McIntosh MR-55A User manual

INSTRUCTIONMANUAL
MclNTOSHMODELMR-55A
AM-FMTUNER
(SerialNo.3K001andup)
McINTOSHLABORATORY,INC.
2ChambersSt.Binghamton,N.Y.
U.S.A.

SPECIFICATIONS:
AM
Sensitivity:
1.5microvolts
Selectivity:
Narrow(4K.C.bandwidth)± 10K.C.fromcenter
down53D.B.
Medium(13K.C.bandwidth)± 10K.C.fromcenter
down20D.B.
Broad(20K.C.bandwidth)
(MeasurementsincludeR.F.andI.F.circuits.Thechar-
acteristicsaresubstantiallyunchangedoverentireR.F.
tuningrange.)
Bandwidth:
I.F.at600K.C.andat1600K.C;20K.C.
R.F.at600K.C.21K.C.;at1600K.C.;23K.C.
AudioBandwidth:
BroadPosition± 3 D.B.;20to9.5K.C.
MediumPosition± 3 D.B.;20to6.5K.C.
NarrowPosition± 3 D.B.;20to2.0K.C.
SensitivitySelector:
ThreePositions
WhistleFilter:
70D.B.rejection10K.C.
Dimensions:
4¾"highx 14¾"widex 12"deep
FM
UsableSensitivity:
3Microvoltsat100%modulation(±75K.C.
Dev.)forlessthan3%totalnoiseanddistortion
I.H.F.M.standards.
CaptureRatio:
1to0.8
I.F.Bandwidth
200K.C.;FlatonTop
I.F.Transformers:
Mechanicallycaptive
Limiters:
Two
LimiterandDetectorBandwidth:
2Megacycles
FrequencyResponse:
±3 D.B.;20-20,000cycles
A.F.C.:
Separatedetector;strong,distortionfree,com-
pletelyvariable
Drift:
±30K.C.withoutA.F.C;negligiblewithA.F.C
AntennaInputImpedance:
300ohmbalanced;75ohmunbalanced
V1—6BK7F.M.R.F.Amplifier
V2—6AB4F.M.Mixer
V3—6BA61stI.F.Amplifier
V4—6AU62ndI.F.Amplifier
V5—6AU63rdI.F.Amplifier
V6—6AU61stLimiter
V7—6AL5A.M.Det.andA.V.C
V8—6AU62ndLimiter
V9—6BN8A.F.C.Detector
V10—6U8F.M.OscillatorandReactor
V11—6BN8SquelchAmplifierandDetector
V12—6AB4 1stAudio
V13—12AU7AudioOutput& F.M.Meter
V14—6BA6A.M.R.F.
VI5—6BE6A.M.OscillatorandConverter
V16—6BW4Rectifier
Dl—IN542Detector
D21847PilotLights(4)
SIZE:
4¾InchesHighx 14¾InchesWidex 12InchesDeep
WEIGHT:
TunerOnly:17Pounds,3 Ounces;InShippingCarton:28Pounds
TUBECOMPLEMENT:
—2—

INSTALLATIONINSTRUCTIONSFORTHE
McINTOSHMR-55AAM-FMTUNER
TheMcIntoshMR-55Aisa superiorqualityAM-FMTunerforuseinhomemusicsystemsandprofes-
sionalapplicationswheredistortionfreereceptionisneeded.Typicalprofessionalusesare"offtheair"re-
cording,broadcastmonitor,rebroadcasting,etc.
Athoroughperusalofthisinstructionmanualwillgivegreaterenjoymentandbetterlistening.TheMR-55A
isthefinesttuneravailableandcompletefamiliaritywithitsfunctionsandoperationwillresultintheout-
standingperformanceyouexpectfroma McIntoshproduct.
TheMR-55Amaybemountedinitsowncabinetorshelfmountedina customcabinet.Thetunerhasbeen
designedtomountona shelfratherthanhangfromthecasttunerpanel.Rubbershockmountingfeethave
beenprovidedtooffertheoptimuminmechanicalisolationfromextraneousvibrations.
