McIntosh MR 73 User manual

SOLIDSTATE
FM-AMTUNER
STEREO
MR73
PRICE$1.26

TheMclntosh"willtoperfection"requiresthatweprobe
constantlyintotheunknowntobringtheperformanceofour
electronicequipmentclosertoperfectionthaneverbefore.
Thisrequiresa constantandrelentlesssearchforlownoise,
broadbandconservativedesignwithaneverlowerdistortion
factor.Thisisnotrequiredofordinaryequipmentofaverage
designs.Itis,forus,a costlybutworthwhilescientificand
engineeringeffort.Ourcontinuingresearchbenefitsourcus-
tomerswiththealmostcompletelackofobsolescenceand
themostreliableequipmentevermade.Italsomeansthe
lowestlong-rangecosttoyou.NearlyalloftheMclntosh
equipmentevermadeisstillinuse,oruseable,thoughit
mayhavebeenmadetwentyyearsago.
CONTENTS
INTRODUCTION2
TECHNICALDESCRIPTION2-4
IFYOU'REINA HURRY5
PERFORMANCECHARTS6
SPECIFICATIONS7
INSTALLATION8-9
FRONTPANELINFORMATION10-11
BACKPANELINFORMATION12
TYPICALHOOKUP13
CONNECTING14
LISTENING15
GUARANTEE16
Yourpurchaseofa Mclntoshinstrument
showsthatyouarea carefuldiscriminat-
ingbuyer.Onewhoisinterestedinquality
performance,qualityengineering,quality
manufacturing,andlongtrouble-free
equipmentlife.Youcanprotectyourin-
vestmentbyspendinga fewminutesread-
ingthisowner'smanual.
Whenyouboughta Mclntosh,youbought
countlesshoursofmusicalpleasureand
superiorperformance.Enjoyit!
SOLIDSTATE
FM-AMTUNER
STEREO
MR73
1

INTRODUCTION
TheMclntoshMR73isa precisionengineered,highlysensitive
solidstateAM-FMtuner.
TheresearchstaffofMclntoshLaboratory,usingthelatesttech-
nologyinsolidstatephysics,hasdevelopedmanycircuitadvances:
-PhaselinearcrystalshapedIFamplifiers
-IntegratedCircuitsthataretheequivalentof16transistors,
3zenerdiodes,5 diodes,and23resistors
-Specialmultiplex(stereo)detectingcircuitsthateliminate
criticaladjustments
-Ultrasonicmutingforcompletesilencebetweenstationswhile
tuning
-Automaticstereo-monoswitchingthatis"clickless"andcom-
pletelyelectronic
-Visualmultipathindicatortohelpavoidmultipathdistortion
showingasa visualindicatorofcorrectantennadirectionfor
minimummultipathreception.
-NewD'Arsonvalmovementmetersofincreasedsensitivity
whichdonotneedzerosettingadjustments.
-A newcomputerdesignedfiltertoreducenoisefromstations
broadcastingsubcarrierauxiliarymusicservices.Noother
tunerusessucha filter.
ExclusiveMclntoshPANLOCisusedforinstallation.ThePANLOC
systemgivesyouabsoluteeaseofinstallation,operation,andmain-
tenance.
PANLOCisthefirstprofessionalinstallationtechniquetobeused
onstereoinstruments.
InthePANLOCsystema metalshelfismountedfirst.Thetuner
slidesintopositiononthisshelf.DepressingthefrontpanelPAN-
LOCbuttons,locksthetunerfirmlyintopositionagainstthemount-
ingpanel.
Onceyouhaveenjoyedtheoutstandingperformanceofthe
MR73,youwillunderstandwhyMclntoshproductshaveearned
theirreputationas"THEBEST."YourMclntoshMR73tunerwill
giveyouyearsofthefinestpossiblereception,andwillbea valued
partofyourhomemusicsystem.
2
TECHNICALDESCRIPTION
F.M.SECTION:Thisisdividedintotwoseparatemodularsections:
A.The100mHzRadioFrequency{RF)Section.Thissection
housesthecompleteFM-RFfront-endandpartoftheAM-RFcir-
cuits.A special,foursection,variabletuningcapacitorprovidesa
highdegreeofRFselectivityandexcellentspuriousresponserejec-
tion.Theproblemofimagerejectionhasbeengreatlyreducedinthe
RFsectionoftheMR73.
Thetwostageparallel-fed-cascodejunctionfieldeffecttransistor
(JFET)RFamplifiergivesbettersensitivityandhighergainthan
conventionalone-stageamplifiers.TheuseofJFET'shelpstofurther
reducetheproblemoffrontendoverloadinstrongsignalareas.
Amixerusinga JFEThasbeendesignedforhighsensitivityand
freedomfromoverload.Lowtemperaturecoefficientcomponents
havebeendesignedintotheFMlocaloscillatortopreventfre-
quencydrift.Thefrequencystabilityinherentinthelocaloscillator
makesautomaticfrequencycontrol(AFC)unnecessary.Therateof
driftofthelocaloscillatorislessthantenpartspermillionper
degreecentigrade.
BoththeFMandAM-RFfrontendshavebeendesignedinthe
samecompletelyencasedmetalmodules.Thisdesigngivesprotec-
tionagainstradiationorinterference.TheRFcircuitsoftheMR73
exceedtheFCCrequirementsforsuppressionofoscillatorradia-
tion.
TheMR73hasantennaconnectionsforeither300ohmtwinlead
transmissionlineor75ohmcoaxialcable.Thenormalinputim-
pedanceofthefirstRFamplifieris75ohms.Impedancematchto
300ohmsisprovidedbya Mclntoshdesignedbaluntransformer
whichhasnegligiblelosses.Connectionsfora 300ohmlineare
madewithnewpushtypeterminals.Notoolsarerequired.A typeF
maleconnectorisfurnishedfor75ohmcoaxialcable.
Forgreatersignaltransferandlowerdistortion,a specialmatch-
ingtransformerhasbeendesignedtointerfacetheFM-RFtothe
FM-IFamplifier.Thismatchingtransformerconsiderablyenhances
thelinearphasecharacteristicsoftheIFamplifier.
B.TheFM-IFandDetectorSection.TheFM-IFandDetectorde-
signrequiredextendedengineeringtimeandtestingandusesthe
latestconceptsinintegratedcircuitsandcrystalfilters.TheFM-IF
consistsoftwointegratedcircuitsandtwophaselinearcrystal
filters.Theycombinetogivea totalgainofover120dB(thesignal
isamplifiedtoover1,000,000timesitsoriginallevel).Theresponse

