FM STEREO MR65B TUNER - akdatabase.org

FM STEREOTUNER MR65B

INTRODUCTION

TABLE OF CONTENTS

TECHNICAL DESCRIPTION.

FRONT PANEL INFORMATION

BACK PANEL INFORMATION

INSTALLATION

CONNECTING

Stereophonic FM Multiplex

Monophonic FM

Remote Amplifiers

Off-The-Air Recording

Antenna Connections

OPERATING INSTRUCTIONS.

Stereophonic FM Multiplex

Monophonic FM

External Stereo

ADJUSTMENTS

Muting Threshold

FM Signal Strength Meter

FM Tuning Meter

Dial Panel Lights.

Output Adjust

GUARANTEE

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MR65B FM STEREO TUNERINTRODUCTION

The Mclntosh Model MR65B is a precision-engineered, sensitive FM multiplex stereotuner. It offers the finest possible receptionof FM monophonic and FM multiplex stereo-phonic broadcasts. Every desirable featurefor your FM listening pleasure is included inthe MR65B tuner. It is perfect for use in astereo music system where nothing less than"THE Best" will do.

Once you have enjoyed the outstandingperformance of the MR65B, you will under-stand why Mclntosh products have earnedtheir reputation as "THE Best."

Your Mclntosh MR65B tuner will give youyears of the finest possible FM reception, andwill become a highly valued part of yourhome music system.

TECHNICAL DESCRIPTION

The MR65B tuner has a 6DS4 high-gainNuvistor for the first RF amplifier. The Nuvis-tor (triode) operates into a triode tube to forma cascode amplifier. Careful design of theoperating characteristics allows the cascodeamplifier to handle a wide dynamic range ofsignals with excellent signal-to-noise ratio.

A double-tuned RF input circuit combinedwith the Nuvistor-tube cascode 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 3 sec-ond interval. The AFC action automaticallybrings the electrical tuning to the correctpoint for minimum distortion. This auto-matic tuning repeats its action each time thetuning dial is moved to a different station.The amount of AFC action is fully adjustablewith a front panel control.

The AFC circuit is quite unique. It uses asilicon diode in place of a conventional tube.The silicon diode improves the overall AFCperformance since it is unaffected by tem-perature changes, has no warm-up drift andeliminates the chance of tube filament hum.A special temperature-compensated narrowband detector supplies operating signals tothe AFC circuit. This insures positive AFCaction. The narrow band detector alsooperates the FM tuning meter amplifier andthe ultrasonic muting circuit.

- The Mclntosh-developed ultrasonicmutingcircuit automatically suppresses all inter-station noise, including the noises usuallyheard tuning in and out of a station. Weak ordistant stations that don't over-ride the back-ground noise and interference are also sup-pressed by the muting. A switch on the frontpanel allows muting to be cut off for listeningto these weak and noisy stations. A backpanel adjust control is factory-set to theproper muting threshold level.

Three flat-topped response IF amplifiersreject adjacent channel interference. Morethan adequate gain is provided to operateboth limiters on the weakest signals. Twocomplete limiters are used to insure the bestpossible signal-to-noise ratio.

A separate wide band detector handlesexclusively the audio frequencies for low dis-tortion and wide frequency response.

Both the RF and IF circuits are com-pletely shielded and exceed the FCC require-ments for suppression of radiation from theFM oscillator and IF frequencies.

A unique multiplex stereo (MPX) indicatorlight is included on the front dial panel. TheMPX indicator lights whenever the dialpointer crosses a station broadcasting FMmultiplex stereo. The indicator uses a specialnoise-rejecting bridge circuit with two ger-manium diodes. The indicator lights ONLY onthe 19KC carrier present in a multiplex stereobroadcast. It will not light on noise or inter-ference signals.

The MR65B multiplex decoder circuituses a special peak-switching, self-matrixingdetector. Stereo channel separation is main-tained at better than 30db.

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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 MR65B an extremely smooth fly-wheel tuning action. The tuning capacitor isdriven directly, and in turn drives the pointer.Backlash is practically eliminated with thismethod of design. A teflon lined pointercarriage and nylon pulleys reduce frictionand wear to give an unusually smooth andquiet dial action.