Enclosedintheinstructionmanualenvelopearetwocopiesofthe"TUNERPANELCUTOUTTEM-
PLATE"andtwocopies ofthe"SHELFMOUNTINGTEMPLATE"formountingtheMR-55A.Preparethe
cabinetforthemountingoftheMR-55Abyfirstcuttingthewoodencabinetpaneltoreceivethecasttuner
panel.
1.Onthebackofthewoodencabinetpanelmakea verticalcenterlineontheexactcenterofthearea
inwhichthetunerwillmount.Extendthiscenterlinetotheshelf.
2.Foldthe"TUNERPANELCUTOUTTEMPLATE"onthe"FOLDLINE."The"FOLDLINE"is
thelineofthetopoftheshelfonwhichthetunerwillmount.
3.Placethe"TUNERPANELCUTOUTTEMPLATE"intheproperlocationontheinsideofthecabi-
netwiththefoldlineagainsttheshelf.Thetemplatecenterlineshouldmatchthecenterlinescribedon
thepanelinstep1.
4.Inthecenterofthe"CutoutArea"onthe"TunerCutoutTemplate"aretwoholesmarked"LOCA-
TIONHOLES."Carefullyandaccuratelydrillthesetwoholeswitha 5/32inchdrill.
5.Transferthe"TUNERPANELCUTOUTTEMPLATE"tothefrontofthewoodencabinetpanel.
Matchthe"LOCATIONHOLES"fortheproperpositioningofthetemplate.Proceedwithmarkingthelo-
cationofthesixholesandtheoutlineofthecutoutonthefrontofthewoodencabinetpanel.
IMPORTANT:DRILLTHEFOUR3/16INCHANDTHETWO5/32INCHHOLESBEFORE
CUTTINGOUTTHETUNERPANELHOLE.
Thecasttunerpanelhasa 1/4inchoverlaptocovertheedgesofthecutoutincabinetpanel.
Nextpreparetheshelfformountingthetuner.
1.Measurethethicknessofthewoodencabinetpanel.
2."FOLDLINES"havebeensuppliedonthe"SHELFCUTOUTTEMPLATE"forstandardpanel
thicknessuptooneinch.Foldoncorrectfoldlineforyourwoodenpanelthickness.
3.Placethefoldededgeofthetemplateagainstthebackofthefrontpanel.Thetemplatecenterline
mustmatchthecenterlineextendedtotheshelfinstep#1ofthefrontpanelcutoutinstructions..
4.Carefullymarkthelocationsofthefour1/4inchholesandthe8 by101/4inchesventillationhole.
5.Drillandcutouttheshelf.
NextpreparetheMR-55Aformountinginthecabinetbyremovingthepressedwoodshippingpalletfrom
thebottomofthetuner.
Removetheknobsbygentlypullingthemtowardyou.Removethefeltwashers.
Thecasttunerpanelhasbeenattachedtothetunerbytwoanglebracketsthatareforshippingpur-
posesonly.Theseareremovedbyunscrewingthefourscrews(twooneachside)thatholdtheanglebrackets
tothetunerchassis.(SeeFig.1.)Afterremovingthesefourscrewsthetunerpanelcanbeslippedoffover
theknobshafts.
Afterremovingthetunerpanellayitfacedownona protectedsurfaceforthefollowingoperations.
Removethefour6/32screws(oneoneachcorner)thatholdthetwoshippingbracketstothetunerpanel.
—3—

FIG1!
Inthepartsbagaresix6/32x 1 1/4inchesthreadedrods.Installtheseinthesixdrilledandtappedholes
inthebackofthetunerpanel.(SeeFig.2.)
Thetunerpanelisnowreadytobeattachedtothecabinet.Thesixthreaded-rodsareinsertedthrough
thetwo5/32inchandthefour3/16inchholesinthecabinetpanel.Securethetunerpaneltothecabinet
panelbyinstallingontherodsthe6/32"KEP"nutssuppliedinthepartsbag.Bringthenutsuptightwitha
wrenchornutdriver.
Thetuner cannowbeinstalledinthecabinet.Thetunerissecuredtothecabinetshelfbytheinsertion
ofthefour10/32x3/4inchscrewssuppliedinthepartsbagthroughthe1/4inchholesintheshelf.
IMPORTANT:MAKESURETHATTHEINNERCHASSISFLOATSONTHERUBBERSHOCK
MOUNTINGFEET,ANDDOESNOTCONTACTTHECABINETORTUNERPANEL.
