
P V.
Plate voltage
232 V.
Grid bias
5 V.
Filament voltage
Ei V.
Plate voltage
250 V.
'46
rrid bias
50 V.
'80
Filament voltage
49 V.
'90
Milliampere drain
DO M. per plate or a
total drain of
60 Mills.
10,000 s.
e
10 1
1,0.
isP
.
JAC
KSO
N-
BE
LL
SUPE
RH
EtE
RO
OM
E -
/YO
DE
L. 7
.9J.
H.H
.
.000
s
Csk
Q12
.0fI
SSZ
A0
a.1
/L
.4
I
I.F
= 1
75 K
c.
3ooc
f1.
7...0
0
44
27 5C .
With volumo control at maximum the following ruadinge should Do obtainod ml.th an
allowanco of 10% for voritions:-
I.F. Traneilutor and R.F
Filament Voltogo
2 V.
I.F. Transilator and R.F.... Plate Voltogo
245 V.
I.F. Traneilator and R.F.... Scroon Grid Voltogo
120 V.
Z.F. and R.F
Grid Bias
4 V.
Traneilator
Grid Bias
6 V
.Osoillator
Filamonb voltage
2 V.
Oscillator
Plato Voltogo
120 V.
Oscillator
Grid Bins
4 V.
Dotootor
Filamont Voltogo
2 V.
Dotootor
Plate Voltogo
255 V.
Dotootor
Grid Bias
6 V.
447
Filemont voltago
2/ V
..47
Plato voltage
250 V.
.47
Grid bins
16 V.
47
Space grid
176 V.
t.
'BO
Filqmont volt
ag44
V.
O'6
0Milllampore drain
30 M. por pinto or a
Ototal drain of
60 Mills.
I .5
- i I
----
---,
r---
_0.
4(-
,1)0
of ,-"!
tg&
L-
c,-
13
1 0,
0 C
0 S
I.
11
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2.50
4-1
'
OX
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2.5
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OFFICIAL RADIO SERVICE MANUAL326A
IIMMMNIMer
PHILADELPHIA STORAGE BATTERY CO.
Models 70 and 70-A Receivers(Above Serial No. B-22,000)
Model 70 Receivers are for operation on 100-130 volt, 50-60 cycle AC linesModel 70A Receivers are for operation on 100-130 volt, 25-60 cycle AC lines
Table 1 -Tube Socket Readings Taken with A.C. Set Tester -AC Line -115 voltsTube
FthussawtVolts
PlateVolta
ControlGridVolta
ScreenGridVolts
CathodeVolta
PlateMilli -
amperesType Circuit
35 R. F. 2.25 250 5 70 6 4.324 OSC & let Det. 2.25 250 8 12 8 .535 1. F. 2.25 250 21) 7(1 0 1.72735
*These readings must lie taken from the underside of the chassis, using test prods and leads unless the set checker is specially equipped fur testingpentode tubes.
Table 2 -Power Transformer Voltages
Terminals A.C. Volts Circuit Color
1-2 105 to 125 Primary White3-5 2.5 Filament of 24 and 35's Black6-8 2.5 Filament of 47 Dark Green9-10 5. Filament of 80 Blue
11-13 700 Plates of 80 Yellow4 Cenier Tap of 3-5 Black, Yellow Tracer7 Center Tap of 6-8 Black, Green Tracer
12 Center Tap of 11-13 Yellow, Green Tracer
Table .-Condenser DataNos. on Fills. I and 2 Capacity (mid.) Container
.00011
.00041
.0007
.003
Blue and YellowYellow and OrangeWhite and YellowOrange and White
@ 00 .01 Black Bakelite.015 (Double) Black Bakelite
ii1 1-21 26)Terminals2 3 ll 850 Long Tubular3-4(11650f
14 -5 I 1060).5 1,000 Brown Black Red
QA .5 2,900 lied White Red@) .5 10,000 Brown Black Orange
25,000 Red Green Oranges+..5.55.
51,00070,000
GreenViolet
BrownBlack
OrangeOrange
5 99,000 White White Orange: .5 330,000 Red Yellow Yellow.5 490,M1 Yellow White Yellow()
CI 40. 5
.5
. 5
1,000,0002,000,0004,000,000
BrownRedYellow
BlackBlackBlack
GreenGreen(;reen
326BOFFICIAL RADIO SERVICE MANUAL
PHILADELPHIA STORAGE BATTERY CO_
RECTiFtut 5.ocKET
2
0
59
CD®54
SPEAKERSOCKET
I 1.7 A.E
SOCKET
0 "0 SOCKET
0 0 0 0 0 000
SOCKET
0E7.- OSCSOCKET
SOCKET
OFFICIAL RADIO SERVICE MANUAL326C
PHILADELPHIA STORAGE BATTERY CO.
Model 90(Serial Nos. B-32,001 to B-35,000 and Above B-53,100)
Model 90 receivers are for operation on 100 to 130 volt, 50-60 cycle AC lines. This receiver isa nine tube superheterodyne with push-pull pentode output. Automatic volume control,4 point tone control, super control screen grid tubes and combination first detector andoscillator tube are some of the additional features. The maximum power consumptionis 100 watts.
Table 1 -Tube Socket Readings Taken with A.C. Set Tester-k.C. Line 115 VoltsTube
FilamentVolts
PlataVolts
ControlGridVolta
ScreenGrid
VoltaCathode
VoltsPlateMilii-
AmperesType Circuit
3524352727274747SO
R.F.Det.-Osc.