SPECIFICATIONS

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

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

Distortion

Less than 0.5% 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; negligiblewith AFC in operation.

Image RejectionBetter than 80db at 90MC; better than 70dbat 105MC.

Hum

Better 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 AmplifiersFour, 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.

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, 2nd Limiter and Muting.1—6BN8, Muting Amplifier, Muting Detector,

AVC Clamper.2—6BL8, Left and Right, 1st and 2nd Audio

Amplifiers.1—12AU7, Balanced Tuning Meter Amplifier.1—6U8, MPX Amplifier, MPX Indicator Con-

trol.

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1-12AU7, MPX Oscillator.1—ST2-275, Voltage Reference.1—MA113 (Transistor), MPX Indicator Lamp

Switch.2—Diodes, Wide Band Discriminator2—Diodes, Narrow Band Discriminator.4—Diodes, Balanced MPX Detector.2—Diodes, Balanced Detector for MPX Indi-

cator.2—Rectifiers, High Voltage Power Supply.

Power Consumption

70 watts, 105 to 125 volts, 50 to 60 cycles.

Dimensions

Front panel 15-3/8inches x 5-1/8 inches; overalldepth of chassis behind front panel, 12-3/16inches; clearance in front of mounting panelincluding knobs, 1-1/2 inches.

Weight

Chassis only, 22 pounds.In shipping carton, 31 pounds.

FRONT PANEL INFORMATION

Figure 1. MR65B Front Panel.

TUNING DIAL

The tuning dial is calibrated in bothmegacycles and a 0-100 logging scale. Tun-ing back to a particular station is much easierby keeping a record of the exact station loca-tion on the logging scale.

METERS

Figure 2. FM Signal Strength Meter.

At the left side of the dial is the FM SIG-NAL STRENGTH meter. The amount of meterpointer deflection indicates the relative sig-nal strength of the station being received.Use the signal strength meter to correctlyposition a directional FM antenna. Maximummeter deflection for a particular stationoccurs when the antenna is pointed in thedirection for best signal pickup.

Figure 3. FM Tuning Meter.

At the right side of the dial is the FM TUN-ING meter. An FM station is correctly tunedwhen the meter pointer is within the blackarea at the center of the meter scale. Bothmeters can be adjusted for proper zero set-tings if necessary. (See section titled AD-JUSTMENTS.)

MULTIPLEX STEREO INDICATOR

At the center of the tuning dial is themultiplex stereo (MPX) indicator. The indi-cator lights (red) MPX whenever the dialpointer crosses a station broadcasting multi-plex stereo. The indicator lights ONLY on the19KC multiplex carrier present in a multi-plex stereo broadcast. The indicator willNOT light on noise or interference signals.

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VOLUMEControls the output volume level of the

tuner at the right hand pair of AUDIO OUT-PUT jacks on the back panel. This pair ofjacks is marked FRONT PANEL CONTROLLED.The other pair of audio output jacks, locatedto the left, is not affected by the front panelvolume control. The output volume level atthese jacks is controlled by the dual con-centric OUTPUT ADJ controls to their left.(See section titled ADJUSTMENTS.)

MODE SELECTOR

AUTO FREQ CONTROL

Figure 4. Mode Selector.

Power Off

Turns off the tuner AC power and also turnsoff the AC outlet on the tuner hack panel.

If a TV antenna is used for FM in the man-ner described under ANTENNA CONNEC-TIONS, it will automatically be switched backto the TV set in the POWER OFF position.

FM

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

MPX Stereo

Provides FM multiplex stereo at the respec-tive left and right channel audio output jacks.

EXT Stereo

Provides monophonic FM at the RIGHTchannel audio output jacks. The back panelEXT STEREO INPUT jack is also connectedthrough the tuner preamplifier to the LEFTchannel audio output jacks in this switchposition. A monophonic AM tuner, for exam-ple, may be connected to the EXT STEREOINPUT for AM-FM stereo reception.

Figure 5. Auto Freq Control.