curvehasa nearlyflattopwithlinearphasecharacteristics.The
skirtsoftheresponsecurveareverysteep.Themaximumwidthis
240kHzat-3.0dBand400kHzat-60dB.Theresponsecurveis
symmetricaleachsideofthecenterfrequency.Thecrystalfiltersare
permanentlysealedanddonotrequireadjusting.TheIFcannot
driftnorvibrateoutofadjustment.
EachofthetwointegratedcircuitsusedintheFM-IFoftheMR73
contain16transistors,3 zenerdiodes,5 diodesand23resistors,all
ona singlemonolithicsiliconchip.
Theexceptionallyhighgainofthetwointegratedcircuitsassumes
"hardlimiting"atverylowlevelsofinputsignals.
A"phase"or"FosterSeeley"discriminatorhasbeendesigned
tocomplementtheintegratedcircuitIFsection.TheIFsectionhas
exceptionallyhighgainandhardlimitingcharacteristics,yetthe
captureratioisquitelow.Thedetectedoutputsignalofthedis-
criminatorisextremelylowindistortioncontent.
De-emphasisofthediscriminatoroutputrestoresthefrequency
amplitudecharacteristicstothesameleveltheywerebeforetrans-
mission.
C.FMStereoMultiplexSection.MclntoshLaboratoryhasde-
velopeda specialdetectingcircuitinthemultiplexsection.A par-
ticularadvantageofthiscircuitistheeliminationofthecritical
adjustmentsnecessarywithcommonlyusedmatrixingcircuits.The
circuitdetectstheL-Rsidebands,thenautomaticallymatrixesthe
recoveredinformationwiththeL + R maincarriersignal.Thisyields
theleftandrightprogramoutputwithmaximumseparation.
The19kHzpilotsignalisfilteredfromthecompositestereoinput
signal,amplifiedbya speciallimitingamplifier,doubledtothe38kHz
carrierfrequency,andthenamplifiedagainbya limitingamplifier.
Thecompositesignalminusthe19kHzpilotiscombinedwiththe
38kHzcarriersignal.Thenewcombinationofsignalsisfedtothe
specialdetectorcircuitmentionedabove.Balancedfullwavede-
tectorsareusedtocancelthe38kHzcomponentsintheoutput.
TheSCA(SubsidiaryCommunicationAuthorization)signalmust
beremovedfromthecompositeoutput.Thisisaccomplishedbythe
useofa new"ImageParameter"bandeliminationfilterthathas
beencomputerdesigned.TheSCAfilterrejectsSCAsignalswithout
impairingstereoperformance.
FMmutingintheMR73operatesbydetectingultra-sonicnoise
whichispresentwhentuningbetweenstationsorwhenreceiving
aweakstation.Themutingcircuitcanbeactivatedordefeatedby
theuseofthemutingswitchonthefrontpanel.Thelevelofmuting
desiredcanbeadjustedbythemutinglevelcontrolonthetoppanel.
Varyingthemutingcontroladjuststhethresholdatwhichthemuting
takeseffect.
Whenthe19kHzcarrierofa stereosignalisreceived,theauto-
maticFMstereoswitchingcircuitactivatesthemultiplexdecoding
circuit.Thislightsthestereoindicator.Thecircuitswitchingisall
doneelectronicallywithnoclicks.Theautomaticstereoswitching
canbedefeatedbyturningthemodeselectorswitchtoFMMONO.
(Inthispositionthestereoindicatorwillstilllighttoindicatethe
presenceofa stereosignal.)Onmonophonictransmissionsthe
stereoswitchingisinactiveatalltimes,assuringa greatersignalto
noiseratio.Thestereoswitchingcircuithasbeendesignedsothat
noisewillnotactivateit.
AMSECTION:
The"stateoftheart"inelectronictechnologyhasbeenincorpo-
ratedbyMclntoshintotheMR73withtheuseofmetaloxidesilicon
fieldeffecttransistors(MOSFET's)intheAMsection.AnAM-RF
amplifiercircuitincludesa threesectionvariabletuningcapacitor
inthemetalenclosedshieldedmodule,whichalsohousesthe
FM-RFfrontend.TheAM-RFamplifierusesa dual-insulatedgate
MOSFETtoobtainmoreoverloadprotectionagainststronglocal
stationsthancanbeobtainedwithconventionalbipolartransistors.
TheAM-RFmixerisalsoa dual-insulatedgateMOSFET.Theuse
ofMOSFET'sintheRFamplifierandmixerprovidestheMR73with
verylittlecrossmodulation(spuriousresponse)andtheimagere-
jectionisverygood.
ThreedoubletunedIFtransformersareusedtoobtaina high
degreeofselectivityyetstillallowgoodAMfidelity.A 10kHzwhistle
filterhasbeenincorporatedattheoutputoftheAMdetector.Its
3

