FM STEREO MR 71 TUNER - Berner's2003-3-1 · fm stereo tuner mr 71 contents table of contents owner's manual introduction technical description front panel information back panel

FM STEREOTUNER MR 71

CONTENTS

TABLE OF CONTENTS

OWNER'S MANUAL

INTRODUCTION

TECHNICAL DESCRIPTION

FRONT PANEL INFORMATION

BACK PANEL INFORMATION

INSTALLATION

CONNECTINGAudio OutputsStereophonic FM MultiplexMonophonic FMRemote AmplifiersOff-The-Air RecordingAntenna Connections

OPERATING INSTRUCTIONSStereophonic FM MultiplexMonophonic FM

ADJUSTMENTSMuting ThresholdDial Panel LightsOutput Adjust

GUARANTEE

MR

71

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THANK YOU

Judging from the stereo equipment you own, you rank highamong discriminating music listeners. You are probably nofreshman when it comes to stereo. Never-the-less we ask youto read and carefully follow these instructions to insure asuccessful partnership between you and your new stereoequipment.

You now have "THE BEST." Used properly you are in forthousands of hours of musical enjoyment.

If you are in a hurry, read page 3 first. This gives you a briefoutline of what each control and indicator does. Reading timefor this manual is 30 minutes. This is time well spent.

MR 71 FM STEREO TUNER

INTRODUCTION

The Mclntosh MR 71 is a precision engi-neered, highly sensitive FM Multiplex Tuner.

The research staff of Mclntosh Laboratoryhas developed five new tuner circuit improve-ments for the MR 71.

1. Automatic stereo-mono switching thatis "clickless" and completely electronic.(Patent applied for.)

2. Multipath indicator to eliminate multi-path reception by showing when your anten-na is rotated to the correct position for mini-mum multipath distortion.

3. Double tuned input circuits before thefirst R.F. amplifier to reduce spurious re-sponses.

4. New D'Arsonval movement meters ofincreased sensitivity which do not need zerosetting adjustments.

5. A new computer designed filter to re-duce noise from stations broadcasting sub-carrier auxiliary music services. No othertuner uses such a filter.

The MR 71 also uses the exclusive Mc-lntosh PANLOC method of installation. ThePANLOC system gives you absolute ease ofinstallation, operation, and maintenance.

PANLOC is the first professional installationtechnique to be used on stereo instruments.

In the PANLOC system a metal shelf ismounted first. The tuner slides into positionon this shelf. Depressing the PANLOC but-tons on the front panel locks the tuner firmlyinto place for normal operation. To unlockthe tuner depress the PANLOC buttons asecond time. The tuner can now slide fromthe front panel. The tuner will lock into thisposition, preventing accidental release ofthe tuner from the installation. Depressingthe holding latches allows the tuner to betaken out of the PANLOC shelf or to slideback into position against the mounting panel.

The finest possible reception of FM mono-phonic and FM multiplex stereophonic broad-casts is assured by the Mclntosh MR 71tuner.

Once you have enjoyed the outstandingperformance of the MR 71, you will under-stand why Mclntosh products have earnedtheir reputation as "THE BEST." Your Mc-lntosh MR 71 tuner will give you years of thefinest possible FM reception, and will be avalued part of your home music system.

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TECHNICAL DESCRIPTION

The MR 71 tuner has a 6DS4 high-grainNuvistor for the first RF amplifier. The Nuvis-tor (triode) operates into a second triode tubeto form a cascade amplifier. Careful designof the operating characteristics allows thecascade amplifier to handle a wide dynamicrange of signals with excellent signal-to-noise ratio.

A double-tuned RF input circuit combinedwith the Nuvistor-tube cascade amplifierreduces spurious signals to an extremely lowvalue. Sensitivity is increased to the highestpossible rating, while still retaining highselectivity.

A newly developed Automatic FrequencyControl (AFC) circuit greatly simplifies tuning.As the tuning knob is moved, the AFC circuitautomatically cuts off for sharpest tuning.After the station is tuned in, the AFC circuitgradually comes into operation over a 3second interval. The AFC action automaticallybrings the tuning to minimum distortion. Thisautomatic tuning repeats its action eachtime the tuning dial is moved to a new sta-tion. The amount of AFC action is fully ad-justable with a front panel control.