The Automatic Frequency Control (AFC)circuit makes FM tuning easier. It also elimi-nates the possibility of the tuner drifting offthe station. The AFC circuit in the MR65B iselectronically delayed in its action. This is anexclusive Mclntosh development. As thetuning dial is moved, the AFC circuit is tem-porarily cut off. After the dial pointer hascome to rest on a particular station, the AFCgradually comes into operation over a threesecond interval. The AFC automatically bringsthe electrical tuning to the correct point forminimum distortion. This automatic tuningrepeats itself each time the tuning dial ismoved to a different station.

The degree 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 MAX posi-tion. If several stations are very close to-gether on the dial, or if a desired station isvery close together on the dial, or if a desiredstation is very close to a much stronger sta-tion, a lower AFC setting is usually necessaryfor best tuning.

MUTING

Figure 6. Muting Control.

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InTurns on the Mclntosh-developed ultrasonicmuting circuit. Ultrasonic muting suppressesall background hiss and noise and noiseusually heard when tuning between stations.Weak or distant stations that may not over-ride the noise and interference are also sup-pressed by the muting.

OutTurns off the ultrasonic muting to allow con-ventional FM tuning with inter-station noisepresent. Use this setting to listen to weak ordistant stations that may be mixed withnoise or interference.

BACK PANEL INFORMATION

Figure 7. MR65B Back Panel.

TP 2

A test point provided for convenience oftuner circuit alignment. Refer to the MR65BMaintenance Manual for complete alignmentprocedure and suggested test equipment.

OUTPUT ADJ

Dual concentric control adjusts the outputvolume levels at the left hand pair of AUDIOOUTPUT jacks. The center shaft adjusts theLEFT channel output, and the outer sleeveadjusts the RIGHT channel output. Theseoutput control settings for the left pair ofjacks are not affected by the MR65B frontpanel volume control. (See section titledADJUSTMENTS.)

MUTING ADJ

Adjusts the operating threshold of theultrasonic muting circuit. (See MUTINGADJUST under ADJUSTMENTS section.)

AUDIO OUTPUT-LEFT-RIGHTThe left hand pair of AUDIO OUTPUT

jacks provides FM signals unaffected by theMR65B 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 con-trol. This pair of jacks is recommended forMclntosh preamplifiers.

The right hand pair of AUDIO OUTPUTjacks provides FM signals controlled by theMR65B front panel colume control. Usethese output jacks to connect to externalpower amplifiers, tape recorders, or anyequipment which requires continuous frontpanel control of tuner output volume.

EXT STEREO INPUT

Connects through the MR65B left channelpreamplifier and appears at the left channelaudio outputs when the MODE SELECTOR isset to EXT STEREO. The MR65B monophonicFM output appears at the right channel audiooutput jacks when the MODE SELECTOR isset to EXT STEREO.

An AM tuner may be connected to theEXT STEREO INPUT for reception of AM-FMstereo in the EXT STEREO setting.

FM ANT

Terminals for connecting an FM antennato the MR65B.

TO TV SET

Terminals for connecting TV set antennaleads when a VHF TV Antenna is used forboth the MR65B and a TV set. The antenna isautomatically switched to the MR65B whenthe MODE SELECTOR switch turns theMR65B to any of the "ON" positions. The

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antenna is switched back to the TV set whenthe MR65B MODE SELECTOR is turned toPOWER OFF.

1A SLO BLO FUSE

A 1 amp "Slo-Blo" fuse protects the tunercircuits. This fuse does not protect additionalequipment connected to the back panelAC outlet.

AC OUTLETProvides 117 volt AC power up to 350

watts maximum for additional equipmentsuch as turntables or other tuners. This out-let is not fused and turns on and off with thefront panel MODE SELECTOR switch.

PANEL LIGHT SWITCHAdjusts the front panel lights to bright

or dim.

INSTALLATION

The Mclntosh MR65B 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, it is suggested that you mountthe MR65B in the attractive Mclntosh ModelL66 finished wood cabinet.

The MR65B may be mounted in panels upto 1 inch in thickness. If the panel is at least¼ inch or more in thickness, the tuner will beadequately supported by the four front panelmounting screws. In cases where the frontpanel may be thin or flexible, a shelf is neces-sary to support the weight of the tuner. Ashelf is not required when the MR65B ismounted in a metal rack panel.

