McIntosh MC225 User manual

STEREOPOWER
AMPLIFIER
MC225
TABLEOFCONTENTS
GENERALDESCRIPTION1
TECHNICALDESCRIPTION1
ElectricalSpecifications2
MechanicalSpecifications3
PANELFACILITIES4
Input4
Output4
LineOutput4
Fuse4
ACOutlet4
LineVoltage4
INSTALLATION5
CONNECTIONS5
Input—Stereo5
Input—TwinAmp5
Input—Mono6
Output—StereoorTwinAmp6
Output—Mono6
LineOutput—StereoorTwinAmp6
LineOutput—Mono7
ACPower7
OPERATINGTHEMC2257
ADJUSTMENTS7
InputSwitch-Stereo7
InputSwitch-Mono7
GUARANTEE8
FREE3-YEARFACTORYSERVICE
CONTRACTAPPLICATIONcoverpocket
SCHEMATICDIAGRAMcoverpocket
PARTSLISTcoverpocket
RESISTANCEANDVOLTAGECHARTcoverpocket

MC225POWERAMPLIFIER
GENERALDESCRIPTION
Overonemillionwattsofamplifieroutput
powercapacityhavebeenmanufacturedby
Mclntoshsince1947.Inthis1,000,000watts
ofaudiopowertherearelessthan10wattsof
distortioncapacityandlessthan1/100watt
ofnoisecapacity!
Thedramaticdifferenceinthequalityof
musicreproductionwhenyoulistenthrough
Mclntoshinstrumentsisdirectlyduetolow
distortionperformance.Careful,devoted
researchisa wayoflifeatMclntosh.The
world'sfinestamplifieristhecreationofper-
severing,resourcefulMclntoshengineers.
MclntoshLaboratoryistheonlymanufac-
turerintheentireindustrytoguaranteethe
lowestdistortionatallaudiofrequencies,at
fullpower.TheU.S.PatentOfficehasrec-
ognizedtheadvancedtechnologyofthe
Mclntoshcircuitbygranting6 patents.1
Longlife,flexibility,highestqualitycon-
structionarecharacteristicdesignsinevery
Mclntoshinstrument.Wideelectricaland
thermalmarginsofsafetyforallcomponents
andtubes,advancedengineering,andcool
operatingdesignaddtothelonglifebuilt
intoeveryMclntoshproduct.Reliabilitypro-
longsyourinvestmentwithoutexpensive
maintenancecosts.
TheMC225hasononechassistwo25
wattpoweramplifiers.Inadditiontouseasa
stereoamplifier,theflexibilityoftheMC225
permitsittobeusedasa monophonic
amplifierthatdelivers50watts,orastwo
separate25wattamplifierswitheachchan-
nelamplifyingcompletelyseparatepro-
grams,orastwoamplifiersforusewithan
electroniccrossovernetwork.Suchflexi-
bilitypermitsmaximumuseforgreatest
returnfromyourinvestment.
TECHNICALDESCRIPTION
ThepatentedMclntoshUnityCoupled
circuitandoutputtransformerhaveestab-
lishedMclntoshamplifiersastheunchal-
lengedleadersintheaudiofield.
Before1947,lowdistortionathighpower
andhighefficiencywasimpossible.A com-
pletelynewengineeringapproachresultedin
anamplifierthatforthefirsttimepermitted
highpowerwithdistortionbelow1%.That
newengineeringproducedtheMclntosh
UnitycoupledcircuitandtheMclntoshbifilar
woundoutputtransformer.Withtheintro-
ductionoftheMclntoshamplifiernewstand-
ardsfordistortion-freeperformancewere
established.
PRIMARYNO1
turnofprimarynumberoneisnexttothe
sameturnofprimarynumbertwo.Thereis
almostcompletemagneticcouplingbetween
thetwowires.Themagneticcouplingisrein-
forcedbythecapacitancebetweenthe
twowires.
INPUT
OUTPUT
PRIMARYNO.2
Fig.1—Representationofbifilarwinding.