The AFC circuit is unique. It uses a silicondiode in place of a conventional tube. Thesilicon diode improves the overall AFC per-formance. It is unaffected by temperaturechanges. It has no warm-up drift and elimi-nates the chance of tube filament hum. Atemperature-compensated narrow band de-tector supplies operating signals to the AFCcircuit. This insures positive AFC action. Thenarrow band detector also operates the FMtuning meter amplifier and the ultrasonicmuting circuit.

The Mclntosh developed ultrasonic mutingcircuit automatically suppresses all intersta-tion noise, including the noises usually heardtuning in and out of a station. Weak or distantstations that can't override the backgroundnoise and interference are suppressed by themuting. A front panel switch allows muting tobe cut off for listening to weak and noisystations. A back panel adjust control is fac-tory set to the correct muting threshold level.

The mixer output is amplified through fiveintermediate frequency stages with flat-topped highly selective response curves.The IF transformers have wide band re-sponse with maximum adjacent channelrejection. Construction of the IF transformersassures electrical stability and resistance tomechanical shock and vibration. More thanadequate gain is provided to operate bothlimiters on the weakest signals. Two com-plete limiters are used for the best possiblesignal-to-noise ratio.

A separate wide band detector handlesonly audio frequencies for low distortion andwide frequency response.

Both the RF and IF circuits are completelyshielded in excess of FCC requirements forsuppression of radiation of the FM oscillatorand IF frequencies.

The MR 71 multiplex decoder uses aMclntosh developed detector. The advantageof this circuit is the elimination of criticaladjustments necessary with commonly usedmultiplex matrixing methods. The L-R (leftminus right) stereo sidebands are detected.Then automatically combined with the L+Rmain carrier signal. The left and right chan-nel signals are then produced with excellentseparation.

A temperature stabilized 19KC amplifierlocks in a highly stable 38KC synchronousoscillator. This method gives exceptionalnoise immunity. Balanced detectors cancelthe 38KC signal components in the output,providing low distortion and reduced sus-ceptibility to spurious signals. Tape record-ing interference is minimized by this method.

A highly selective computer designed filterreduces noise from stations broadcastingauxiliary music services. The filter reducesthe frequency band from 63-74KC approxi-mately 50db. The filter response slope is275db per octave. The noise is eliminatedwithout affecting normal program material.

The MR 71 has a multiplex stereo indicatorwhich lights when the dial pointer crosses astation broadcasting multiplex stereo. Aunique circuit using a transistor operates the

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Your Mclntosh MR71 tuner will give you many years of pleasantand satisfactory performance. If you have any questions concern-ing the operation or maintenance of this tuner please contact:

Customer ServiceMclntosh Laboratory Inc.2 Chambers StreetBinghamton, New York

Our telephone number is 723-5491.The direct dial area code is 607.

GUARANTEE

Mclntosh Laboratory Incorporated guar- period of 90 days from date of purchase,antees this equipment to perform as adver- This guarantee does not extend to compo-tised. We also guarantee the mechanical and nents damaged by improper use nor does itelectrical workmanship and components of extend to damage incurred during transpor-this equipment to be free of defects for a tation to and from Mclntosh Laboratory, Inc.

3-YEAR FACTORY SERVICE CONTRACT

An application for a FREE 3-YEAR FAC- fined in the 3-year factory service contract.TORY SERVICE CONTRACT is included in the If the application is not mailed to Mclntoshpocket in the back cover of this manual. The Laboratory, only the services offered underFREE 3-YEAR FACTORY SERVICE CONTRACT the standard 90-day guarantee will apply onwill be issued by Mclntosh Laboratory upon this equipment. TAKE ADVANTAGE OF 3receipt of the completely filed out applica- YEARS OF FREE FACTORY SERVICE BYtion form. The term of this contract is de- FILLING IN THE APPLICATION NOW.

Design subject to change without notice.