Nextreplacethefeltwashersandknobs.
Adequateventilationisessentialtothestableoperationofanytuner.Donotputa solidbackonthe
cabinetbehindthetuner.Ifthetunerismountedverticallymakesuresufficientventilationissupplied.
InstallationintheL-55cabinetisdonebythesameprocedureasforinstallationina customcabinet.
Thecabinetsaresuppliedwiththecutoutsandholesallprepared.
—4—
FIG2

CONNECTINGPROCEDURE
FMANTENNA:Inhighsignalstrengthareasa minimumantenna,suchasthefoldeddipolesupplied,is
allthatisneededforlocalreception.Somecareshouldbeusedinlocatingthefoldeddipoleina positionthat
isfreeaspossiblefromlocalnoisesourcesandshieldingsuchasmetalroofingandbuildingframework.The
dipoleshouldbemountedhorizontally,andat90°tothelineofsightpathtothetransmittingstations.
Infringeareasa goodantennaisrequired.A highlydirectionalbroadbandantennausedinconjunction
witha rotorwillresultinsuperiorperformanceinlowsignalstrengthareas.
AsubstituteforthefoldeddipolecanbeanexistingVHFT.V.antenna.TheMR-55Aissuppliedwith
aninternalswitchingarrangementthateliminatestheneedfortwosetcouplers.TheVHFT.V.antenna
lead-inisconnectedtotheantennaterminalsmarked"FMANT."Connecttheterminalsmarked"TOT.V.
SET"totheantennaterminalsontheT.V.receiverwith300ohmantennaload.(SeeFig.3.)Whenthe
MR-55Aselectorswitchisineitherofthe"FM"positionstheantennaisdisconnectedautomaticallyfromthe
T.V.receiver.InanyotherpositionoftheselectorswitchtheantennaisconnectedtotheT.V.setanddis-
connectedfromthetuner.
75OHMANTENNA:Facilitiesfortheconnectionofa 75ohmantennahavebeenprovidedonthe
backpanel.Connectthecenterconductorofthe75ohmantennaleadtothescrew,ontheFMantenna
terminalstripidentifiedbytheword"ANT"appearingabovethescrew.Theouterconductororbraidedshield
isconnectedtothesheetmetalscrewadjacenttotheantennaterminalboard.(SeeFig.3.1Twolugshave
beenprovidedinthepartsbagtofacilitatetheseconnections.Theimpedanceoftheantennasystemwhencon-
nectedthuslyisa perfect75ohmmatch.
Keepthecenterconductorofthe75ohmleadasshortaspossible.Anyexcessivelengthfromthescrew
terminaltotheplacewheretheshieldbeginswillgreatlydepreciatethesignaltonoiseratio.
A.M.ANTENNA:FacilitiesaresuppliedontheMR-55Afortheuseofa lowimpedanceloopantennaor
ahighimpedancelongwireantenna.AMreceptionwillgenerallybeimprovedthroughtheuseofa properly
installedlongwireoutsideantenna.
Forlocationswhereanoutsideantennaisimpossibleorimpracticala 10footloopantennaissupplied.The
loonisattachedbetweentheterminalsmarked"HI"and"LO"onthe"AM.ANT"terminalstrip.The"AM.
ANT"terminatingswitchmustbeintheloopposition.(SecFig.4.)
Orientationoftheloopiscritical.Itshouldbemountedinaslargea circleaspracticalinthevertical
plane.
FIG3 FIG4
—5—

AnoutsideAMantennaisa wireaslongaspractical,mountedashighaspossibleabovetheground,at
rightanglestopowerlines.TheleadinshouldbecarefullypositionedawayfromallA.C,lines.
The"ANTENNA"terminatingswitchmustbein"ANT"positionwhenusingtheoutsideorlongwire
antenna.
AgoodgroundcanbeofassistanceinAMreception.A goodgroundisdescribedasa 1/2inchrod6 to8
feetlongdrivenintotheearth.Thegroundwireisconnectedtotheterminalmarked"LO."
Ifthetunerisconnectedtoanoutsidegroundasdescribedabovedonotconnectanyoftheotherequip-
menttothesamegroundtopreventgroundloops.Groundloopscancauseanincreaseinhum.