TheMclntoshoutputtransformeris
unique.Ithastwoprimarywindingswhichare
woundbifilarly.Inthebifilartechniqueboth
primarywiresarewoundsidebyside.EachFig.2-RepresentationofMclntoshoutputcircuit.
'U.S.PatentNo's:2,477,074;2,545,788;2,646,467;2,654,058;2,860,192;2,929,028.
1

IntheMclntoshUnityCoupledcircuitone
ofthebifilarprimarywindingsisconnected
throughthepowersupplytotheplateand
cathodeofoneoftheoutputtubes.Theother
bifilarprimarywindingissimilarlyconnected
totheothertube.
Alllowdistortionhighpoweramplifiers
usepush-pulloutputcircuitsknownasClass
AB1,AB2orB.Twotubesarearrangedina
balancedcircuit.Thispermitseachtubeto
operatealternatelysomewhatoverhalfthe
time.Comparedtofulltimeoperationofthe
tubes,thepush-pullmethodreducesheating
andpermitsmorepowerfroma giventypeof
tube.Despitethisadvantageoftheconven-
tionalpush-pullcircuitoneprobleminpar-
ticularremainedtobesolved.Whencurrent
ineachtubeiscutofftobegintheidleperiod
distortionisproducedattheinstantofcut
offandagainattheinstantwhencurrent
flows.Thisformofdistortionisknownas
NotchDistortionandwaswellillustratedby
Mr.PenTungSahinthe"Proceedingsofthe
I.R.E."Volume24,pp1522-1541in1936.
Imperfectcouplingbetweentheprimary
windingsfoundinallconventionaloutput
transformersproducesthenotchdistortion.
Tryingtoimprovecouplingina convention-
altransformerdecreasesthepowerresponse
atbothlowandhighfrequencies,heating
theoutputtubesandloweringtheavailable
poweroutput.
TheMclntoshUnityCoupledoutputcir-
cuitandbifilartransformeristhefirstcom-
mercialbreakthroughthateliminatesnotch
distortionbycouplingbothoutputtubes
almosttoperfection.IntheMclntoshtrans-
formertheextremelyclosecouplingofthe
bifilarwindingsremovestheconditionwhich
permitsnotchdistortion.Furthermorethe
twooutputtubesarearrangedaspartial
cathodefollowers.Halfoftheoutputcircuit
isinthecathodeandhalfintheplateofeach
tube.Theoutputtubesnowareoperatingin
alocalfeedbackloopwhich,reducestheir
distortion,reducestheirinternalgenerator
resistance,andreducestheirbalance
requirements.TheMclntoshcircuitin
realityperfectspush-pullhighefficiency
outputcircuits.
Goodvoltageregulationinthepower
supplypermitsoverloadswithoutovershoot
orblocking,providesgoodtransientre-
sponse,andcompletestability.Toimprove
regulationa siliconrectifierpowersupplyis
usedintheMC225.Inadditiontobetter
voltageregulation,thesiliconrectifierallows
evenhigheroperatingefficiency,cooler
operation,andlongeramplifierlife.
Togreatlyextendtubeandcomponent
lifea thermistorintheMC225limitscurrent
surgesproducedwhentheequipmentis
turnedon.Thethermistorisa specialtypeof
resistor.Itsresistancedependsonitstem-
perature.Whentheamplifierisoffthetherm-
istorhasa highresistancevalue(about79
ohms).Justaftertheamplifieristurnedon
thecurrentwhichflowsthroughthetherm-
istorheatsitandcausesitsresistanceto
decreasetoa lowvalue(lessthan.7ohms).
CurrentisthuslimitedwhentheMC225is
firstturnedonbutisnotlimitedastheunit
warms.
ELECTRICALSPECIFICATIONS
PowerOutput:
Stereoortwinamplifier:25wattscon-
tinuousperchannel
Monophonic:50wattscontinuous
HarmonicDistortion:
Lessthan0.5%atratedoutputorless,
20cyclesthrough20,000cycles.Typical
performanceis0.3%orlessat20cycles
and20,000cyclesatfullpower.Typical
performanceinthemidfrequenciesis
0.1%orlessatfullpower.