I.F.Det. RectifierDet. Amplifier
1st AudioOutput{
Rectifier
2.52.52.52.52.52.52.52.55.0
225215235
5090
210210
225/plate
01210
. .
00
1010
384038
225225
6221010
1.1.
4.2.5
1.0
1.05.0
31.31.
Above readings taken with volume control at maximum and dial turned to low frequnecy end.
Table 2 -Power Transformer VoltagesTerminals
Figs. I and 2 A.C. Volta Circuit Color1-2 115 Primary White
4 Center Tap Heater Black, Yellow Tracer3-5 2.5 Heater Black6-8 2.5 Filament 47's Dark Green7 Center Tap Filament 47's Black, Green Tracer9-10 5.0 Filament 80 Light Blue11-13 665 Plates 80 Yellow12 Center Tap Plates 80 Yellow, Green Tracer
Noe. on Figs.I and 2
eOO0
Table 3 -Condenser Data
Capacity (Mid.)
.0001100041.0007.001.01015
.05
.09.09 dr 200 Ohms.15
2-.25, 2-.56.6.
Container
Blue and Golden YellowYellow and OrangeWhite and Golden YellowGreen and WhiteBlack BakeliteBlack BakeliteBlack BakeliteBlack BakeliteBlack BakeliteBlack BakeliteMetal IElectrolyticElectrolytic
Table 4 -Resistor Data
Noa. on Figs.I and 2 Power
(Watts) Resistance(Ohms)
Color
Body Tip Dot
(Terminals)1-2 2052-33-4
952,400 Long Tubular
4-5 1,2001. 1,000 Brown Black Red.5 10,000 Brown Black Orange.5 15,000 Brown Green Orange44)@ .5 25,000 Red Green Orange.5 51,000 Green Brown Orange.5 99,000 White White OrangeO .5 490,000 Yellow White Yellow.5 1,000,000 Brown Black Green
326DOFFICIAL RADIO SERVICE MANUAL
,1
PHILADELPHIA STORAGE BATTERY CO.
7; DET-o5c
PIIILCO MODEL 9 0
RECTIFIERSOCKET
68 1008048 , CI 0 0 0
SPEAKER DET,Am P.
SOCKET SOCKET SOCKET
DET.SOCKET
SPEAKER PLUG AMO SOCKITCOHNECTiONS SHOWN -MI 0-
I. F.
SOCKET
OFFICIAL RADIO SERVICE MANUAL326E
PHILADELPHIA STORAGE BATTERY CO.
Conoenser 3615 .05 Mfd.
PNarto.
Cond.Cap.Mfd.
LugsUs( d
WireReels.Ohms
WiringEnsis.-
-Alga
Cond.WiringLugs
3615-B .05 1-3-5 250 3-5 1-5
13615-C .05 1-5-7 250 5-7 1-5
3615-D .05 1-3-5 ... 1-5
1 3615-E .05 2-5 ... ...3615-F .05 2-3-5 ... 3-5
3615-G .05 5-8 ...- '
3615-H .05 3-5-8 '5-8
36154 .05 1-5-7 ...'
1-5
3615-K .05 3-5-8 250 3-5 5-8
3615-L .05 1-5 ...
3615-M .05 2-5-7 2-3
1-4
1-4
1-3
3615-N .05 1-4-7
3615-P .05 1-1-7 250 1-7
5-73615-R .05 1-5-7 2.10
3615-3 .05 1-4
3815-T .05 1-5-7 150 1-7 1-3
3615-U .05 1-5-7 1-7
3615-W .05 1-2-5
1-7
1-5
,1-:1
1-5
1-7
1-S
3615-X .05 1-2-5-7 150
3615-Y .05 1-2-5-7 1.10
3615 -AA .05 1-3-5-8
3615 -AB .05 1-4-7-8 1-1
3615 -AC .03 1-5-7-8 ... 1-7
3615 -AD .05 3-5-8 ... 3-3
3615 -AE .05 1-7-8 7-5
3615 -AF Twin .05 4-7-8 4-8 J: 7-8
3615 -AG .05 1-3-5 1-3
3615-AH .05 1-5 1-3
3615-AJ Twin .05 1-3-6-8 ... 1-3 & 1-6
3615 -AK .05 1-5-7-8 ... 1-7
Standard By -PassCondenser Data
The tables below list the various Philcostandard bypass condensers in blackbakelite containers. 'the drawing showsall possible lug arrangements and thetables list the lug numbers.
PHILADELPHIA STORAGE BATTERY CO.Checking I. F. Oscillator Calibration
Any oscillator which is not crystal controlled particularly those which are battery oper-ated and portable, should be checked from time to time for correct frequency calibration. Thecalibration can be appreciably affected by rough handling of the oscillator while it is beingmoved about, and by the condition of the tubes and batteries. If an oscillator is in constantdaily use, it should be checked two or three times a week and any necessary adjustment madeto correct errors in calibration.
One of the most accurate and convenient methods of making this check is through the useof the signals from reliable broadcasting stations. Most of the better class stations have accu-rate crystal controlled frequency regulation which assures broadcasting on the assigned fre-quency. Intermediate frequency oscillators can be checked with the aid of broadcast signalsin the following manner:
175 KC Intermediate Frequency Oscillator Check-Place radio set in operation, andtune it accurately to a station broadcasting on any of the following frequencies: 700, 1050, or1400 KC. When a station is heard at any one of these three points, disconnect the antennaand substitute a connection to the output of the oscillator. Place the oscillator in operation at175 KC. If the oscillator is calibrated correctly, its signal should be heard on the receiverwithout changing the tuning of the broadcast receiver in any way. If it is necessary to re -tunethe set before the oscillator signal can be heard at maximum volume for the particular settingof the attenuator and the radio set volume control, the oscillator is off calibration. Its compen-sating condenser should be re -adjusted until the signal is heard at exactly 700, 1050, and 1400KC. (These frequencies are the fourth, sixth, and eighth harmonics of 175 KC.) In the PhilcoOscillator Model 095, this compensating condenser is the one nearer the 175 KC switchposition.