Foranalternategroundforusewhenusinga longwireantennaconnecttheshortinglinkbetweentermi-
nalsmarked"LO"and"GND."(SeeFig.5.)
OUTPUT:Twopinjacksaresuppliedonthebackpanelmarked"Outputs."Thesejacksareinparallel.
Theoutputisunbalancedlowimpedance.Interconnectbetweeneitherofthesejacksandthetunerinputof
yourpreamplifierbymeansofthe6 footshieldedcablesuppliedwithyourtuner.
PlugtheA.C.cablefromthetunerintooneoftheauxiliaryA.C.outletsonthebackofthepreampli-
fier.
-6-

MultiplexOutput
TheoutputonthebackoftheMR-55Amarked"MULTIPLEXOUTPUT"isanunfilteredoutputfor
feedinga multiplexadapter.
OPERATION
InputSelector
Theinputselectorhassixpositionsidentifiedas(1)PHONO,(2)A.M.SHARP,(3)A.M.MED,
(4)A.M.BRD,(5)F.M.TUNE,and(6)F.M.LISTEN.
A.M.
AstheaudioresponseisincreasedonA.M.theambient,manmadenoisesinA.M.receptionarein-
creased.Wideaudiobandwidthmaygivesuperiorresultsonstronglocalstationsandproveunlistenableon
distantstations.ToincreaseenjoymentofdistancereceptiontheaudiobandwidthofyourMR-55Ahas
beenlimitedbymeansoftheinputselectorswitch.Theselimitsareonthreepositions:A.M.Sharp,A.M.
Medium,andA.M.Broad.
A.M.Sharp
Theaudioresponseofthispositionislimitedto20cyclesto2000cycles.Inthe"A.M.SHARP"position
distantstationscanbereceivedwithmaximumclarityandminimumnoise.Tunetoa peakonthesignal
strengthorleftmeter.TherightmeterorcenterofchannelmeterisonlyinuseonF.M.
A.M.Med.
TheaudioresponseoftheA.M.MKD.positionislimitedto20cyclesto6500cycles.Thispositionis
lessselectiveonnoisethanthe"SHARP"position.
A.M.Brd.
Theunrestrictedaudioresponseis20to10,000cyclesformaximumA.M.fidelityonstronglocalsta-
tionswherenoiseisnota problem.Tunetoeithera peakonthesignalstrengthmeter,ortotheloudest
sound.
WhistleFilter
InallA.M.positionsthereisa 70DBrejectionofthe10KCwhistle.
F.M.Tune
Automaticfrequencycontrol(A.F.C.)isdisabledandULTRASONICMUTINGisaddedformaxi-
mumaccuracyandease intuning.Ultrasonicmutingeliminatestheannoyingnoisebetweenstations.Intun-
ingacrossthebandtakenoticeofthecompleteabsenceofnoiseevenwhenapproachinga station.
Somestationsarereceivedwithinsufficientsignalstrengthtocompletelyeliminatebackgroundnoise.The
ultrasonicmutingcircuithasbeensodesignedtopermitonlylistenablesignalsthrough.Signalswithannoy-
ingbackgroundnoisewillbemuted.Themeterswillfunctionnormallyandindicatethepresenceofa sta-
tion.Ifa desiredstationisnotheard,tunebymeterandchangetheselectorswitchto"F.M.LISTEN."The
stationcanthenbeheard.UltrasonicmutingisanexclusiveMcIntoshdevelopmentandfeature.
Ifanantennawitha rotorisusedthesignalstrengthmetercanbeofassistanceindeterminingthe
properdirectiontopointtheantenna.Rotatetheantennauntilmaximumsignalstrengthisregisteredonthe
meter.Thebestsignaltonoiseratiousuallywillresultathighestindicatedsignalstrength.
Muting
McIntoshdesignedUltrasonicmutingisanexclusiveinyourMR-55A.Thethresholdofmutingisad-
justable.Thecontrolshaftmarked"R73"onthetopleftrear,asyoufacethefrontofthetuner,isthemuting
adjustment.
Themutinghasbeensetduringfinaltestforanybroadcastsignalsthatmaybenoisyinreception.If
lessmutingiswantedadjustthecontrolsasfollows:
1.Turntheinputselectorto"FMLISTEN."