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MPX stereo indicator lamp. The transistor iscontrolled by a noise-rejecting differentialdetecting bridge circuit. The circuit discrimi-nates between noise and the 19KC multiplexpilot signal. The indicator will light only onthe 19KC signal present in a multiplex stereobroadcast.

The MR 71 uses a new Mclntosh developedautomatic mono-stereo switching circuit.(Pat. Pend.) The switching is electronic with-out switching clicks or transients.

The circuit switches smoothly and silentlywhen the 19KC multiplex carrier is present.

The multipath signal indicator on the tun-ing dial is an electron ray tube. This is anexclusive Mclntosh development. Multipathsignal reception causes moderate to severedistortion and poor stereo channel separa-tion. By knowing the presence of multipathreception, a directional FM antenna may berotated to reduce or eliminate the multipathsignal. The MR 71 multipath indicator shows

if there are multipath signals present byrapid fluctuation of the electron ray beams.

With the antenna correctly positioned, theindicator beams remain relatively steady,showing that multipath distortion has beeneliminated.

Two pairs of audio output jacks are on theback panel. One pair of jacks is controlledonly by the front panel volume control. Theother pair of jacks is controlled only by theback panel output adjust controls. Two stagefeedback type preamplifiers on both chan-nels provide low impedance outputs. Morethan sufficient output volume is available tofeed power amplifiers as well as preamplifiers.

A new type of mechanical tuning assemblygives the MR 71 extremely smooth flywheeltuning action. The tuning capacitor is drivendirectly, and in turn drives the pointer. Back-lash is eliminated with this design. A teflonlined pointer carriage and nylon pulleys re-duce friction and wear to give an unusuallysmooth and quiet dial action.

IF YOU ARE IN A HURRYTurn antenna so the eye is steady.

Will light only on stationsbroadcasting MPX stereo,

Tuning . . . selectdesired station

Tune for center of black area.

In . . . eliminates interstationnoise. Out . . . use to receiveweak stations.

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Continuously variable, useMax. position for MPX reception.automatically from stereo to mono.

Power off. Use stereo-autoposition: will switch

Tune for Max. reading.

Adjust to desired volume.

SPECIFICATIONS

Useable Sensitivity2.5 microvolts at 100% modulation (±75KCdeviation) for less than 3% total noise andharmonic distortion in accordance withIHF standards.

Audio Frequency ResponseWithin ½db from 20 to 20,000 cycles.

DistortionLessthan0.5%at 100% modulation ±75KCdeviation

Capture Ratio1.5db at 100% modulation.

MutingIF injected ultrasonic muting: at least 60dbnoise reduction between stations.

Oscillator DriftLess than 25KC with AFC disabled; negli-gible with AFC in operation.

Image RejectionBetter than 80db at 90MC; better than70db at 105MC.

HumBetter than 70db below 100% modulation.

OutputApproximately 2.5 volts; low impedance.

Antenna Inputs300 ohms balanced; 75 ohms unbalanced.

RF AmplifierCascode with 6DS4 Nuvistor in first stage.

IF StagesFive, with 200KC bandwidth, flat topresponse.

LimitersTwo.

RadiationSubstantially below FCC requirements.

Multiplex Channel SeparationBetter than 30db at 1000 cycles.

Multiplex FilterGreater than 48db suppression of 19KCpilot and 38KC carrier.

Multiplex IndicatorFront panel multiplex stereo light activatedby 19KC carrier-only.

Multiplex TypePeak-detecting, self matrixing detector.

SCA Filter50db down at 67KC to 74KC 275db peroctave slope.

Automatic Mono-Stereo SwitchAn exclusive Mclntosh development; all-electronic automatic mono-stereo switch-ing circuit. (Pat. Pend.).