260 KC Intermediate Frequency Oscillator Check-Proceed in the same manner a,for the 175 KC check described above, but tune the broadcast receiver to a signal at 780, 1040,or 1300 KC. Remove the antenna and substitute the connection from the oscillator, thelatter being in operation at 260 KC. Check in the same manner as for 1'75 KC, making anynecessary adjustments of the 260 KC compensating condenser so as to make the oscillatorsignal heard at 780, 1040, or 1300 KC. (Third, fourth, and fifth harmonics, respectively of260 KC). In the Philco 095 oscillator, this compensating condenser is nearer the 260 KCswitch position.
POWER CONSUMPTION OF PHILCO MODELS
A number of requests have been received for information on thepower consumption of various Philco Receivers. The table below lists thedifferent instruments with the power consumption in watts of each.
Model Watts
511 75 A . C .
65 95 11
86 9087 9576 9577 9595 10596 105 "
296 14520 75 "
220 100 "
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The power consump- 90 95
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models is the sane 212 135as that of the 60 270 100 "
cycle models. Instru- 40 210 D.C.ments rated at 230volts consume thesame power as thoserated at 110 volts.
Victor Radio R-12Victor Console, R-12 is a nine tube
Super -Heterodyne Radio Receiver pro-viding excellent performance in all thefeatures incorporated in modern radiobroadcast receivers.
Automatic volume control, push-pullPentode output stage, tone control,calibrated kilocycle dial, acousticallycorrect cabinets and the inherentsensitivity, selectivity and tone qualityof the Super -Heterodyne are some ofthe features of this receiver. Referringto Figure I, the schematic circuit dia-gram, and tracing a signal through thevarious stages, we find the followingaction taking place.
The first tube is the tuned R. F.stage. This is the new Super ControlScreen Grid Radiotron, UY-235. Theoutstanding feature of this Radiotronis that due to its grid potential platecurrent curve having a constant rateof curvature, cross modulation, modu-ation distortion, and hum modulationeffects are eliminated from the receiver.Also it is very adaptable to automaticvolume control action due to itscharacteristics that preclude the neces-sity of a local distant sw:tch. Thecontrol grid bias for this Radiotron isvaried by means of the automaticvolume control tube.
The output of this circuit is coupledinductively to the grid coil of the firstdetector. At this point the oscillatorshould be considered as its output isalso coupled inductively to the gridcoil of the first detector. This is atuned grid circuit oscillator using aRadiotron UY-227, and having aclosely coupled plate coil that givessufficient feed -back to provide stableoperation. The grid circuit is sodesigned that by means of a correctcombination of capacity and induct-ance a constant frequency differencebetween the oscillator and the tunedR. F. circuits throughout the tuningrange of the receiver is obtained.
The next circuit to examine is thefirst detector. The circuit is tuned bymeans of one of the gang condensers tothe frequency of the incoming signal.Radiotron UY-224 is used in this stage.In the grid circuit there is present theincoming signal and the oscillatorsignal, the latter being at a 175 K. C.difference from the former. The firstdetector is biased so as to operate as aplate rectification detector and itspurpose is to extract the difference orbeat frequency, produced by combin-ing the signal and oscillator frequen-cies. The beat frequency ---175 K. C.- appears in the plate circuit of thefirst detector which is accurately tunedto 175 K. C.
The next stage is that of the I. F.amplifier. A single stage is used,requiring two I. F. transformers, con-sisting of four tuned circuits. Theplate circuit of the first detector, thegrid and plate circuit of the I. F.amplifier and the grid circuit of thesecond detector are all tuned to 175K. C. Radiotron UY-235 is used inthis stage and its control grid voltageis also varied by means of the auto-matic volume control tube.
At this point it is well to considerthe action of the automatic volumecontrol tube as it controls the R. F.and I. F. amplifiers of the receiver.The automatic volume control func-tions in the usual manner in that thesignal voltage is applied to its grid andthe voltage drop across a resistor inthe plate circuit is the grid voltageapplied to the I. F. and R. F. stages.As the value of the plate current is adirect result of the signal voltageapplied to the grid, a greater platecurrent gives a greater voltage dropacross the resistor in its plate circuitand therefore a higher bias on the I. F.and R. F. stage. This results in lesssensitivity and vice versa. The signaloutput of the I. F. stage is alwaysmaintained at a constant value.
The volume control should now beconsidered as its position in the circuithas a large bearing on the quiet andsmooth action of this receiver.
In previous automatic volume con-trol receivers, the volume control wasplaced in the grid circuit of the auto-matic volume control tube, its actionbeing to vary the control grid voltageof this tube. When operating sets ofthis character, the receiver jumped tofull sensitivity when not tuned to asignal and if in a noisy location, thisnoise was very objectionable.