purposeistosupresshetrodyningthatoccursbetweenadjacent
AMcarriers.
Toincreasethe"pullingpower"oftheAMsectionoftheMR73,
connectanexternalantennaattherearapronoftheunitbyusing
apushconnector.Aninternaltransformermatchestheexternalan-
tennatotheinputimpedanceoftheAMfrontend.Anoptionalhighly
sensitiveloopstickantennaisalsoprovidedforlocalorstrong
stations.A switchonthebackpane!selectseitherloopstickor
externalantenna.
AnAMsensitivityswitchhasbeenprovidedtodecreaseboththe
gainoftheRFamplifierandthenoisebetweenstations.
AUDIOPREAMPLIFIERSECTION:
AnaudioamplifierhasbeenincorporatedintheMR73.Itin-
creasestheaudiolevelfromtheAMorFMmultiplexoutputstoa
levelsufficienttodrivea preamplifierorotheraccessoryequipment.
Theaudioamplifierconsistsof2 separateamplifiers,eachamplifier
havingthreetransistors.Thedesignusesconsiderablenegative
feedback.Negativefeedbackhelpstoachievelowdistortion,wide
frequencyresponse,andunexcelledstability.Eachaudioamplifier
hastwolowimpedanceoutputs.Oneisa fixedoutputsetat2.5
volts.Thesecondoutputisvariablebythevolumecontrolonthe
frontpanel.
Bycross-couplinga smallportionofonechannelintotheother
intheaudioamplifier,theresidualalternatechannelinformation
canbecancelled,therebyfurtherincreasingthestereochannel
separation.
Alsoincludedintheaudiosectionisa STEREOFILTERswitch.
WiththeSTEREOFILTERturnedonandweakstationsarebeing
received,stereonoiseisreduced,butstillallowsamplestereo
listeningperformance.
POWERSUPPLY
Specialdesignattentionhasbeengiventothepowersupply
sectionoftheMR73.Twoseparaterectifiercircuitsareusedin
theMR73.
The16voltregulatoristhepowerheartoftheMR73.Allsignal
stagesthroughouttheunitarepoweredfromthisregulator.The
16voltregulatorisveryelaborateindesign,usinga speciallyse-
lectedtransistorandassociatedcircuit.Theregulatoruseselec-
tronicfilteringtoinsurethelowestpossiblebackgroundhumlevel,
maximumstabilityandextremelygoodregulation.
Ahalfwaverectifierandfilter,supplytheDChighvoltageneeded
fortheanodeofthemultipathindicator.Thesecondpowersupply
isa fullwaverectifierwhichsuppliesDCtothemultiplexindicator
andtothevoltageregulator.
4

IFYOU'REINA HURRY
MODESELECTOR—SelectfromAMbroadcast,stereoFMbroadcast,or
monoFMwithoutautomaticstereo/monoswitching.
STEREOFILTER—ReducesnoiseonweakFMstereobroadcasts.
MUTING—EliminatestheusualnoisebetweenFMstations.
VOLUME/OFF—TurnstheACtothetuneronoroffandadjustsvolumeto
desiredlevel.
STEREOINDICATOR—Lightswhenstationistransmitting19kHzcarrier
forstereobroadcast.
MULTIPATHINDICATOR—Rotateantennauntilelectronrayedgesare
steady.
SIGNALSTRENGTH—Tuneformaximumreadingwitha steadymultipath
indicator.
FMTUNING—TuneFMuntiltheindicatorisintheblackareainthecenter
ofthemeterface.
5