An MR65B cabinet installation shouldprovide at least 13¾ inches behind themounting panel for clearance of leads andconnectors. Allow inside dimensions of atleast l6½ inches in width and 5 inches inheight for adequate air circulation. The backpanel of theMR65Bcabinet should be left asopen as possible for best ventilation. Avoidmounting the tuner directly over a poweramplifier. The heat from the amplifier outputtubes may affect the precision tuner calibra-tion. Adequate ventilation will insure yourtuner a long and trouble-free life.

CUTTING THE FRONT PANELThe PANEL CUTOUT TEMPLATE supplied

with your tuner is a full size layout of thefront panel cutout and mounting holes. Thetemplate is positioned accurately on thecabinet front by drilling two locating holesthrough from the back side of the panel. Allmeasurements for panel cutout location aremade on the back side of the panel. One ofthe two end mounting strips supplied withthe tuner (3½ inches by ½ inch) makes aconvenient measuring tool for determiningthe exact positions of the locating holes.

Determine the exact center of the pro-posed panel cutout area. Scribe a verticalline at the center, from the top surface of themounting shelf to the top of the panel asshown in "A" of Figure 8. Using one of themounting strips as a measuring tool, scribe ahorizontal line 3½ inches above the top sur-face of the mounting shelf as shown in "B"of Figure 8. Again using the mounting strip,mark a point on the horizontal line 3½ inchesto the left of the center line. Mark a secondpoint 3½ inches to the right of the centerline. These two points should be 7 inchesapart, 3½ inches above the mounting shelfand 3½ inches to each side of the vertical

Positions "A" to "C" show the location of thevertical center line, the use of the measuringtool (mounting strip) to locate the horizontalcenter line, and how to measure off the twopoints to the right and left of the vertical centerline.

Figure 8. Front Panel Cutout Measurements.

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center line. See "C" of Figure 8. Drill a 3/16inch diameter hole through the back of thepanel at each of the two points. Make certainthat you hold the drill perpendicular to thepanel so the holes will be accurately locatedon the front side of the panel.

Using the previously drilled locating holesfor correct alignment, carefully position thecutout template on the front panel.

Scribe the rectangular cutout on the frontpanel and mark the positions of the sixmounting holes. Drill the six 3/16 inch diametermounting holes before cutting the panelopening. Next cut the main panel opening. Itis important that the cutout be just within theheavy black lines on the template.

SHELF MOUNTING

Locate the exact center of the proposedshelf area and scribe a line from the front tothe back of the shelf. The SHELF CUTOUTTEMPLATE is marked for front panel thick-ness from ¼ inch to 1 inch. Fold the templateon the line that corresponds to the thicknessof the particular panel being used. Place thefolded template on the shelf, butted againstthe back side of the front panel. Match thecenter line on the template to the scribedcenter line on the shelf. The shelf center lineshould also exactly meet the vertical centerline used to make the front panel cutout.Mark the positions of the four ¼ inch diame-ter mounting holes. Scribe the rectangularcutout for the ventilating hole. Drill the four¼ inch diameter mounting holes and thencut out the rectangular ventilating hole.

INSTALLING THE MR65B

Remove the four 10-32 x % inch screwsholding the MR65B to the shipping board.Save these screws since you will need themif your cabinet shelf is ½ inch or 5/8inch thick.Remove the four plastic feet from the bottomof the tuner.

The mounting hardware package includesfour 6-32 flat head screws and eight 6-32round head screws. Two of the flat headscrews of the proper length are used to at-tach the mounting strips to the cabinet panel.Four of the round head screws of the properlength are used to attach the tuner to themounting strips and the cabinet panel.The 6-32 x ½ inch screws are used with

panels under 3/8 inch thickness. The 6-32 x1¼ inch screws are used with panels from3/8 inch to 1 inch thickness.

The edge of the strip with the clips mustface toward the panel opening. Line up themounting strips on each side of the panel cut-out so the three holes in the strips are in linewith the holes in the panel. Install two of theproper length flat head screws through thefront panel and into the center hole of eachmounting strip. Drive the screws in so the flatheads are flush with the panel. If necessary,countersink the two center holes.