In this instrument, however, thevolume control is not in the automaticvolume control tube circuit, but in thegrid circuit of the second detector. Bymeans of it the signal voltage appliedto the second detector is controlled andunder no conditions can noise or othersignals exceed the level for which it hasbeen set. Electrically, the primary andsecondary of the second I. F. trans-former are shielded from each otherso that there is no transference ofenergy except by means of a smallpickup coil. The volume control is apotentiometer shunted across this coilwhich determines the amount of pickupthat will be used. As a further meansof controlling a strong signal, a secondsection is provided which places up to10,000 ohms (R-21) in series with thetuned circuit of second detector grid.This effectively reduces even themost powerful signals received.
The second detector is a high -platevoltage, grid -biased type, using Radio-tron UY-227, which gives sufficientoutput to drive two Radiotrons UY-247 connected in push-pull without anintermediate audio stage. The purposeof the second detector is to extract theaudio frequency component of theR. F. signal which represents the voiceor musical modulations produced in thestudio of the broadcasting station. Theaudio component is extracted and usedto drive the power tubes while theR. F. current is by-passed and notfurther used.
A grid filter consisting of a 1 meg-ohm resistor (R-13) in the seconddetector circuit and a 0.5 megohmresistor (R-4) in the R.F. circuit helpsto reduce any possible hum in thesestages. The power A. F. stage consists
of two Radiotrons UY-247 connectedin push-pull. Transformer coupling isused between the detector and thegrids of the Radiotrons UY-247 aswell as from the plates to the cone coilof the reproducer unit.
A tone control, consisting of a 0.008mfd. condenser in series with a 200,000ohm variable resistor connected acrossthe two grids of Radiotrons UY-247is incorporated in this stage. The tonecontrol functions to reduce the highfrequency output as the resistance isreduced. At the extreme low position,the condenser and secondary of theA. F. transformer resonate at a lowfrequency and thereby further ac-centuate the bass response. The two0.0004 mfd. condensers, connected inseries with their mid -point groundedare connected across the secondary ofthe input transformer. The purpose ofthese condensers is to prevent audiooscillations and provide a high fre-quency audio cut-off.
A 0.005 mfd. condenser connectedin series with a 10,000 ohm resistor isplacid across the primary of the outputtransformer. This functions to reducethe third harmonic distortion, aninherent characteristic of the Pentodeoutput tube. The direct plate and gridvoltages are supplied from high volt-age alternating current which is recti-fied by means of Radiotron UX-280.The filter is of the tapped reactor typewhich gives an output of well filteredD. C. The bias voltage for the Radio-trons UY-247 is obtained by using .aportion of the drop across the repro-ducer field. One 190,000 ohm and one40,000 ohm resistors act as the voltagedividing resistors.
SERVICE DATAInformation pertaining to general
service data for this type receivermay be obtained from the ServiceNotes already issued on the VictorRadio Superette. Figure 1 showsthe schematic diagram, Figure 2 theproper connections for attaching amagnetic pickup to the R-12 and Fig-ure 3 the wiring diagram. The voltagereadings and replacement parts areshown on page 3.
R. F. OSCILLATOR ANDI. F. ADJUSTMENTS
A reference to the Victor RadioSuperette Service Notes will givethe details for making correct R. F.,I. F. and Oscillator adjustments. How-ever, due to the use of an automaticvolume control tube, its action will de-feat the use of an output meter. Toovercome this, a "dummy" RadiotronUY-227 (one that has one heater prongremoved but is otherwise O.K.) shouldbe substituted for the tube in the auto-matic volume control socket. Do notmake any adjustments with thistube removed from the socket.While apparently everything functionsin the normal manner, the lack of tubecapacity in the circuits will cause anincorrect alignment to be made.
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326LOFFICIAL RADIO SERVICE MANUAL
RCA -VICTOR, INC.
SUPPLEMENT
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VICTOR RADIO R-12 SERVICE NOTES
Late production of the Victor Radio R-12 has a slight changein the wiring, two changes in capacitor values and the addition of a 0.5megohm resistor (R-20). Capacitor C-7 has been changed from 0.5 mfd.to 0.1 mfd. and C-13 from 0.1 mfd. to 0.05 mfd. Resistor R-20 has beenadded.
Figure 1 shows the revised schematic diagram and Figure 2 thewiring diagram.
The replacement parts listed and supplied are entirely interchange-able with either the old or new models. In the case of the older models,however, the additional black lead supplied in the new capacitor packshould be joined to the old black ground lead. All other capacitor leadsare exactly the same and are soldered to the same points.
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OFFICIAL RADIO SERVICE MANUAL326N
RCA -VICTOR, INC.
SERVICE NOTESfor
VICTOR RADIO R-20 and R-21The Victor Radio R-20 and R-21
are ten tube screen grid automaticvolume control Super -Heterodyne radioreceivers. With the exception of theAudio Transformer, Speaker and Cabi-net both models are identical.
Features of these Models are. SuperControl Screen Grid Radiotrons in theR. F. and I. F. stages, automaticvolume control so arranged in thecircuit to reduce noise between chan-nels, push pull Pentode output stage,accurately calibrated dial readingdirectly in kilocycles, totally shieldedchassis and sensitivity, setactiVity andfidelity superior to any previousVictor receiver.
Referring to Figure 1 and tracing asignal through the various stages, wefind the following action taking place.
The signal voltage, indsuced into theantenna system, is coupled by meansof the antenna coil to the tuned circuitof the "link circent." The link circuittunes exactly with the tuned R. F. andfirst detector circuits. There is nogain in the circuit, it being merely aselection circuit.
A tuned R. F. stage follows whichuses Radiotron UY-235. The controlgrid bias for this tube is a function ofthe automatic volume control tube. Theoutput is coupled inductively to thefirst detector grid circuit together withthe output from the oscillator.