2.Tunetothenoisebetweenstations.
3.Turntheinputselectorto"FMTUNE."
4.Adjustthe"R73"untilthenoiseisheard,thenbackoffuntilthenoisejustdisappears.
Adjustmentbythismethodresultsinthegreatestnumberofstationswithminimumbetweenstationnoise.
—7—

F.M.Listen
TheultrasonicmutingcircuitisdefeatedandA.F.C.addedforgreatestlisteningpleasure.McIntosh
A.F.C.doesnotchangeinanyrespectthelowdistortioncharacteristicsoftheMR-55A.
Volume
Thevolumecontrolhasatitsextremecounter-clockwiserotationtheA.C.on-offswitch.Theswitch
alsocontrolstheA.C.availableattheauxiliaryA.C.outletonthebackofthetuner.Normaloperationfor
the "VOLUME"controlistotallyclockwise.
A.M.Sensitivity
TheA.M.sensitivityisthegreatestattheclockwisepositionoftheswitch,thecenterpositionisinter-
mediatesensitivity,andthecounter-clockwisepositionisminimumsensitivity.
Theclockwiseormaximumsensitivitypositionwilldeliverthegreatestnumberofstations.Longdistant
receptionwillbebestinthisposition.Whenselectinglocalstationsbetweenstationnoisecanbereducedby
usingeithertheminimumorintermediatesensitivitypositionswhicheverismostsatisfactoryforyourlocation.
A.F.C.
Thecontrolidentifiedas"F.M.-A.F.C."islocatedattheextremeleftofthefrontpanel.A.F.C.means
automaticfrequencycontrol.Itspurposeistolockandholda stationwhenlisteningtoF.M.Theamountof
A.F.C.usedisvariablefromnoneinthecounterclockwiserotationtofulloninthecounter-clockwiserota-
tion.
TheamountofA.F.C.usedcanbevariedwithconditions.Ifa weakerstationisadjacenttoa strong
station,toomuchA.F.C willcausethestrongstationtocomeinandcompletelyblocktheweakerstation.
ByreducingtheamountofA.F.C.(rotatingthecontrolcounter-clockwise)theweakerstationwillbelocked
andheld.
McIntoshA.F.C.isexceedinglystrong.DuetotheincomparableMcIntoshdesigntheexcellentaudio
qualitywillnotbeadverselyeffectedovertheentirerotationoftheA.F.C.control.
Dial
InadditiontotheregularA.M.andF.M.identificationonthediala loggingscalehasbeensupplied
tofacilitaterepeattuningoffamiliarstations.
SERVICEINFORMATION
AllMcIntoshequipmentisdesignedforlongtroublefreeoperation.Allcomponentsareofhighestqual-
ityandareconservativelyoperated.Iftroubledevelopstheequipmentmaybeservicedbyyourfranchised
dealer,a competentserviceman,orreturnedtothefactory.Equipmentwillnotbeacceptedatthefactory
unlessfactoryreturnauthorizationisfirstreceived.
Muchresearchhasbeendoneinourlaboratorytoovercometheneedforalignmentandadjustmenten-
counteredinhighqualitytuners.Designparametershavebeenselectedsothatmajorchangescanoccurin
componentswithoutdegradingthehighqualityresults.Tubereplacementsseldomrequirere-alignment.Trans-
formershavebeenmademechanicallycaptivetopreventmisalignmentduetovibrationandshock.There-
fore,theneedforadjustmentandalignmenthasbeensubstantiallyreduced.McIntoshLaboratory,ofcourse,
willalignandadjustanytuneruponrequest.
GUARANTEE
Weguaranteetheperformanceofthisequipmentandthemechanicalandelectricalworkmanshiptobe
freeofseriousdefectsfora periodof90days.Thisguaranteedoesnotextendtocomponentsdamagedbyim-
properusenordoesitextendtotransportationtoandfromthefactory.
McINTOSHLABORATORY,INC
2ChambersStreet
Binghamton,N,Y.,U.S.A.,
InCanada:ManufacturedUnderLicensebyMcCurdyRadioIndustries,Ltd.
22FrontStreetWest,Toronto,Canada
—8—
BE112003