Tube and Semiconductor Complement1-6DS4 Nuvistor, 1st RF.1-12AT7, 2nd RF and Mixer.1-6BN4A, Oscillator.1-6AU6, 1st IF.1-6AU6, 2nd IF.1-6AU6, 3rd IF.1-6AU6, 4th IF and 1st Limiter.1-6CS6, 5th IF 2nd Limiter and Muting.1—6BN8, Muting Amplifier, Muting

Detector, AVC Clamper.2-6BL8, Left and Right, 1st and 2nd

Audio Amplifiers.1-6U8, MPX Amplifier, MPX Indicator

Control.1-6HU6/EM87 Multipath Indicator.1-12AU7, MPX Oscillator.1-ST2-275, Voltage Reference.1-MA113 (Transistor), MPX Indicator

Lamp Switch.2-1N542 Diodes, Wide Band

Discriminator.2—1N542 Diodes, Narrow Band

Discriminator.4-1N542 Diodes, Balanced MPX

Detector.2-1N542 Diodes, Balanced Detector for

MPX Indicator.2—Selenium Rectifiers, High Voltage

Power Supply.1-No. 1850 Lamp, MPX Indicator.

Power Consumption70 watts, 105 to 125 volts, 50 to 60 cycles.

DimensionsFront Panel; 16 inches wide by 57/16 incheshigh; chassis (including PANLOC shelf) 15inches wide by 5 inches high by 13 inchesdeep, including connectors; clearance infront of mounting panel including knobs.1½ inches.

WeightChassis only, 27 pounds.In shipping carton, 37 pounds.

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FRONT PANEL INFORMATION

TUNING DIAL SCALESThe MR 71 has two dial scales, the 88 to

108 scale marked in megacycles and the0-100 logging scale. The dial scale markedin megacycles indicates the positions of FMstations in the 88 to 108 megacycle band.The logging scale with linear divisions from0-100 is located directly beneath the 88 to108 scale. The logging scale can be used toaccurately retune any station. You may findit easier to keep a record of your favoritestations by use of the logging scale.

INDICATORSThe MR 71 has four indicators on the

dial panel: MULTIPATH indicator, SIGNALSTRENGTH indicator, STEREO indicator, andthe TUNING indicator.

MULTIPATH INDICATORThe MR 71 MULTIPATH indicator is an ex-

clusive Mclntosh development.The MR 71 MULTIPATH indicator makes it

possible to improve FM reception withprecise FM antenna positioning.

Reduce noise due to multipath reception.Reduce distortion due to multipath recep-

tion.Improve stereo separation and the accu-

racy of your STEREO INDICATOR by reducingmultipath reception.

The MR 71 MULTIPATH INDICATOR showsdistortion from multipath signal reception.Multipath reception causes the two beams onthe indicator to fluctuate rapidly. When theantenna is rotated to the correct position,the indicator beams will remain steady. The

directional antenna is picking up only thedesired signal and rejecting the reflectedmultipath signals. In some locations, it ispossible that the best reception will occur ona strong reflected signal rather than thedirect signal. When you tune to a differentstation, the multipath indicator will tell youif multipath is present. Multipath is inde-pendent of signal strength.

STEREO INDICATORThe stereo indicator will light when the dial

pointer crosses a station broadcasting multi-plex stereo. The special circuit used will lightONLY on the 19KC multiplex carrier. Theindicator will not light on noise pulses orinterference.

TUNING INDICATORAn FM station is correctly tuned when the

indicator is in the black area of the tuningindicator. The action of the TUNING indicatoris independent of station signal strength.

VOLUME

Controls volume level when the tuner isconnected to the pair of jacks markedFRONT PANEL CONTROLLED.

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MODE SELECTORPOWER OFF

Turns off the tuner AC power and the ACoutlet on the tuner back panel.

MONO

Provides monophonic FM at both pairs ofleft and right channel audio output jacks.

brings the tuning to minimum distortion. TheAFC action repeats itself each time the tuningdial is moved to a different station.

The amount of AFC action is adjustablewith the AUTO FREQ. CONTROL. Full left(MIN) position of the control cuts off AFCaction. Full right (MAX) position gives maxi-mum AFC action.

Normally, the best tuning occurs with theAUTO FREQ. CONTROL set at or near MAXposition. If several stations are very closetogether on the dial, or if a desired station isvery close to a much stronger station, a lowerAFC setting is usually needed for best tuning.