The first detector is tuned by oneunit of the gang condenser. In itsgrid circuit, there is present the incoming signal and the oscillator signal, thelatter being at a 175 K. C. higherthan the former. The tube is biasedso as to operate as a plate rectificationdetector and its purpose is to extractthe difference or beat frequency, produced by combining the signal andoscillator frequencies. The beat fre-quency -175 K. C. - appears in theplate circuit of the first detector whichis accurately tuned to 175 K. C. Thetube used as a first detector is Radio-tron UY-224.
The next circuit is that of the firstI. F. stage. It is a high gain Amplifierhaving both its grid and plate circuitstuned to 175 K. C. Its grid voltage iscontrolled by the automatic volumecontrol tube.
At this point the automatic volumecontrol tube should be considered asits grid is controlled by the output fromthe first I. F. Stage.
The automatic volume control tubez-nunncr in that
the signal voltage is applied to its gridand the voltage drop across a resistor
in its plate circuit is the grid voltageapplied to the R. F. and first I. F.amplifier. As the value of the platecurrent is a direct result of the signalvoltage applied to the grid, a greaterplate current gives a greater voltagedrop across the resistor in its platecircuit and therefore a higher bias onthe R. F. and I. F. stage. This resultsin less sensitivity and vice versa. Thesignal output of the first I. F. stage isalways maintained at a constant value.
The volume control should now beconsidered as its position in the circuithas a large bearing on the quiet andsmooth action of the receiver.
In previous automatic volume con-trol receivers, the volume control wasplaced in the grid circuit of the auto-matic volume control tube, its actionbeing to vary the control grid voltageof this tube. When operating sets ofthis character, the receiver jumped tofull sensitivity when not tuned to asignal and if in a noisy location, thisnoise was very objectionable.
In this instrument, however, thevolume control is not in the automaticvolume control tube circuit, but in thegrid circuit of the second I. F. Amplifier.By means of it the signal voltageapplied to the second I. F. amplifier iscontrolled and under no conditions cannoise or other signals exceed the levelfor which it has been set. Electrically,the primary and secondary of thesecond I. F. transformer are placed sothat there is no transference of energyexcept by means of a small pickup coil.The volume control is a potentiometershunted across this coil which deter-mines the amount of pickup that willbe used.
The second detector is a high -platevoltage, grid -biased type, using Radio-tron UY-227, which gives sufficient out-put to drive two Radiotrons UY-247connected in push-pull without anintermediate audio stage. The purposeof the second detector is to extract theaudio frequency component of theR. F. signal which represents the voiceor musical modulations produced inthe studio of the broadcasting station.The audio component is extracted andused to drive the power tubes whilethe R. F. current is by-passed and notfurther used.
A grid filter consisting of a 1 megohmresistor in the second detector circuithelps to reduce any possible hum inthese stages. The power A. F. Stageconsists of two Radiotrons UY-247connected in push-pull. Transformercoupling is used between the detectoranti tin: grids of tlic Radiutran UY-247as well as from the plates to the conecoil of the reproducer unit.
A tone control, consisting of aninductor .01 mfd. Capacitor and a 0.5meg. variable resistor is in the platecircuit of the second detector. Thetone control functions to reduce thehigh frequency output as the resistanceis reduced, without accentuating thebass response. The two 0.0004 mfd.condensers, connected in series withtheir mid -point grounded are connectedacross the secondary of the imput trans-former. The purpose of these con-densers is to prevent audio oscillationsand provide a high frequency audiocut-off.
A 0.005 mfd. condenser connected inseries with an 18,000 ohm resistor isplaced across the primary of the outputtransformer. This functions to reducethe third harmonic distortion aninherent characteristic of the Pentodeoutput tube. The direct plate andgrid voltages are supplied from highvoltage alternating current which isrectified by means of Radiotron UX-280. The filter is of the tapped reactortype which giilles an output of wellfiltered D. C. The bias voltage ofRadiotrons UY-247 is obtained byusing a portion of the drop across thereproducer field. One 100,000 and20,000 ohm resistors act as the voltagedividing resistors.
SERVICE DATA
Information pertaining to R. F.,oscillator and I. F. adjustmentstogether with general service data forthis type receiver may be obtainedfrom the Service Notes already issued.Figure 1 shows the schematic diagram.
R. F. OSCILLATOR ANDI. F. ADJUSTMENTS
A reference to the Victor RadioSuperette Service Notes will give thedetails for making correct R. F., I. F.and Oscillator adjustments. However,due to the use of an automatic volumecontrol tube, its action will defeat theuse of an output meter. To overcomethis, a "dummy" Radiotron UY-227(one that has one heater prong removedbut is otherwise 0. K.) should be sub-stituted for the tube in the automaticvolume control socket. Do not makeany adjustments with this tube re-moved from the socket. While appa-rently everything functions in thenormal manner, the lack of tubecapacity in the circuits will cause anincorrect alignment to be made.
In the Model R-20 and R-21 theI. F. transformers are adjusted formaximum output and no attempt atband pass tuning should be made whenthese adjustments are made.
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OFFICIAL RADIO SERVICE MANUAL578D 51ftPlettrcitt No. e
AUTOMOBILERADIO
ANDSERVICINGA (molds Tnsmsa a tia Salaam
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S4 PAGES. Size, 6 x 9 InchesOver 65 Illustrations
Bound in stilt beard corers
-Announcing RADIO -CRAFTthePresented on these two pages are the new books of the
RADIO -CRAFT LIBRARY-the most complete and authenticset of volumes treating individually, important divisions ofradio. Each book has been designed to give radio men the
RADIO SET ANALYZERSAnd How To Use Thee
- With Full Instructions and Descriptions ofSet Analyzers. Tube Checkers,
On'Haters. Etc.