FMSTATIONLOG
STATIONDIAL
FREQ.
LOG
SCALELOCATION CITY,STATE
ANTENNA
DIRECTIONREMARKS MONO—STEREO-TIME-DATE
6

SPECIFICATIONS
FM
USEABLESENSITIVITY:2.5microvoltsat100%
modulation(±75kHzdeviation)forlessthan3%
totalnoiseandharmonicdistortioninaccordance
withIHFstandards.
AUDIOFREQUENCYRESPONSE:Flatfrom20Hz
to20kHZwithstandardde-emphasisand19kHz
pilotfilter.
HARMONICDISTORTION:Mono:Lessthan0.3%at
100%modulation±75kHzdeviation.Stereo:Less
than0.7%.
CAPTURERATIO:Betterthan1.5%dBat100%
modulation.
MUTING:AFinjectedultrasonicmuting:atleast
60dBnoisereductionbetweenstations.
OSCILLATORDRIFT:Lessthan25kHz.
IMAGEREJECTION:Betterthan80dBat90MHz;
betterthan70dBat100MHz.
HUM:Betterthan70dBbelow100%modulation.
OUTPUT:Approximately2.5volts;lowimpendance.
FMANTENNAINPUTS:300ohmsbalanced;75ohms
unbalanced.
AMANTENNAINPUTS:Built-inloopstickorexternal
antennaswitchselected.
IF:TwoICsandtwophaselinearcrystanfilters.
RADIATION:SubstantiallybelowFCCrequirements.
STEREOSEPARATION:Betterthan35dBat1 kHz.
STEREOFILTER:Greaterthan48dBsuppressionof
38kHzmultiplexcarrier.
STEREOINDICATOR:Frontpanelmultiplexstereo
lightactivatedby19kHzcarrier-only.
SCAFILTER:50dBdownat67kHzto74kHz,275
dBperoctaveslope.
AUTOMATICMONO-STEREOSWITCH:Mclntoshde-
veloped;allelectronicautomaticmono-stereoswitch-
ingcircuit.
SEMICONDUCTORCOMPLEMENT:22diodes,24
Transistors,2 IntegratedCircuits,1 IndicatorTube.
AM
SENSITIVITY:Betterthan12microvoltsat1000kHz
(usingtheexternalantennainput).
FREQUENCYRESPONSE:Down6 dBat5 kHz.
HARMONICDISTORTION:Lessthan1%at30%
modulation.
SELECTIVITY:-30dBat10kHz.
IMAGEREJECTION:60dBorgreaterat1000kHz.
SIGNALTONOISERATIO:Betterthan55dB.
POWERCONSUMPTION:20watts,105to125volts,
50to60Hz.
MECHANICALSPECIFICATIONS
SIZE:Frontpanel:16incheswideby5 7/16inches
high;Chassis:15incheswideby13inchesdeep,
includingPANLOCshelfandbackpanelconnectors;
KnobClearance:1½inchesinfrontofmounting
panel.
WEIGHT:24poundsnet,36poundsinshipping
carton.
FINISH:Frontpanel:Anodizedgoldandblackwith
specialgold/tealpanelnomenclatureillumination.
CHASSIS:Chromeandblack.
MOUNTING:Mclntoshdevelopedprofessional
PANLOC.7

INSTALLATION
Adequateventilationextendsthetrouble-freelifeofelectronicin-
struments.Itisgenerallyfoundthateach10°centigrade(18°F)rise
intemperaturereducesthelifeofelectricalinsulationbyonehalf.
Adequateventilationisaninexpensiveandeffectivemeansofpre-
ventinginsulationbreakdownthatresultsfromunnecessarilyhigh
operatingtemperatures.Thedirectbenefitofadequateventilation
islonger,trouble-freelife.
ThesuggestedminimumspaceformountingtheMR73is15
inchesdeepx 17%incheswidex 16incheshigh.Alwaysallowfor
airflowbyeitherventilationholesorspacenexttothebottomof
theamplifieranda meansforthewarmairtoescapeatthetop.
ItisrecommendedthattheMR73bemountedina normalorhori-
zontalposition.However,withadequateventilationtheamplifiercan
bemountedinanyposition.
TopreparetheMR73forinstallationremovetheplasticprotective
covering.TurntheMR73upsidedownsothatitrestsonitstopon
theshippingpallet.Removethefourplasticfeetfastenedtothe
bottomofthechassis.
Nextplacethemountingbrackets,thepartsbagandthemounting
templateforeasyaccessibility.
Theprofessionalmountingdesigneliminatestheneedforany
shelforbrackettosup-
porttheMR73.Itis
completelysupported
byitsownmounting
brackets.
Positiontheplastic
mountingtemplate
overtheareaofthe
paneltobecutoutfor
installation.
Thedesignofthemountingtemplateallowsyoutopositionor
locatethecutoutfromthefrontorrearofthepaneltowhichthe
instrumentistobemounted.
Ifthecutoutistobelocatedfromtherearofthepanel,the
followingstepswillhelpyou.
Onthebackofthecabinetpanel,scribea verticalcenterline
throughtheexactcenteroftheareainwhichthecutoutisto
bemade.
Placethetemplateagainstthebackofthepanelandmatch
thetemplatecenterlinewiththecenterlineonthecabinetpanel.
Makesurethatthereisatleast¼ inchclearancebetweenthe
bottomofthedashedlineofthecutoutareaonthetemplate
andanyshelforbracebelowtheproposedcutout.
Markthetwolocatingholes("C"holesonthemountingtem-
plate).
Drillthetwolocatingholes.Becertainthedrillisperpendicular
tothepanel.
Nowpositionthetemplateonthefrontofthepanelbyaligning
the"C"locatingholesonthetemplatewiththedrillholes.
8