2

IntermodulationDistortion:
Lessthan0.5%foranycombinationof
frequenciesfrom20cyclesthrough
20,000cyclesifinstantaneouspeak
powerisbelowtwicetheratedpower.
PhaseShift:
Lessthan±15°20cyclesthrough20,000
cycles
FrequencyRange:
Atratedoutput:
+0,-0.1db18cyclesthrough30,000
cycles
+0,-0.5db18cyclesthrough60,000
cycles
Atone-halfratedoutput:
+0,-1db14cyclesthrough100,000
cycles
NoiseandHum:
90dbormorebelowratedoutput
OutputImpedance:
StereoorTwinAmp:
(Centertapinternallygrounded)600ohms
(Onesideinternallygrounded)4 ohms,
8ohms,16ohms,150ohms,200ohms
Mono:
(Centertapinternallygrounded)300ohms
(Onesideinternallygrounded)75ohms,
100ohms
OutputVoltages:Onesidegrounded
Stereo(ortwinamplifier):
25and70.7volts
Mono(singlechannel):
25and70.7volts
InternalImpedance:
Lessthan10%ofratedloadimpedance
Input:
Inputimpedance:250,000ohms
Inputsensitivity:0.5voltsto30volts
throughgaincontrol.2.0voltswithgain
controlturnedtodotindicator.
PowerRequirements:
117voltsAC,50/60cps
Uses200wattsatratedoutput;85watts
atzerosignaloutput.
Fuse
2.0AmpSloBio
TubeComplement:
VoltageAmplifier—1ea.12AX7
PhaseInverter—2ea.12AU7
DriveAmplifier—2ea.12BH7
Output—4ea.7591
MECHANICALSPECIFICATIONS
Dimensions:
Chassisdimensions:14½"longx 91/8"
widex 7"high.(SeeINSTALLATIONon
Page5 forminimummountingspace.)
Weight:
Chassisonly—34pounds.Inshipping
carton—39pounds.
Finish:
ChromeandBlack
AccessoriesSupplied:
InstructionManual
MountingTemplate
MountingFlanges
Octaloutputplugwithcap
3

PANELFACILITIES
Fig.3—Endpanelshowingallinputandoutputfacilities.
INPUT
TheinputoftheMC225hasa twoposi-
tionleverswitchtopermittheamplifiertobe
usedinoneoftwoways:
(1)Asa monophonic50wattamplifier
(2)Astwin25wattamplifiersusedwithan
electroniccrossovernetwork,ortwo
completelyseparateamplifiers,orin
stereoapplications.
Withtheinputswitchinthe"Stereo"
positiontheinputmarked"L"andtheinput
marked"R"bothhavesensitivitiesof0.5
voltswhentheirgaincontrolsaresetfully
clockwise.Theinputimpedanceofeachis
250,000ohms.Eachgaincontrolallows
signalsourceswithoutputfrom0.5voltsto
30voltstobeconnectedwithoutoverload-
ingtheinputtotheamplifier.Thecontrols
aresetfor2.0voltssensitivitybyturning
themtothedotindicator.
Withtheinputswitchinthe"Mono"
positionthecontrolmarked"RightMono
Gain"setstheinputsensitivityattheinput
marked"R."
TheMONOpositionoftheinputswitch
parallelstheinputstobothamplifiers.When
theoutputsareproperlyconnectedthe
MC225becomesa 50wattmonophonic
amplifier.TheMONOinputGAINcontrol
permitsconnectingsignalsourcesupto30
voltswithoutoverloadingtheamplifier's
input:Theinputimpedanceis250,000ohms.
OUTPUT
Thetwobarrierterminalstripsmarked
OUTPUTprovidestereoconnectionsforthe
normalspeakerimpedancesof4 ohms,8
ohms,and16ohms.Formonophonicopera-
tionconnectionsfor2 ohms,4 ohms,8 ohms,
4
and16ohmsareprovided.Theterminal
stripsmayalsobeconnectedfora constant
voltageoutputof25voltsineitherstereo
ormono.