MUTING

STEREO AUTO

The STEREO AUTO position provides bothmonophonic FM and FM multiplex stereo atthe left and right channel audio output jacks.Assume you have the MR 71 MODE SELEC-TOR in the STEREO AUTO position. You arelistening to a station broadcasting FM mono-phonic. The station switches to MPX stereobroadcast. The MULTIPLEX indicator willlight. The MR 71 will automatically switch toFM multiplex stereo operation. If monobroadcasting is resumed the MR 71 willautomatically switch to FM monophonic.

AUTO FREQ. CONTROL

The Automatic Frequency Control (AFC)circuit makes FM tuning easier. It eliminatesthe possibility of tuner drift. The AFC circuitin the MR 71 is electronically delayed in itsaction. This is an exclusive Mclntosh devel-opment. When the tuning dial is moved, theAFC circuit is temporarily cut off. When thedial pointer comes to rest on a station theAFC gradually comes into operation. Thistakes three seconds. The AFC automatically

OUT

OUT—This position turns off the muting toallow conventional tuning with interstationnoise present. Use this setting to listen toweak or distant stations that have noise orinterference.

IN—This position turns on the muting cir-cuit. Muting suppresses all background hissand noise usually heard when tuning be-tween stations. Weak or distant stations thatcannot override the background noise andinterference are suppressed by the muting.

PANLOC BUTTONS

At the bottom of the front corners are thePANLOC buttons. After a tuner is installed onthe PANLOC shelf, depressing the PANLOCbuttons will lock the tuner firmly in position.Depressing the PANLOC buttons a secondtime (as with a ball-point pen> will release thetuner. The tuner can then be slid forward tothe inspection and adjustment position. ThePANLOC system gives you absolute ease ofinstallation, operation and maintenance.

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BACK PANEL INFORMATION

TP 2

Test point TP 2 is provided for tuner circuitalignment. It is also used in conjunction withthe Mclntosh Ml 2 or Ml 3.

OUTPUT ADJ

This dual concentric control adjusts theoutput volume levels at the left-hand pair ofAUDIO OUTPUT JACKS. The center shaftadjusts the LEFT channel output, and theouter sleeve adjusts the RIGHT channel out-put. These output control settings for the leftpair of jacks are not affected by the MR 71front panel volume control.

MUTING ADJ

Adjust the operating threshold of the ultra-sonic muting circuit.

AUDIO OUTPUT-LEFT-RIGHT

The left-hand pair of AUDIO OUTPUT jacksprovides audio signals unaffected by theMR 71 front panel VOLUME control. The dualconcentric OUTPUT ADJUST controls set thevolume levels. Use these output jacks to con-nect the tuner to a stereo control preampli-

fier which has its own master volume control.

The right hand pair of AUDIO OUTPUTjacks provides audio signal controlled by theMR 71 front panel VOLUME control. Usethese output jacks to connect to externalpower amplifier, tape recorders, or anyequipment which requires continuous frontpanel control of tuner output volume.

300 OHM-75 OHM ANTENNATerminal for connecting FM antennas to

the MR 71.

1A SLO BLO FUSEA 1 amp "Slo-Blo" fuse protects the tuner

circuits. This fuse does not protect additionalequipment connected to the back panel ACoutlet.

AC OUTLETProvides 117 volt AC power up to 350 watts

maximum for additional equipment such asturntables, or other tuners. This outlet is notfused. It turns on and off with the front panelMODE SELECTOR switch.

PANEL LIGHT SWITCHAdjusts the panel lights to bright or dim.

INSTALLATION

The Mclntosh MR 71 tuner may be in-stalled on a table, on a shelf, in a custombuilt-in cabinet, or in a professional equip-ment rack. For best appearance in an openinstallation, mount the MR 71 in the attrac-tive Mclntosh L11 cabinet. The L12 is oiledwalnut. The L11 is lacquered walnut.

The MR 71 tuner is installed by the newexclusive Mclntosh PANLOC method. Referto the special PANLOC SYSTEM INSTALLA-TION instructions included with your MR 71.

Allow at least 13¾ inches behind the mount-ing panel for the MR 71 chassis. This in-cludes clearance for leads and connectors.Allow inside dimensions of at least 16½inches in width and 6 inches in height foradequate air circulation. The back of theMR 71 cabinet should be as open as possiblefor the best ventilation. Avoid mounting thetuner directly over a power amplifier. Theheat from the amplifier may change theprecision tuner calibration. Adequate ventila-tion will give your tuner long trouble-free life.