Withthetemplateinplaceagainstthecabinetpanel,markthe
"A"and"B"drillholesandthefoursmallholesthatidentifythe
cornersofthecutout.Jointhecornermarkswitha pencil.Theedge
ofthetemplatecanbeusedasa straightedge.
IMPORTANT:
CUTOUT.DRILLTHE6 HOLESBEFOREMAKINGTHE
Accuratelydrillthethreeholesoneachsideofthecutoutarea
witha3/16inchdrill.
WiththesawontheINSIDEOFTHEPENCILLINEScarefullycut
outtherectangularopening.
Securethemountingstripstotherearofthecabinetpanelusing
twoscrewsfromthehardwarepackage.
Insertthescrewsinthecenterholesofthecabinetpanel("B"
holesonthetemplate)andtighten.Thescrewheadshouldpull
intothewoodslightly.(Usetwo¾ inchlongscrewsforpanelsunder
½inch,ortwo1¼inchlongscrewsforpanels½ inchthickand
larger.)
Attachthemountingbracketstothecabinetpanelusingfour
screws.
Placethetemplateoverthemountingscrews.Themounting
screwsshouldbecenteredinthe"A"and"B"holesonthetem-
plate.Thesidesofthemountingbracketsshouldmatchthevertical
dashlinesonthetemplate.Ifnecessary,loosenthescrewsand
pushthebracketsintoalignmentandretighten.
Insertthepowercordthroughtheopening.Carefullyslidethe
MR73intotheopeningsotherailsonthebottomoftheequipment
slideinthetrackofthemountingbrackets.Continuetoslidethe
instrumentinuntilthefrontpanelisagainstthecabinetpanel.
AtthebottomfrontcornersofthePANLOCinstrumentsarethe
PANLOCbuttons.
DepressingthePANLOCbuttonswilllocktheinstrumentfirmly
intheinstallation.
DepressingthePANLOCbuttonsa secondtime(aswitha ball-
pointpen)willreleasetheinstrument.Youcanthenslidethe
instrumentforwardtotheinspection-adjustmentposition.
Depressingtheinspection-adjustmentpositionlatcheswillallow
theinstrumenttobeslidcompletelyoutoftheinstallation.
VERTICALINSTALLATION
Inthehardwarepacketaretwohelicalsprings.Fasten thesprings
tothesmallflangesattherearofthePANLOCbrackets.Theflange
hasa notchanda holetomountthespring.Thespringsassistinthe
removalofverticallymountedPANLOCequipment.
DONOTUSETHESPRINGSONHORIZONTALLYMOUNTEDEQUIPMENT.9

FRONTPANELINFORMATION
TUNINGDIAL
TheMR73hasthreedialscales:
1.AM—Marked55to160kHz
2.FM—Marked88to108MHz
3.Loggingscale— Marked0 to100
Theloggingscalecanbeusedtoaccuratelyretuneanystation.
Youmayfinditeasiertokeepa recordofyourfavoritestationsby
useoftheloggingscale.
Asmallportionofdialpointerhasbeenilluminatedtoincrease
theeaseoftuning.
INDICATORS
TheMR73hasfourindicatorsonthedialpanel:STEREOindi-
cator,MULTIPATHindicator,SIGNALSTRENGTHmeter,andthe
TUNINGmeter.
STEREOINDICATOR
TheSTEREOindicatorwilllightwhenthedialpointercrossesa
stationbroadcastingthe19kHzcarrierforstereo.Thespecialcir-
cuitusedwilllightonlywhenthe19kHzmultiplexcarrierispresent
inthesignal.Theindicatorwillnotlightonnoisepulsesorinter-
ference.
MULTIPATHINDICATOR
TheMULTIPATHindicatorisanexclusiveMclntoshdevelopment.
TheproperuseoftheMULTIPATHindicatormakesitpossibleto
improveFMreceptionwithpreciseFMantennapositioning.
Anelectronrayindicatorisusedtographicallyshowmultipath
reception.Theelectronrayindicatoroperatesbymovementof
electronbeamsinsidea vacuumtube.Themultipathindicatorshows
whentheantennaisrotatedtothecorrectpositionforpickingup
onlythedesiredsignal.Multipathdistortioncausesthetwobeams
ontheindicatortofluctuaterapidlywiththeincomingsignal.When
theantennaisrotatedtothecorrectposition,theindicatorbeams
willremainsteady.Thedirectionalantennaisthenpickinguponly
thedesiredsignalandrejectingthereflectedmultipathsignals.In
certainlocationsitispossibleforbestreceptiontooccurbypicking
upa strongreflectedsignalratherthanthedirectsignal.Whenever
tunedtoa differentstation,themultipathindicatorwillshowif
multipathdistortionispresent.Multipathdistortionispractically
independentofsignalstrength.
SIGNALSTRENGTHMETER
Thismeterindicatesthestrengthofthereceivedsignalfromthe
antenna.Thehighertheindicationthestrongeristhesignal.
FMTUNINGMETER
AnFMstationiscorrectlytunedwhentheindicatorisintheblack
areaofthetuningindicator.TheactionoftheTUNINGindicatoris
independentofstationsignalstrength.
MODESELECTOR
Selectsanyoneofthreeprogramsources:
AM— ConnectstheAMtunersectionoftheMR73totheoutput
jacks.
FM— TheFMpositionprovidesmonophonicFMorFMstereoat
theleftandrightchannelaudiooutputjacksautomatically.
WiththeMODESELECTORintheFMpositiona station
broadcastingmonophonicprogramwillbeheardinmono.
Whenthestationswitchestostereobroadcast,thestereo
indicatorwilllightandtheMR73willautomaticallyswitch
tostereooperation.Ifmonobroadcastingisresumedthe
MR73willautomaticallyswitchtomono.
FM— Mono— ConnectstheFMtunersectionsoftheMR73to
theoutputjacks.Inthispositiontheautomaticstereo
switchingisbypassed.Thestereoindicatorwilllightwhen
astationistransmittingstereo.Theoutputwillbeonly
mono.
10