Figure 9. Securing the Mounting Strip to Front Panel.

Carefully insert the tuner through thefront panel opening so it rests on the sup-porting shelf. Insert the proper length roundhead screws into the four holes in the mount-ing flanges on each end of the tuner panel.Drive the screws in through the panel andinto the threaded clips on the mountingstrips. Do not tighten these screws yet.

If the cabinet is fixed and will not bemoved about, it is not necessary to securethe tuner chassis to the shelf. If the cabinetis to be moved about, it is recommendedthat the tuner chassis be secured to theshelf in the following manner.

Tighten the four screws holding the tunerto the front panel. The four 10-32 x % inchscrews used in shipping the tuner are alsoused to mount it to a shelf of ½ inch or 5/8inch thickness. Use the 10-32 x ½ inchscrews if the mounting shelf is 3/8 inch thick-ness or less. Use the 10-32 x 1 inch screws ifthe shelf is ¾ inch or 7/8inch thickness.Secure the chassis with the proper length

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10-32 screws by inserting them up throughthe holes in the shelf, and into the threadedholes in the tuner chassis bottom. Tightenthe 10-32 screws after you have first tight-ened the front panel screws.

IMPORTANT

Use of the wrong length 10-32screws may cause electrical short-ing in the tuner circuits.

Attach the two metal panel end caps(packed with the tuner) on each end of thetuner panel by sliding onto the pins. (SeeFigure 10.) The end caps are held by springtension and can easily be removed if thetuner is to be taken out of the cabinet.

MOUNTING IN THE L66 CABINET

The Mclntosh L66 cabinet is suppliedwith complete instructions and all necessaryhardware for installing the MR65B tuner. The

PUSH ON

Figure 10. Fitting of Panel End Caps to Panel.

dimensions of the L66 cabinet are 169/16inches wide by 6-11/16 inches high includingmounting feet by 13¾ inches deep includingtuner front panel and control knobs.

CONNECTING

Use the left hand pair of tuner AUDIOOUTPUT jacks for connecting to a conven-tional stereophonic control preamplifier. Theoutput volume levels at these jacks areaffected only by the tuner back panel dualconcentric OUTPUT ADJ controls. The lefthand pair of jacks is recommended when thetuner is used with a Mclntosh control pre-amplifier.

Use the right hand pair of AUDIO OUT-PUT jacks when you wish to use the tunerfront panel volume control. Use these jacksfor connecting directly to tape recorders,power amplifiers or any equipment withoutits own volume control.

There is no difference in the signal qualityor available output level at each pair of out-put jacks.

STEREOPHONIC FM MULTIPLEX

Connect a shielded cable from the propertuner LEFT channel AUDIO OUTPUT jack,to the control preamplifier LEFT channeltuner or auxiliary input jack.

Connect a second shielded cable from theproper RIGHT channel tuner AUDIO OUTPUTjack to the corresponding control preampli-fier RIGHT channel tuner or auxiliary inputjack.

Suitable shielded cables are suppliedwith the tuner.

MONOPHONIC FM

Connect a shielded cable from the proper

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tuner left or right audio output jack to themonophonic control preamplifier tuner orauxiliary input jack. With the tuner MODESELECTOR set to FM, the monophonic FMsignal appears at BOTH the left and rightchannel AUDIO OUTPUT jacks.

REMOTE AMPLIFIERS

The two AUDIO OUTPUT jacks not beingused in an installation may be connected toexternal or remote amplifiers. FM programscan then be fed to speaker locations apartfrom the main sound system.

OFF-THE-AIR RECORDING

Tape 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 comingfrom the tuner into the preamplifier canthen be recorded on tape. You may also con-nect the extra pair of tuner audio outputjacks directly to the recorder inputs if desired.

ANTENNA CONNECTIONSSatisfactory FM multiplex stereo reception

requires approximately 10 times as muchsignal from the antenna compared to equiva-lent FM monophonic reception. Monophonicinstallations that were satisfactory with anindoor FM antenna may require an outside ordirectional FM antenna for equivalent FMmultiplex reception.