Assupplied,thesecondaryoftheMC225
isgrounded.
Thebarrierstripoutputconnectionsare
fedfromthesecondaryoftheoutputtrans-
former.
LINEOUTPUT(Seealsopages5,6,and7)
TheoctalsocketmarkedLINEOUTPUT
hasconnectionsfor25volts,70.7volts,and
600ohmsforstereooperationand300ohms
formonophonicoperation.
The600ohmwindingandthe300ohm
windingarebalancedtoground.Pin1 ofthe
octalsocketisthecentertapforthesewind-
ingsandisgrounded.
Theconnectionsattheoctalsocketare
fedfromtapsonthecathodewindinginthe
primaryoftheoutputtransformer.
FUSE
TheMC225usesa 2.0ampereslo-blo
typefuse.TheauxiliaryACsocketisnot
fused.
ACOUTLET
TheauxiliaryACoutletcanbeusedto
supplypowertootherequipmentinthesys-
tem.Theoutletwillprovidea maximumof
400wattsofpower.TheACoutletisnot
fused.
LINEVOLTAGE
TheMC225operatesonlinevoltages
between105voltsto130volts,50cyclesto
60cycles.

INSTALLATION
Adequateventilationshouldalwaysbe
providedintheinstallationofelectronic
instruments.Thetroublefreelifeofthese
instrumentscanbeextendedbyadequate
ventilation.Itisgenerallyfoundthateach10°
centigrade(18°F)riseintemperaturere-
ducesthelifeofelectricalinsulationbyone
half.Adequateventilationisaninexpensive
andeffectivemeansofpreventinginsula-
tionbreakdownbecauseofunnecessarily
highoperatingtemperatures.Thedirect
benefitofadequateventilationislonger,
troublefreelife.
Thesuggestedminimumspaceformount-
ingtheMC225is16"longx 10"widex 10"
high.Alwayssupplyventilationholesinthe
bottomoftheamplifiermountingspaceand
ameansforthewarmairtoescapeatthetop.
TheMC225canbemountedinanyposi-
tionexceptupsidedown.Iftheamplifieris
tobeinstalledona verticalsurfaceitis
recommendedthatthetransformersbeon
thedownside.Theadvantageofthisposi-
tionisthattheflowofheatfromthetubes
risesverticallyanddoesnottendtoheat
thetransformers.
iftheMC225istobepermanentlymounted
usethetwomountingflangessuppliedwith
theamplifier.Theflangesareshipped
separatelyandmustbeattachedtothe
amplifierbottomateachend.
TurntheMC225overwiththetrans-
formersdownandplaceitona pieceofcloth
orcardboardtopreventscratches.The
amplifierisshippedwith4 plasticfeetonthe
bottomcover.Removethe4 plasticfeet.
Removethethreeselftappingscrewsatone
endoftheamplifierthatholdthebottom
covertothechromechassis.Placethe
squareedgeofthemountingflangewiththe
threeroundholespositionedoverthethree
holesinthebottomcover.Thethreeholesin
themountingflangewilllineupoverthe
threeholesinthechassis.Replacethethree
selftappingscrewsthroughthemounting
flangeandbottomcover.Themounting
flangeisnowfirmlyattachedtotheampli-
fier.Repeatthesameproceduretoinstall
themountingflangeontheotherendof
theamplifier.
PlacetheMC225mountingtemplateon
theareawheretheamplifieristobemounted.
Centerpunchthe4 slottedholesinthe
mountingflangesshownonthetemplate.
Removethetemplateandinstallfour#10
roundheadscrewsinthecenterpunch
marks.Donottightenthesescrews.Place
theamplifieroverthescrewheadsandslide
theamplifiertoeithersideintheslotted
holesinthemountingflanges.The#10
woodscrewscanthenbetightenedsecurely.
Fig.4 BottomofMC225withmountingflangesattached.