STEREOFILTER
TheSTEREOFILTERreducesnoiseonweakstereostations.
TurntheswitchtotheINpositiononnoisystereostations.
FMMUTING
Mutingsuppressesthebackgroundnoiseandhissnormallyheard
betweenstations.TurnthecontroltotheINpositionformuting.
Weakstationsthatmaynotoverridenoiseandinterferencearealso
suppressedbythemuting.
IntheOUTposition,themutingisturnedoff.Thisallowsconven-
tionalFMtuningwiththenoiseandinterferencepresent.Usethis
positiontotuneweakornoisystations.
VOLUME
Thiscontroladjuststheoutputvolumelevelofthetuneratthe
backpanelAUDIOOUTPUTjacksmarkedFRONTPANELCON-
TROLLED.TheotherpairofjacksismarkedFIXEDOUTPUT.They
arenotaffectedbythevolumecontrol.Fulltuneroutputisalways
presentattheFIXEDOUTPUTjacks.
TheVOLUMEcontrolhasbeenprecisiontrackedthroughoutthe
listeningrange(0to—65dB)foraccuratestereobalance.
ACON/OFF
TheACswitchispartoftheVOLUMEcontrol.TurningtheVOL-
UMEcontroltotallycounterclockwiseturnstheACtotheMR73
OFF.
PANLOCBUTTONS
AtthebottomofthefrontcornersarethePANLOCbuttons.After
atunerisinstalledonthePANLOCshelf,depressingthePANLOC
buttonswilllockthetunerfirmlyinposition.DepressingthePAN-
LOCbuttonsa secondtime(aswitha ball-pointpen)willreleasethe
tuner.Thetunercanthenbeslidforwardtotheinspectionand
adjustmentposition.ThePANLOCsystemgivesyouabsoluteease
ofinstallation,operationandmaintenance.
SECONDARYCONTROLS
Onthetopofthechassisbehindthefrontpanelarethreesec-
ondarycontrols.TheyareMUTINGadjust,AMSENSITIVITY,and
DIALSCALEINTENSITY.
MUTING
TheMR73ultrasonicmutingcircuitsuppressesallnoisebetween
stations.Itsuppressesallweakerstationsnotstrongenoughto
overridethebackgroundnoise.
Themutingthresholdsettingdeterminesthestrengthofthesignal
whichcanbeheardwithmutinginoperation.Themutingthreshold
iscarefullyadjustedtooptimumatthefactoryusingprecisiontest
instruments.
Ifitisfoundnecessarytoadjustthemutingthreshold,turnthe
MUTINGADJtotheRIGHT(clockwise)tolowerthemutingthresh-
old.ThisallowsweakernoisierstationstobeheardattheMUTING
INsetting.Turnthecontroltotheleft(counterclockwise)toraisethe
mutingthreshold.Thisallowsonlythemorepowerfulstationstobe
heardattheMUTINGINsetting.
AMSENSITIVITY
WhentheAMSENSITIVITYswitchisintheLOWpositionthe
noisebetweenstationsisreduced.TheRFgainisnotasgreatinthe
lowposition.
DIALSCALEINTENSITY
Adjustthebrightnessofthedialpanellightsbymeansofthis
switchonthetunerbackpanel.SettheswitchtoBRIGHTfor
maximumpanellight.SettheswitchtoDIMforlessdiallightand
extendedlamplife.
11