RADIO SETANALYZERS
AND
How to UseThemAL 54 . mai df elA .1
o'iL Va tior 55416ile
Price 50c
C4 PAGES. Size. 6 x 9 InchesOver 50 Illustrations
Bound in stilt board corers
By L. VAN DER MEL
This book explains thoroughly the oper-ation u: set analyzers, tube checkers,oscillators and other testing equipment.For every radio man, whether junior gradeor expert, this book is extremely helpful.It covers every phase of testing and givesyou valuable short cuts : completely illus-trated with photographs and diagrams tofacilitate the use of modern testingequipment.
The following chapters briefly outlinethe contents. INTRODUCTION: THEANALYZER: Fundamentals, Switches,A.C. and D.C. Voltmeters, Calibration andDesign : TROUBLE SHOOTING WITHTHE ANALYZER: Classification of Trou-ble, Analysis of Electrical Troubles. Fea-tures and Uses of Various Analyzers,Care and Maintenance; CONCLUSION:Summary.
HOW TO BECOME A RADIO SERVICE MANHow To Get Started and How To Make
Money In Radio Servicing
By LOUIS MARTIN
The ambition of many men in radiotoday is to become a first -grade ServiceMan, with a business that is flourishing.It is not as difficult as one might believe,but it cannot be done in a few shor.months. Following very carefully theadvise of Mr. Martin. who has dealtwith r4se problems of thousands of Ser-vice Men, this book deals very carefullywith the essential stages in the prepara-tion fur qualifying as a Service Man.The Chapters of the book are so dividedthat each element is thoroughly covered.
Here are the chapters: The Small In-dependent Service Man ; Advanced Com-mercial Aspects: The Radio Set ; Semi -Technical Considerations; Advanced Ser-vice Data. Each chapter is again sub-divided to bring out in minute detailevery point of importance.
usio-citAfTLIBRARyfre
HOWTO BECOMEA RADIOSERVICEMAN
Or or. Mr...
64 PAGES. Size, 6 x 9 InchesOver 55 Illustrations
Bound In stiff board covers
AUTOMOBILE RADIO AND SERVICINGA Complete Treatise on the Subject Cov-ering All Phases from Installing to Ser-
vicing and Maintenance
By LOUIS MARTIN
Automobile radio is ip and coming.and someone has to service them properly.It is certain that one of these days yourturn will come, whether you are an ex-perimenter or Service Man. It thereforebehooves you to read this immensely im-portant new book on the art of Auto-mobile Radio. There is no better bookin print and none as concise. The bookis full of illustrations, photographs, dia-grams and hookups.
Here are only a few of some of thereally interesting chapters: Introduction ;A:__omotive Radio Installations : CompleteDescriptions of Commercial AutomotiveReceivers : Servicing Automotive Receiv-ers : The Ignition System: General Ser-vice Considerations ; Effects of Tempera-ture on Power Supply : Conch: inn.
opportunity to specialize in one or more of the popular branchesof the industry. The material contained in these 1,,oks willincrease your knowledge; you will find them a real help inyour work and they will contribute to your money earning
ti
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MODERN VACUUM TUBESAnd Hew They Work
With Complete Technical Data on AllsopKIATTLIBBARyAr..2 FJ
MODERNVACUUM
TUBESAND
How They WorkwillItte do.
.11 stsoliard eves..S .petrol t
Sy RA.. Htti.loe,
84 PAGES. Size. 6 x 9 InchesOver 100 Illustrations
Bound in stiff beard corers
Standard and Many Special Tubes
By ROBERT HERTZBERG
MODERN VACUUM TUBES describesthe fundamental electron theory which isthe basis of all vacuum tube operation,and goes progressively from the simplesttwo -element tubes right up to the latestpentodes and thyratrons. It is writtenin clear, simple language and is devoidof the mathematics which is usually soconfusing. Valuable reference charts andcharacteristic curves of standard andspecial tubes are to be found, also dia-grams of sockets and pin connections.
Here are some of the chapters: Th,Edison Effect and The Electron TheoryElectron Emitters and the Ionization Ef-fect: The Three -Electrode Tube; VacuumTube Characteristics ; Four- and Five -Element Tubes: Light Sensitive Cella andOther Special Tubes.
BRINGING ELECTRIC SETSWith Pentodes, Multi - Mus, DynamicSpeakers-Complete Information How toModernize A.C., D.C. and battery Operated
Receivers
By CLIFFORD E. DENTONIn this country there are over ten mil-
lion electrically operated receivers thatcould be modernized-by placing in themnew type tubes, new speaker equipmentand other modern improvements. Thisbusiness of improving old sets can go tothe experimenters and Service Men ifthey will quickly jump into action.
Read in this book by Mr. Denton, howeasily you can modernize any obsolete set.Your clients can retain their expensivecabinets and still have a receiver that isright -up-to-the-minute, and with littleadditional co s.
Here are t.,e high lights of this book:Tubes Available for Replacements ; Elec-trifying Battery Receivers Use of theNew 2- and 6 -Volt Tubes: Operating Setswith Single Control ; Conversion of A.C.Sets into D.C.. and D.C. into A.C.: Re-placing Output Tubes with Higher OutputTubes; Improving Old Supers: Loftin -White Amplifiers ; Adapters and Their Use.