CONNECTINGTHEMC225
INPUT-STEREOORTWINAMPLIFIER
Theshieldedcablefromtheleftoutput
oftheMclntoshpreamplifierispluggedinto
thejackmarkedINPUT-L.Theshieldedcable
fromtherightoutputoftheMcIntoshpre-
amplifierispluggedintothejackmarked
STEREOINPUT-R.Theinputswitchismoved
to"Stereo."
5

INPUT-MONO
Theshieldedcablefromtheprogram
sourceispluggedintothejackmarked
INPUT-Randtheinputswitchmovedto
"Mono."
OUTPUT-STEREOORTWINAMPLIFIERS
Forstereoortwinchanneloperationitis
notnecessarytousethesamevalueofload
impedanceoneachoutput.Simplyconnect
eachoutputfortheimpedancedesired.
Warning:Donotparalleltheamplifierout-
putswhenusingtheamplifierasa stereo
amplifierortwinchannelamplifier.Damage
totheoutputtubesmayresultifparallel
operationisattemptedwhentheoutputvolt-
agesarenotthesamephaseandamplitude.
Speakersareconnectedatthebarrier
stripsmarkedOUTPUTontheleftendof
thepanel.
IncompliancewiththeNationalElectrical
Code,ClassIIwiringcanbeusedbetween
thespeakerandtheamplifieratthe4 ohm,
8ohm,or16ohmconnection.ClassIIwiring
islampcord,bellwire,orotherwirewith
thistypeofinsulation.Forthenormallyshort
distancesofunder100feetbetweenthe
amplifierandspeaker,#18wireorlarger
canbeused.Fordistancesover100feet
betweentheamplifierandspeakeruse
largerwire.
Theloudspeakerimpedanceisusually
identifiedontheloudspeakeritself.Connect
oneoftheleadsfromtheleftloudspeakerto
thescrewmarkedCOMontheLEFTbarrier
strip.Connecttheotherleadfromtheleft
loudspeakertothescrewmarkedwiththe
numbercorrespondingtothespeakerim-
pedanceontheLEFTbarrierstrip.
Ifthespeaker
impedanceis:
4ohms
8ohrns
16ohms
Connectoneleftspeaker
leadtothescrewmarked
LEFT-COMandthe
otherto:
LEFT-4
LEFT-8
LEFT-16
Connectonerightspeaker
leadtothescrewmarked
RIGHT-COMandtheotherto:
RIGHT-4
RIGHT-8
RIGHT-16
Theonlyadverseeffectontheoperation
ofa Mclntoshamplifierwhenitisimproperly
matchedisa reductionintheamountof
distortion-freepoweravailabletotheloud-
speaker.Closeimpedancematchingisde-
6
sirableformaximumdistortion-freepower.
Usethistabletodetermineproperspeaker
connections:Connectthe
Ifthespeakerimpedance
isbetween:
3.2to6.5ohms
6.5to13ohms
13to26ohms
speakerleads
betweenCOMand:
4ohms
8ohms
16ohms
OUTPUT-MONOPHONIC
WhentheMC225istooperateasa 50
wattmonophonicamplifier,theoutputsof
thetwochannelscombinetoproducea
single50wattoutput.Thischartliststhe
properconnectionsandinterconnectionsfor
monophonicoperation.
Ifthe
speaker
impedance
is:
2ohms
4ohrns
8ohms
Connectonespeaker
leadtothescrew
markedLEFT-COM
andtheotherto:
LEFT-4
LEFT-8
LEFT-16
Connecta
wirebetween:
LEFT-COMand
RIGHT-COM
LEFT-COMand
RIGHT-COM
LEFT-COMand
RIGHT-COM
Connectanother
wirebetween:
LEFT-4and
RIGHT-4
LEFT-8and
RIGHT-8
LEFT-16and
RIGHT-16
WhenconnectedasoutlinedtheMC225
operatesasa 50wattmonophonicamplifier.
LINEOUTPUT-STEREOorTWINAMPLIFIERS
TheoctalsocketmarkedLINEOUTPUT
hasconnectionsfor70.7volts,200ohmsand
600ohms.The25voltlineisfedfromthe
barrierstrips.