Figure 11. MR65B Typical Hook-up.

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INDOOR FLEXIBLE FM DIPOLE

300 OHM INDOORDIPOLE FM ANTENNA

Figure 12. Connection of 300 Ohm IndoorDipole FM Antenna to MR65B.

A convenient flexible indoor dipole (300ohm) antenna is supplied with the MR65Btuner. This antenna is easy to install and issuitable for good FM reception in urban orhigh intensity signal areas.

Connect the two leads of the dipole an-tenna to the two terminals marked FM ANTon the tuner back panel. The flexibility of thethin flat wire allows the dipole to be easilylocated behind the equipment enclosure orin any convenient position near the tuner.Open the dipole into "T" and extend thearms as straight as possible. The dipoleantenna is somewhat directional and mayhave to be positioned in a particular locationfor best reception of desired stations.

IMPORTANT

Keep the dipole away from largemetal objects or surfaces sincethey may interfere with the effi-ciency of the antenna.

OUTDOOR FM ANTENNA

An outdoor FM antenna is always recom-mended for best FM reception under allconditions. In fringe or outlying areas espe-cially, a highly directional FM antenna usedin conjunction with a rotator will give thefinest possible FM reception. Rotate theantenna until it points in the direction of thestation or until it receives the best possiblesignal.

The FM signal strength meter aids inpositioning a directional antenna. Observethe meter indication for a given station as the

antenna rotates. The meter will indicate itshighest reading when the antenna is pointedin the direction for maximum signal pickup.

75 OHM ANTENNAFROM VHF TV

ANTENNA

TO TV SETFigure 13. Connection of 75 Ohm Antenna to MR65B.

An unbalanced 75 ohm FM antenna mayalso be used with the MR65B. Connect thecenter lead of the coaxial lead-in cable to theright hand FM ANT terminal. Connect theshield of the coaxial cable to the groundscrew next to this same FM ANT terminal.

VHF TV ANTENNA

Figure 14. VHF TV Antenna Connections.

A conventional VHF TV antenna of thetype also suitable for FM may be used withthe MR65B. Connect the two leads from the300 ohm TV antenna lead-in wire to the twoFM ANT terminals on the tuner back panel.Connect a length of 300 ohm flat lead-in wirefrom the TO TV SET terminals on the tunerback panel to the antenna terminals of theTV set.

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OPERATING INSTRUCTIONS

STEREOPHONIC FM MULTIPLEX

1. Turn the MODE SELECTOR to MPX STEREO.2. Turn the AUTO FREQ control to MAX.

Automatic Frequency control corrects theelectrical station tuning to the exact point forminimum distortion. An electronic delayturns on the Automatic Frequency controlover a 3 second interval after the dial pointerstops on a station. For all normal tuning, setthe AUTO FREQ CONTROL to MAX.

If stations are close together on the dial orif a desired station is close to a much strongerstation, reduce the AUTO FREQ CONTROLsetting for best tuning.3. Turn MUTING to IN.

Mclntosh Ultrasonic muting suppressesall background noise and hiss usually heardwhen tuning between stations. Use MUTINGIN for all normal tuning.

Weak or distant stations that don't over-ride the background noise and interferenceare also suppressed. Turn MUTING OUTto listen to these weaker stations.4. Turn the FM TUNING dial to the desired

station. The tuning meter should indicatein the center black area. If the red MPXindicator lights, the station is broadcastingmultiplex stereo. The MPX indicator lightsONLY when the tuner is receiving a stationbroadcasting FM multiplex stereo. Theindicator will NOT light on noise or inter-ference signals.If the same station broadcasts a regular

monophonic FM program, the MPX indicatorwill remain off.5. Adjust the appropriate volume controls,

depending on which pair of AUDIO OUT-PUT jacks is being used.The front panel VOLUME control operates

only with the pair of AUDIO OUTPUT jacksmarked FRONT PANEL CONTROLLED. Setthe VOLUME control to its mid position.