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CONNECTING

AUDIO OUTPUTSUse the FIXED OUTPUT jacks (left-hand

pair of jacks next to OUTPUT ADJ) to connectto a conventional control preamplifier whichhas its own volume control. Full tuner outputis available at all times from the FIXEDOUTPUT jacks.

Use the FRONT PANEL CONTROLLED jacksto connect to a conventional control pre-amplifier when continuous front panel con-trol of tuner volume is desired. These jacksmay be used to connect to external equip-ment such as power amplif iers or taperecorders where control of tuner volume isnecessary. There is no difference in thesignal quality or output levels available ateach pair of output jacks.

STEREOPHONIC FM MULTIPLEXConnect a shielded cable from the tuner

LEFT channel AUDIO OUTPUT jack to thecontrol preamplifier LEFT channel tuner orauxiliary input jack.

Connect a second shielded cable from theRIGHT channel tuner AUDIO output jack tothe control preamplifier RIGHT channeltuner or auxiliary input jack. When the MR 71mode selector is set to MONO or STEREOAUTO position, a monophonic broadcast willautomatically be present at both left andright outputs. For a stereo broadcast set theMODE SELECTOR in the STEREO AUTOposition.

MONOPHONIC FMThe MR 71 can be used strictly for mono-

phonic reception.Connect a shielded cable from either the

left or right audio output jack to the mono-phonic control preamplifier auxiliary or tunerinput jack. With the MR 71 MODE SELECTORset to MONO, the monophonic FM signalappears at both the left and right channelAUDIO OUTPUT jacks.

REMOTE AMPLIFIERSThe pair of audio output jacks not being

used in an installation may be connected toexternal or remote amplifiers. An FM pro-

SEE DIAGRAM

gram can then be fed to speaker systemsapart from the main sound system.

OFF THE AIR RECORDINGTape recorders or tape decks with record-

playback preamplifiers are normally con-nected to the Tape Output jacks on the con-trol preamplifier. Any FM program comingthrough the tuner into the preamplifier canbe recorded on tape. You may also connectthe extra pair of tuner audio output jacksdirectly to the recorder inputs if desired.

ANTENNA CONNECTIONSSatisfactory FM multiplex stereo reception

requires 10 times as much signal as FMmonophonic reception. Monophonic installa-tions that were satisfactory with an indoorFM antenna may require an outside or direc-tional FM antenna for satisfactory multiplexstereo reception. A good directional antennawith a rotator makes it possible to eliminateor minimize multipath distortion. The MR 71multipath indicator shows the correct an-tenna position for reception with minimummultipath distortion.

INDOOR FLEXIBLE FM DIPOLE

A convenient flexible indoor FM dipole(300 ohm) antenna is supplied with theMR 71 tuner. This antenna is easy to install.It is suitable for a good FM reception in highsignal areas.

Connect the two leads of the dipole an-tenna to the two terminals marked 300OHM on the MR 71 back panel.

The flexibility of the thin flat wire allows thedipole to be easily located behind the equip-ment enclosure or any position near thetuner. Open the dipole into a "T." Extend the

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arms as straight as possible. The dipoleantenna is somewhat directional. It should bepositioned for best reception of the desiredstations.

Experimenting with the dipole position maybe necessary to reduce multipath distortionon certain stations. Since it is not convenientto continually change the position of thedipole, you may have to set it for minimummultipath on your favorite station.

IMPORTANTKeep the dipole away from largemetal objects or surfaces. They inter-fere with the efficiency of the antenna.

An outdoor FM antenna is recommendedfor best FM reception under all conditions.In fringe areas, a highly directional FM an-tenna used with a rotator will give the finestpossible FM reception. Rotate the antennauntil it points in the direction of the station oruntil it receives the best possible signal. Usethe multipath, signal strength and tuningindicators to position the antenna correctly.

75 OHM ANTENNA

OUTDOOR FM ANTENNA

An unbalanced 75 ohm FM antenna can beused with the MR 71. A BNC connector isprovided. Connect a Male BNC connectorto the female BNC connector on the rearpanel of the MR 71.