For25voltlineoperationconnectoneof
theleftleadstothescrewmarkedCOMon
theLEFTbarrierstrip.Theotherleftleadis
connectedtothescrewmarked16onthe
LEFTbarrierstrip.Connecttherightleads
inthesamemannerontheRIGHTbarrier
strip.
The200ohmand70.7voltconnectionsare
thesame.Toconnectfor200ohmor70.7
voltoperationtheoctalplugsuppliedinthe
hardwarebagisused.Solderoneoftheleft
leadstopin#7andtheothertopin#1.
Solderoneoftherightleadstopin#8and
theothertopin#1.Pin#1istheground
side.
The600ohmconnectionsfortheleftside
aremadebetweenpin#2andpin#3.The
600ohmconnectionsfortherightsideare
madebetweenpin#4andpin#5.The600
ohmwindingisbalancedtoground.Pin#1
ontheoctalsocketisthecentertapofthe
600winding.Pin# 1 isgrounded.

Forallapplicationsusing600ohmsuse
ClassI wiringiftheinstallationmustmeet
therequirementsoftheNationalElectrical
Code.
LINEOUTPUT-MONOPHONIC
TheoctalsocketmarkedLINEOUTPUT
hasconnectionsforoperatingtheMC225
monophonicallyat70.7volts,100ohmsor
300ohms.Foroperatingat25voltsconnec-
tionsaremadeatthebarrierstrips.
Tofeeda 25voltline,connectonesideto
thescrewmarkedCOMontheLEFTbarrier
strip.Connecttheothersidetothescrew
marked16ontheLEFTbarrierstrip.Then
connectwitha wirethescrewmarkedCOM
ontheLEFTbarrierstriptothescrewmarked
COMontheRIGHTbarrierstrip.Connect,
withanotherwire,thescrewmarked16on
theLEFTbarrierstriptothescrewmarked16
ontheRIGHTbarrierstrip.
The100ohmandthe70.7voltconnec-
tionsarethesame.Toconnectfor100ohms
or70.7voltssolderoneoftheleadstopin
#1intheoctalsocket.Theotherleadis
solderedtopin#7. A wireisconnectedbe-
tweenpin#7andpin#8.
Toconnectfor300ohmsoneleadis
solderedtopin#2.Theotherleadissol-
deredtopin#3.Connectpin#2topin#4
witha wire.Withanotherwireconnectpin
#3topin#5.Pin#1isthecentertapofthe
300ohmwinding.The300ohmwindingis
balancedtoground.
ACPOWER
TheMC225operateson105voltto130
volt,50to60cyclespower.Theamplifierwill
beturnedonandoffifitspowercordis
pluggedinoneoftheauxiliaryACoutletson
theprogramsource.
OPERATINGTHEMC225
BeforeturningtheMC225oncheckall
connectionsandplugstoseethattheyare
firmlyandcorrectlyconnected.Checkto
makesurethatthetubesarefirmlyseated
inthepropersockets.Afterthefollowing
adjustmentshavebeencompletedtheMC-
225willoperatewithoutanyfurtherattention.
ADJUSTMENTS
INPUTSWITCH-STEREO
Withtheinputswitchintheleftposition
markedSTEREOtheinputoftheMC225is
connectedtothetwojacksmarked"L"and
"R"INPUTlocatedbelowtheGAINcon-
trols.Theamplifierhasaninputsensitivity
inthispositionof0.5to30volts.
Thetwocentercontrolknobsmarked
GAINshouldbeadjustedtomatchtheinput
sensitivityoftheMC225totheoutputvoltage
oftheprogramsourceequipment.