The OUTPUT ADJ controls on the backpanel pre-set the volume levels of the lefthand pair of AUDIO OUTPUT jacks. Turn theouter knurled sleeve for RIGHT channelvolume and the center knurled shaft for LEFTchannel volume. Set the OUTPUT ADJ con-trols to their mid positions. Make final volumeadjustments to balance the tuner volume

with the volume of a phono record playingthrough the control preamplifier.

MONOPHONIC FM1. Turn the MODE SELECTOR to FM.2. Turn the AUTO FREQ CONTROL to MAX.

(Adjust the same as for MPX reception.)3. Turn MUTING to IN.

(Set the same as for MPX reception.)4. Turn the FM TUNING dial to the desired

station. The tuning meter should indicatein the center black area.

5. Adjust the appropriate volume controls,depending on which pair of AUDIO OUT-PUT jacks is being used.(Adjust the same as for MPX reception.)

EXTERNAL STEREO1. Connect an external tuner to the back

panel EXT STEREO INPUT jack.2. Turn the MODE SELECTOR to EXT STEREO.3. Turn the AUTO FREQ CONTROL to MAX.

(Adjust the same as for MPX reception.)4. Turn the FM TUNING dial to the FM sta-

tion broadcasting one channel of a stereo-phonic broadcast. The tuning meter shouldindicate in center black area.(The FM broadcast appears in the RIGHTchannel.)

5. Tune the external tuner to the stationbroadcasting the other channel of thestereophonic broadcast. (The externaltuner program appears in the LEFT chan-nel.) The EXT STEREO function will mostoften be used for AM-FM stereophonicbroadcasts. The station broadcasts onechannel of a stereo program on the AMtransmitter and the other channel on theFM transmitter.

6. Adjust the appropriate volume controls,depending on which pair of AUDIO OUT-PUT jacks is being used.(Adjust the same as for MPX reception.)If the external tuner has a volume con-trol, adjust it to equal the volume levelof the MR65B.

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ADJUSTMENTS

MUTING THRESHOLD

TP 2

MUTINGADJ

OUTPUTADJ

MCINTOSH LABORATORY INC.BINGHAMTON. N.Y.

MADE IN USA

Figure 15. Muting Threshold

The MR65B ultrasonic muting circuitsuppresses all noise between stations. It alsosuppresses all weaker stations not strongenough to over-ride the background noise.

The muting threshold setting determinesthe strength of the signal which can beheard with muting in operation. The mutingthreshold is carefully adjusted to optimum atthe factory using precision test instruments.Casual adjustment of the muting thresholdis not recommended.

If it is found necessary to adjust themuting threshold, use the MUTING ADJcontrol on the tuner back panel. Turn theMUTING ADJ control to the RIGHT (clock-wise) to lower the muting threshold. Thisallows weaker, noisier stations to be heard atthe MUTING IN setting. Turn the MUTINGADJ control to the LEFT (counterclockwise)to raise the muting threshold. This allowsonly the more powerful stations to be heardat the MUTING IN setting.

FM SIGNAL STRENGTH METER

The FM SIGNAL STRENGTH meter pointershould normally rest on the zero scale mark-ing with FM operating but no station tuned in.

Figure 16. FM Signal Strength Meter

To adjust, turn the MODE SELECTOR toFM. Turn the MUTING control OUT. Turn theAUTO FREQ control to MIN. The volume con-trol has no effect on this adjustment. Turnthe tuning dial to a position NOT on or near astation. Allow the tuner to operate for ap-proximately 5 minutes. Rotate the red SIGSTH thumb wheel control (under the left dialpanel end cap) until the meter pointer iscentered on the zero scale marking.

FM TUNING METER

Figure 17 . FM Tuning Meter.

The FM TUNING meter pointer shouldnormally rest within the center black area ofthe scale when an FM station is properlytuned.

Check the tuning meter adjustment inthe following manner after the tuner hasbeen operating approximately 5 minutes.

Turn the MODE SELECTOR to FM. Turnthe AUTO FREQ CONTROL to MIN (counter-clockwise). The MUTING and VOLUME con-trols have no effect on this adjustment and

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may be set in any position. Tune to an FMstation until the meter pointer is exactly inthe center of the black scale area. Turn theAUTO FREQ CONTROL to MAX (clockwise).Wait a few seconds and watch the meterpointer to see if it moves off the center ofthe black scale area.