OPERATING INSTRUCTIONS

STEREOPHONIC FM MULTIPLEX

1. Turn the MODE SELECTOR to STEREOAUTO.

2. Turn MUTING to IN.

3.Turn the FM TUNING dial to the desiredstation.

The TUNING indicator pointer should be inthe black area of the tuning indicator meter.When the MPX STEREO indicator is lit, thestation is broadcasting a 19KC carrier formultiplex stereo. The MR 71 will automati-cally switch to stereo Mode. If a station isbroadcasting monophonic FM program, theMPX STEREO indicator will remain off andthe tuner will automatically switch to MonoMode.

4. Adjust the volume control to desiredlistening level.

If the fixed audio output jacks are used, thetuner volume control will not affect volume.

MONOPHONIC FM

1. Turn the MODE SELECTOR to MONO tolisten only to monophonic FM.

Note: If you wish to receive monophonicFM and have the MR 71 automatically switchto a stereo broadcast available on the samestation set the MODE SELECTOR to STEREOAUTO.

2. Turn the MUTING to IN.

3. Turn the FM TUNING KNOB to thedesired station. The TUNING indicator pointershould be in the black area in the center ofthe indicator.

4. Rotate the directional antenna for bestreception as shown by the signal strengthand multipath indicators.

5. Adjust the VOLUME control to desiredlistening level.

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ADJUSTMENTS

MUTING THRESHOLD

The MR 71 ultrasonic muting circuit sup-presses all noise between stations. It sup-presses all weaker stations not strongenough to override the background noise.

The muting threshold setting determinesthe strength of the signal which can be heardwith muting in operation. The muting thresh-old is carefully adjusted to optimum at thefactory using precision test instruments.Casual adjustment of the muting thresholdis not recommended.

If it is necessary to adjust the mutingthreshold, use the MUTING ADJ control tothe RIGHT (clockwise) to lower the mutingthreshold. This allows weaker stations tobe heard with the MUTING IN SETTING.Turn the MUTING ADJ control to the LEFT(counterclockwise) to raise the muting thresh-old. This allows only the more powerfulstations to be heard with the MUTING INsetting.

DIAL PANEL LIGHT

Adjust the brightness of the dial panellights by means of the PANEL LIGHT switch

on the tuner back panel. Set the switch toBRIGHT for maximum panel light. Set theswitch to DIM for less dial light and extendedlamp life.

OUTPUT ADJUST

The dual concentric OUTPUT ADJ controls(on the tuner back panel) adjust the outputvolume level of the left hand pair of AUDIOOUTPUT JACKS. The center shaft of thecontrol adjusts the left channel output. Theouter sleeve of the control adjusts the rightchannel output.

Before making the adjustment, connectthe left hand AUDIO OUTPUT jacks to thetuner inputs of the control preamplifier. Setthe preamplifier selector to phono. Set thevolume control to normal listening level fora stereo disc recording. Switch the preampli-fier selector back to tuner. Set the MR 71MODE SELECTOR to MONO. Tune in a localstation. Tune the OUTPUT ADJ controlsuntil the levels of both channels are equal,and equal to the volume level of the phonorecording. You can now switch the preampli-fier selector from the MR 71 to other pro-gram sources without readjusting the mainvolume control.

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FM STATION LOG

STATION DIALFREQ.

LOGSCALE

LOCATIONCITY, STATE

ANTENNADIRECTION

REMARKSMONO-STEREO-TIME-DATE

FM STATION LOG

STATION DIALFREQ.

LOGSCALE

LOCATIONCITY, STATE

ANTENNADIRECTION

REMARKSMONO— STEREO— TIME— DATE

FM STATION LOG

STATION DIALFREQ.

LOGSCALE

LOCATIONCITY, STATE

ANTENNADIRECTION

REMARKSMONO— STEREO— TIME— DATE

2 CHAMBERS STREET, BINGHAMTON, N. Y.Made in U.S.A.

Phone-Area Code 607-723-5491

038-029

BE022003

Printed in U.S.A.

LABORATORY INC.