BACKPANELINFORMATION
TP1andTP2
TestpointTP1andTP2isprovidedfortunercircuitalignment.
ItisalsousedinconjunctionwiththeMclntoshMl3,MaximumPer-
formanceIndicator.
ACOUTLET
Provides117voltACpowerupto350wattsforadditionalequip-
mentsuchasturntables,orotherequipment.Thisoutletisnotfused.
ItturnsonandoffwiththefrontpanelACswitchontheVOLUME
control.
AUDIOOUTPUTS
Theleft-handpairofAUDIOOUTPUTjacksprovidesaudiosignals
unaffectedbytheMR73frontpanel VOLUMEcontrol.Usethese
outputjackstoconnectthetunertoa stereocontrolpreamplifier
whichhasitsownmastervolumecontrol.
TherighthandpairofAUDIOOUTPUTjacksprovidesaudio
signalcontrolledbytheMR-73frontpanelVOLUMEcontrol.Use
theseoutputjackstoconnecttoexternalpoweramplifier,tape
recorders,oranyequipmentwhichrequirescontinuousfrontpanel
controloftuneroutputvolume.
ACPOWER
PlugtheACpowercordin105voltto125volt,50to60Hzpower
line.ThepowerusedbytheMR73is20watts.
FUSE
A0.5AMP fuseprotectsthetunercircuits.Thisfusedoesnot
protectadditionalequipmentconnectedtothebackpanelACoutlet.
AMANTSWITCH
AdjuststheMR73circuittomatchtheparticulartypeofAMan-
tennaused.EXT.positionisfora conventionalantenna,usuallyof
theoutdoortype,from50to150feetinlength.LOOPpositionisfor
thebuilt-inFerriteLoopstick.
ANTENNACONNECTIONSTRIP
ProvideseasypushtypeconnectorsforanAMantenna,a ground
connection,anda 300ohmFMantenna.
FMANTENNA—75OHM
Providesa typeF connectorfora 75ohmunbalancedFMantenna.
12
MR73

TYPICALHOOKUP
LEFTSPEAKERRIGHTSPEAKER
ACLINE
ACLINE
ACLINE
POWERAMPLIFIERPREAMPLIFIER
MR73
GROUND
(OPTIONAL)
FMANTENNA
AMANTENNA

CONNECTINGTHEMR73
AUDIOOUTPUTS
UsetheFIXEDOUTPUTjackstoconnecttoa conventionalcon-
trolpreamplifierwhichhasitsownvolumecontrol.Fulltuneroutput
isavailableatalltimesfromtheFIXEDOUTPUTjacks.
UsetheFRONTPANELCONTROLLEDjacksto connectto a
conventionalcontrolpreamplifierwhencontinuousfrontpanelcon-
troloftunervolumeisdesired.Thesejacksmaybeusedtoconnect
toexternalequipmentsuchaspoweramplifiersortaperecorders
wherecontroloftunervolumeisnecessary.Thereisnodifference
inthesignalqualityormaximumoutputlevelsavailableateachpair
ofoutputjacks.
Theoutputimpedanceattheoutputsisohms.Longercables
thanarenormallysuppliedcanbeusedtointerconnecttheMR73
withotherequipment.Thelengthofthecableislimitedbythe
capacityofthecable.
Thetotalcapacitymustnotexceed1000pF.Forinstance:cables
witha capacityof25pFperfootmaybe40feetlong;13.5pFper
footcablemaybe75feetlong.Theinputimpedanceoftheother
equipmentshouldbe47,000ohmsorgreater.
CONNECTINGANFMANTENNA
Monophonicinstallationsthataresatisfactoryonanindooran-
tennamayrequiretheuseofanoutdoorantennaforequivalent
stereoresults.Satisfactorystereorequiresabout10timesasmuch
signalfromtheantenna.
Oneofthreeantennasystemscanbeused:(1)theindoordipole
suppliedwiththeMR73,(2)anoutdoorFMantenna,or(3)a VHF-TV
antenna.Infringeareasbestresultswillprobablybeobtainedwith
theuseofanoutdoorFMantenna.Inmanyareastheindoordipole
antennamaybesatisfactory.Theuseofa VHF-TVantennaisalso
effectiveinmanyinstallations.
CONNECTINGANINDOORDIPOLEANTENNA
Theflexiblefoldeddipopleantenna(300ohm)isforindoorusein
urbanorhighstrengthsignalareas.
Connectthetwoleadsfromthedipoletotheterminalsmarked
FMANT(red).Theflexibilityofthethinflatwireassemblypermits
ittobeplacedundera rug,tackedbehindthestereo...or,placed
inanyotherconvenientlocation.Insomecases,itmaybenecessary
to"position"theantennaforbestsignalreception.Thisshouldbe
donebeforeitispermanentlylocated.
CONNECTINGANOUTDOOR300OHMFMANTENNA
Anoutdoorantennaisrecommendedforoptimumperformance
inallareas.Infringe(outlying)areas,bestresultswillbeobtained
witha highlydirectionalFMantennausedinconjunctionwitha
rotator.Rotatetheantennauntilthebestreceptionisobtained.
Connectthe300ohmantennatotheterminalsmarkedFMANT
(red).
CONNECTINGA 75OHMANTENNA
Anunbalanced75ohmantennacanbeconnectedtotheMR73
withcoaxialcable.A "typeF"connectorisusedtocouplethe75
ohmcoaxialcabletotheMR73.
AMBUILT-INANTENNA
FormostlocalandmoderatelydistantAMreceptionthebuiltin
ferriteloopstickantennamaybeused.SettheAMANT.slideswitch
ontheMR73backpaneltotheLOOPposition.
AMOUTDOORANTENNA
ForbestlongdistanceAMreception,usea copperantennawire
50to150feetinlength.Suspendthewireina straightlineashigh
aspossible.Attachthewireateachendwithsuitableglassor
ceramicinsulators.Connecta lead-inwireatanyconvenientpoint
ontheantenna.Itisrecommendedthata lightningarresterbeused
withanoutdoorAMantenna.Thearrestershouldbewellgrounded
toa suitablewaterpipeorcopperoraluminumrodsunkintothe
ground.
Connectthelead-inwiretotheAMANT.pushconnectoronthe
antennaterminalstriponthebackpanel.SettheAMANTSlide
SwitchtotheANTposition.
14