Adjust the brightness of the dial panellights by means of the PANEL LIGHT switchon the tuner back panel. Set the switch toBRIGHT for maximum panel light. Set theswitch to DIM for less dial light and extendedlamp life.

If the meter pointer changes position,adjust the red TUNING MTR thumb wheelcontrol (under the right dial panel end cap)until the meter pointer moves back to thecenter of the black area. Check the adjust-ment by repeating the procedure. Againturn the AUTO FREQ CONTROL back to MINand re-tune the station. Turn the AUTOFREQ CONTROL up to MAX and again checkfor meter pointer movement. Adjust thetuning meter thumb wheel control again ifnecessary to re-center the meter pointer inthe black area. If the meter pointer moves anappreciable amount on the first test, thesecond adjustment is necessary for precisemeter operation. When the meter circuit isproperly adjusted the meter pointer shouldstay centered in the black scale area whenthe AUTO FREQ CONTROL is turned fromMIN to MAX.

When the FM tuning meter is adjusted bythis procedure, precise FM tuning is insuredwith the meter pointer centered in the blackscale area. This procedure eliminates thepossibility of noise affecting the meteradjustment.

DIAL PANEL LIGHTS

105-125 V50-60 CPS70 WATTS

PANELLIGHT

OUTPUT ADJUST

TP 2

MUTINGADJ

OUTPUTADJ

MclNTOSH LABORATORY INC

BINGHAMTON NY

MADE IN USA

Figure 18. Dial Panel Lights.

Figure 19. Output Adjust

The dual concentric OUTPUT ADJ con-trols (on the tuner back panel) adjust the out-put volume level of the left hand pair ofAUDIO OUTPUT jacks. The center shaft ofthe control adjusts the left channel output.The outer sleeve of the control adjusts theright channel output.

To adjust, first connect the left handAUDIO OUTPUT jacks to the tuner inputs ofthe control preamplifier being used. Set thepreamplifier selector to phono and thevolume control to normal listening level for atypical stereo disc recording. Switch thepreamplifier back to the tuner. Set theMR65B MODE SELECTOR to FM and tune ina local station. Turn the tuner OUTPUT ADJcontrols until the levels of each channel areequal to each other and also equal to thevolume level of the previous phono record-ing. You can now switch the preamplifierselector from the MR65B to other programsources without need for readjusting themain volume control.

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Your Mclntosh MR65B tuner will give you many years of pleas-ant and satisfactory performance. If you have any questions con-cerning the operation or maintenance of this tuner, please contact

CUSTOMER SERVICEMCINTOSH LABORATORY INC.2 CHAMBERS STREETBINGHAMTON, NEW YORK

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

GUARANTEE

Mclntosh Laboratory, Inc. guarantees this equipment to per-form as advertised. We also guarantee the mechanical andelectrical workmanship and components of this equipment to befree of defects for a period of 90 days from date of purchase.This guarantee does not extend to components damaged byimproper use nor does it extend to damage incurred duringtransportation to and from Mclntosh Laboratory, Inc.

3-YEAR FACTORY SERVICE CONTRACT

An application for a FREE 3-YEAR FACTORY SERVICE CON-TRACT is included in the pocket in the back cover of this manual.The FREE 3-YEAR FACTORY SERVICE CONTRACT will be issuedby Mclntosh Laboratory upon receipt of the completely filled outapplication form. The term of this contract is defined in the3-Year Factory Service Contract. If the application is not mailedto Mclntosh Laboratory, only the services offered under thestandard 90-day guarantee will apply on this equipment. TAKEADVANTAGE OF 3 YEARS OF FREE FACTORY SERVICE BY FILL-ING IN THE APPLICATION NOW.

In Canada: Manufactured under license by:McCurdy Radio Industries, Ltd.22 Front Street WestToronto, Canada

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LABORATORY INC.

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

Phone-Area Code 607-723-5491

1M-AA107-236 9-15Printed in U.S.A.