HOME
UP TO DATE
64 PAGES. Size. 6 x 9 InchesOver 80 Illustrations
Bound in stiff board corers
RECORDING AND ALL ABOUT IT
HOMERECORDING
D
ALL ABOUT ITA Complo Tv* soih
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64 PAGES. Size, 6 x 9 InchesOver 70 Illustrations
Bound in 4444f beard corers
A Complete Treatise on InstantaneousRecording Microphones, Recorders, Ampli-fiers, Commercial Machines. Servicing, etc.
By GEORGE J. SALIBA
If there is one subject that is fascinat-ing to every radio man, it is that of HomeRecording. Of course, this volume isnot all on "Home" recording, but theinformation contained therein is impor-tant to commercial radio men, studiooperators, engineers and others interestedin this phase of radio.
The art of recording and reproducingbroadcast selections is becoming more im-portant every day to radio men, experi-menters and Service Men. Equippingdance halls, auditoriums, churches, res-taurants and homes with public addressand amplifiers brings many extra dollarsand often an excellent income.
In this book are found such topics as:Short History of the Art; Microphones ;Recording Amplifiers ; Cutting Heads:Types of Records ; Commercial Machines:Adding Recorders to Receivers ; StudioLayouts ; Mechanical Filters for Turn-tables.
OFFICIAL RADIO SERVICE MANUALSup filebtent No. 2 578E
LIBRARYcapacity. Read these books during your spare time at home.
The authors of these books are well-known to everybody.Each one is an expert radio man; an authority on the subject-each is thoroughly familiar with the field which he represents.
THE SUPERHETERODYNE BOOKAll About Superheterodynes
How They Work,' How to Build and Howto Service Them
By CLYDE FITCH
There is no more fascinating a subjectin the large array of radio circuits thanthe famous superheterodyne circuit. Ithas taken the world by storm, and todaypractically all modern receivers employthis principle of design. Whether youare a Service Man or experimenter, first-hand kno,. ,o,g5. about the construction ofthese receivers is very important. Thebook on Superheterodynes gives underly-ing principles of their construction, rightfrom the very first set made. Masteringthe fundamentals of this circuit will en-able you to build or service any receiver.
The following is a short list of con-tents: Basic Principles of the Superheter-odyne; The Oscillator ; First Detector ;Single Dial Tuning Systems; Interme-diate Amplifier; Second Detector, AudioAmplifier and Power Supply; CommercialSuperheterodyne Receivers; ServicingSuperheterodynes.
64 PAGES. Size, 6 x 9 InchesOver 60 Illustrations
Bound in stiff board covers
RADIO KINKS AND WRINKLESFor Service Men and Experimenters
A Complete Compen'um on the LatestRadio Short -Cuts and Money -Savers
By C. W. PALMER
It often becomes necessary for experi-menters and Service Men to call upontheir memory .ar some short cut or radiowrinkle that will solve a problem quickly.In busine "short cuts" mean time andmoney saved, and to the Service Man"time saved" means money earned,
This book is a compilation of importantradio kinks and wrinkles; the entirecontents of the book has been selectedwith great care in order to discuss onlysuch items as are constantly used today.
Here are some of the more importantchapters: Introduction : Servicing Short -Cuts ; Testing Equipment and Meters;Vacuum Tubes and Circuits; Volume -control Methods; Amplifiers and Phono-graph Reproducers; Power Supply Equip-ment Coils and Tuning Circuits; ShortWaves; Loud Speakers; Tools and Ac-cessories.
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RADIOKINKS
WRINKLESFor Service Men and
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Over 78 IllustrationsBound in stiff board covers
This is perhaps the first real opportunity that you have everhad to build a radio library of books that are authentic, right -up -to -the -minute and written so that it is easily digested andclearly understood. Mail the coupon below for your books.
MODERN RADIO HOOK-UPSThe Best Radio Circuits
A Complete Compendium of the Most Im-portant Experimental and Custom-
built ReceiversBy R. D. WASHBURNE
It is fascinating to the experimenter,or even to the up-to-date Service Man,to take a commercial set and to changeit into one using a famous hookup thatis nut found in any manufactured set;and it is usually worth the trouble be-cause results are far superior than in theoriginal. Many excellent circuits havenever been commercialized, but limitedonly to home -set builders. Thousands ofthese popular circuits have been requestedfrom time to time, and in this book wehave included over 150 circuits, whichinclude the famous Peridyne, Cash -BoxA.C.-D.C. Set, and others.
The circuits cover the following:BROADCAST RECEIVERS ALL -WAVERECEIVERS, SHORT-WAVE RECEIV-ERS, CONVERTERS AND ADAPTERS,TELEVISION RECEIVERS. HOME RE-CORDING APPARATUS. AUTOMOBILERECEIVERS. AUDIO ANn POWER AM-PLIFIERS, POWER UNITS and MIS-CELLANEOUS EQUIPMENT.
se
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MODERNRADIO
HOOK-UPS.The Best Rack Circuits
A Cam. -L.. J 6.1
fyAAA.1
64 PAGES. Size. 6 x 9 InchesOver 120 Illustrations
Bound in stiff board covers
RADIO QUESTIONS AND ANSWERSA Selection of the Most Important of 5.000Questions Submitted by Radio Men During
the Course of One YearBy R. D. WASHBURNE
There has been collected a wide varietyof questions which have come into oureditorial offices during the past two years,and only those whose answers wouldbenefit the majority of men engaged inradio have been incorporated in thisamazing question and answer book.