LISTENINGTOTHEMR73
LISTENINGTOAM
TurntheMODESELECTORswitchtoAM.Turnthetuningknob
tothedesiredstation.TheSIGNALSTRENGTHmeterwillindicate
therelativestrengthoftheparticularAMstationbeingreceived.
AdjusttheVOLUMEcontroltothedesiredlisteninglevel.
LISTENINGTOMONOPHONICFM
TurntheMODESELECTORtoFMMONOtolistenonlytomono-
phonicFM.
IfyouwishtoreceivemonophonicFMandhavetheMR73auto-
maticallyswitchtoa stereobroadcastavailableonthesamestation
settheMODESELECTORtoFM.
TurntheSTEREO-FILTERtoOUT.
Turnthetuningknobtothedesiredstation.ThecorrectFMtuning
pointisreachedwhentheFMTUNINGmeterpointercomestorest
anywhereintheblackareaofthemeterscale.Whiletuningacross
thedialyoumaynoticemovementofthetuningmeter,withouthear-
inga station.Thisiscausedbya stationsoweakordistantthat
itdoesnotover-ridethebackgroundnoise.Withultrasonicmuting
inoperationa noisystationofthistypeisautomaticallyrejected.
Toheartheseweakerordistantstations,turntheMUTINGswitch
toOUT.Usuallythelisteningqualityofa stationofthistypewillbe
ratherpoorduetotheweaksignalandstrongbackgroundnoise.
Rotatethedirectionalantennaforbestreceptionasshownby
theSIGNALSTRENGTHandMULTIPATHindicators.
AdjusttheVOLUMEcontroltodesiredlisteninglevel.
LISTENINGTOSTEREOFM
TurntheMODESELECTORtoFM.
TurnMUTINGtoIN.
Turnthetuningknobtothedesiredstation.
TheTUNINGmeterpointershouldbeintheblackareaofthe
TUNINGmeter.WhentheSTEREOindicatorislighted,thestation
isbroadcastinga 19kHzcarrierforstereo.TheMR73willauto-
maticallyswitchtostereo.Ifa stationisbroadcastingmonophonic
FMprogram,theSTEREOindicatorwillremainoffandthetuner
willautomaticallyswitchtomono.
Adjustthevolumecontroltodesiredlisteninglevel.
IfthefixedAUDIOOUTPUTjacksareused,thetunerVOLUME
controlwillnotaffectvolume.
15

YourMR-73FM-AMtunerwillgiveyoumanyyearsofpleasantandsatis-
factoryperformance.Ifyouhaveanyquestionsconcerningoperationor
maintenancepleasecontactthedealerfromwhomyoupurchasedthis
instrumentor:— CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,N.Y.13903
Ourtelephonenumberis
607-723-3512
TAKE ADVANTAGE OF 3 YEARS
OF FREE FACTORY SERVICE
FILL IN THE APPLICA TION NOW
MR
16
GUARANTEE
MclntoshLaboratoryIncorporatedguaranteesthisequipmenttobe
capableofperformanceasadvertised.Wealsoguaranteetheme-
chanicalandelectricalworkmanshipandcomponentsofthisequip-
menttobefreeofdefectsfora periodof90daysfromdateof
purchase.Thisguaranteedoesnotextendtocomponentsdamaged
byimproperusenordoesitextendtotransportationtoandfrom
thefactory.
3YEARFACTORYSERVICECONTRACT
Anapplicationfora FREE3 YEARFACTORYSERVICECONTRACT
isincludedinthepackwiththismanual.TheFREE3 YEARFAC-
TORYSERVICECONTRACTwillbeissuedbyMclntoshLaboratory
uponreceiptofthecompletelyfilledoutapplicationform.Theterms
ofthecontractare:
1.Transportationchargesareexcluded.
2.Thisagreementisgiventotheoriginalpurchaseronlyandis
nottransferable.
3.Theapplicationforthecontractmustbefilledoutcompletely.
4.The3 YEARSERVICECONTRACTisgiventopurchaserswho
liveinthe50UnitedStatesorCanadaonly.
5.Thisagreementisgivenonlyiftheequipmentispurchased
froma franchisedMclntoshdealer.
6.Iftheinstrumenthasbeenmodifiedordamagedbyunauthor-
izedrepairthecontractwillbecancelled.
7.Toreceivefreeservice,thecontractmustbepresentedtothe
factoryauthorizedserviceagency,whentheequipmentis
presentedforrepair.
IftheapplicationisnotreceivedatMclntoshLaboratory,onlythe
serviceofferedunderthestandard90dayguaranteewillapplyon
thisequipment.
73

McINTOSHLABORATORYINC.
2CHAMBERSST.,BINGHAMTON,N.Y.13903
607-723-3512
Designsubjecttochangewithoutnotice.
PrintedinU.S.A.