Tobalancea stereosystemusingthe
STEREOinputpositionusea monophonic
signalfromtheprogramsource.A mono-
phonicsignalsuppliesthesamevoltageto
bothchannels.Turnthevolumecontrolon
thesourceequipmenttothe12o'clockposi-
tion(halfrotation).TurnuptheGAINcon-
trolontheLEFTinputuntiltheloudnessin
theroomisnotquiteasloudasyouliketo
listen.ThenturntheGAINcontrolonthe
RIGHTinputuntilitisequallyasloudasthe
leftchannel.Thesystemisnowbalancedfor
loudnessandprovidesthemostconvenient
amountofloudnesschangewhenusingthe
volumecontrolonthesourceequipment.
INPUTSWITCH-MONO
Withtheswitchintherightposition
markedMONOtheinputsoftheMC225are
internallyconnectedinparallelandtothe
jackmarked"R"INPUT.Thisjackislocated
belowtherightcontrolknobmarked"RIGHT
MONOGAIN."Theinputsensitivityinthis
positionis0.5volt.TheGAINcontrolshould
beadjustedtomatchtheinputvoltagesen-
sitivityoftheMC225totheoutputvoltageof
theprogramsource.
FormaximumflexibilitysettheGAIN
controlasfollows:Turnthevolumecontrol
7

ontheprogramsourceequipment(i.e.tape
recorder,tuner,preamplifier,etc.)tothe
12o'clock(halfrotation)position.Turnthe
"RIGHTMONOGAIN"controlontheMC225
untiltheloudnessofthesoundfromthe
speakerisjusta littlelouderthanyounor-
mallyliketolisten.Thevolumecontrolon
theprogramsourceequipmentnowhasthe
mostconvenientamountofloudnesschange
ineitherdirectionfromthe12o'clockposition.
IMPORTANT
Theexcellentperformancethatisinher-
entinallMclntoshamplifiersdoesnot
dependonthecriticaladjustmentofbiasor
balancecontrolsintheoutputcircuit.The
patentedMclntoshcircuitdeliversitsadver-
tisedspecificationswithoutanyneedfor
thesecontrolsandisnotdependentoncare-
fullybalancedtubesforitsperformance.
WithMclntoshyoucaninstalltheamplifier
andforgetit.
TheMC225youhavepurchasedwillgive
youyearsofpleasantandsatisfactoryper-
formance.Ifyouhaveanyquestionscon-
cerningtheoperationormaintenanceofthis
amplifierpleasecontact:
CustomerService
MclntoshLaboratory,Inc.
2ChambersStreet
Binghamton,NewYork
Ourtelephonenumberis723-5491.
Thedirectdialareacodeis607.
MclntoshLaboratoryIncorporatedguar-
anteesthisequipmenttoperformasadver-
tised.Wealsoguaranteethemechanicaland
electricalworkmanshipandcomponentsof
thisequipmenttobefreeofdefectsfora
periodof90daysfromdateofpurchase.
Thisguaranteedoesnotextendtocompo-
nentsdamagedbyimproperusenordoesit
extendtotransportationtoandfromthe
factory.
3-YEARFACTORYSERVICECONTRACT
Anapplicationfora FREE3-YEARFAC-
TORYSERVICECONTRACTisincludedinthe
pocketinthebackcoverofthismanual.The
FREE3-YEARFACTORYSERVICECONTRACT
willbeissuedbyMclntoshLaboratoryupon
receiptofthecompletelyfilledoutapplica-
tionform.Thetermofthiscontractisdefined
inthe3-yearfactoryservicecontract.Ifthe
applicationisnotmailedtoMclntoshLabo-
ratoryonlytheservicesofferedunderthe
standard90-dayguaranteewillapplyonthis
equipment.TAKEADVANTAGEOF3 YEARS
OFFREEFACTORYSERVICEBYFILLING
INTHEAPPLICATIONNOW.
InCanada:Manufacturedunderlicenseby:
McCurdyRadioIndustries,Ltd.
22FrontStreetWest
Toronto,Canada
Designsubjecttochangewithoutnotice.
GUARANTEE
8

LABORATORYINC.
2CHAMBERSSTREET,BINGHAMTON,N.Y.
Madein U.S.A.
Phone-AreaCode607-723-5491
Form No. 225-HP-761-2MAA-126-161 Printed in U.S.A.