The tremendously long list of topicsbetter explains the subjects which arc.treated. Here are the titles:
Radio Servicing: Receiver Design ; The-ory ; Home Recording: Television : SoundEquipment: Short Waves; Antennas:Operating Notes: Test Equipment ; Vaer-uum Tubes: Engineering; Ultra -Short -Waves Police Radio: Reproducer,::Graphs: Superheterodynes; AutomotiveSets; Power Packs; Automatic VolumeControls; Remote Control Devices; Align-ing Procedure; Photoelectricity ; ToneControl ; Coil Construction ; Adapters :Measuring Apparatus: Band -Selectors;Meters : Symbols: Microphones : Conver-ters: Definitions ; Public Address Equip-ment; Modernizing Methods: Set Analy-zers; Midget Sets ; Oscillators: Phono-graph Pickups; Tube Testers; Diagrams.
-!, r"sogo-CSAFTEIBRAStse8
RADIOQUESTIONS
ANSWERSA &4A. a/ As M, /Apo,. wi LOCO 0.9.
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64 PAGES. Size, 6 x 9 Inches0,er 80 Illustrations
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OFFICIAL RADIO SERVICE MANUAL578F
SUPPLEMENT No. 2
Index and Incidental Information
THE index below lists all the dia.grams contained in both the first and
second supplements to the 1932 OFFICIAL.RANO SERVICE. \IANUAL. Flace this sheetbefore page 579, so that it will he asclose as possible to the main index. Inlooking for a particular receiver, he sure
GENERAL ELECTRIC CO.Models H-91 and H-91 -R (LongfellowGrandfather Clock)
242A to 2421
GENERAL MOTORSRADIO CORP.
Model 211 176EMcdel 220 176GModel 281 Converter 242J
to consult both this index and the mainindex.
The completely revised index prom-ised with this supplement could not becompleted in ime because of the greatamount of work involved in its prepara-tion, but it will definitely be included
JJACKSON -BELL, Ltd
Model S 278AModel 8 278BModel 50 278CModel 68 278DModel 69DC .278E, 278FModel '79 278GModel 89 278HModel 645M 2781Model 845S 278J
Owners of the OFFICIAL RADIO SERV-ICE NIANUAL are requested to observe a.few simple rules in regard to the ques-tion service. First of all, please bear inmind the fact that it is necessarily limit-ed fo matters concerning commercial re-ceivers. Out of justice to the hundredsof Service Men who send in legitimateservice inquiries every week, we cannotundertake to do special design work,draw up elaborate diagrams to fit oddcollections of parts, enter into involveddiscussions of radio theory, identifymysterious short-wave stations, or desimilar jobs that have no relation toservice work.
Answering straight service letters is
enough of a problem in itself, as fre-quently this involves considerable dig-ging through files of service manuals.Sometimes fifteen or twenty minutes ofresearch is necessary merely for a yesor no answer to a question.
We cannot offer opinions on the rela-tive merits of different makes of appa-ratus, nor can we obtain discounts onany kind of merchandise. if you wantcatalogs or special data from a manu-facturer, write to him directly; if youdo not know his address, send your let-ter. in a stamped envelope, to us, andwe will forward it.
with the third supplement. It will ap-pear in a new and more convenientform, and will include every diagrampublished in both the 1931 and 193?MANUALS and in all the supplements.As a record of commercial receivers itwill he of great interest and value toall radio Service Men.
PHILADELPHIA STORAGEBATTERY CO.
Models 70 and 70A326A, 326E
Model 90 326C, 326DStandard By - PassCondenser Data ... . 326ERadio Chassis Data. .326FChecking' if Oscil-lator Calibration...326G
Please be reasonable arid limit yourquestions to not more than three orfour per letter, and send one couponfor each question. Please write clearly;use a typewriter if you have one, or atleast pen and ink and white paper. Wehave a "dead letter" file containing doz-ens of letters that cannot be answeredbecause names or addresses, or both.have been omitted, or the writing is un-decipherable, or the language is one thatno scholar can identify.
* * *
Many owners of the MANUAL evident-ly have not read the first section of thebook, which contains a wealth of prac-tical service data that answers many oftheir everyday service problems. Forintance, we have had dozens of requestsfor the R.M.A. standard color code, yetthis is fully explained on page 117. Takean evening off sometime and study thesection from page 5 to 129. You'll besurprised to see how much you canlearn.
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Past issues of RADIO Quin. have con-tained articles describing servicing in-struments of various kinds. The fol-lowing list should be remembered forreference. Back copies of the magazinecost 25 cents each and may be obtainedfrom RADIO CRAFT, 98 Park Place, New
RRCA -VICTOR, Inc.
Model R-6 Console . 326HModel R -12.326I to 326MModels R-20 and R-21 326N to 326PModel RAE -59 326Q, 326R
York, N. Y. Specify the issue you want.
"How to Test the Pentodes",155. September, 1931.
"Modernizing the Jewell 133A Analyz-er", page 211, October, 1931.
"Magic in Meters", November andDecember, 1931, and January, 1932.(These articles tell everything you wantto know about shunts and multiplierifor all kinds of meters.)
"Vacuum Tube Voltmeter", page 466,February, 1932.
"The Supreme Diagnometer", Febru-ary, March and April, 1932.
"Short -Checkers and Pre -Heaters",page 474, February, 1932, and page 535,March, 1932.
"A Service Test Panel for the Shop",page 533, March, 1932.
"Improving the Weston 537 Analyz-er", page 605, April, 1932.
"Combination Oscillator and TubeTester", page 586, April, 1932.
"Constructing a Simple Set Tester",page 659, May, 1932.