VAC PA80/80 User manual

VAC PA80/80 POWERAMPLIFIER
Operating Instructions
DO NOT OPENTHISUNIT-NO USER SERVICEABLE PARTS INSIDE.DO NOT
REMOVE THE BOTTOMPLATE.LETHAL VOLTAGES ARE PRESENT WITHIN
THE CHASSIS. DO NOT EXPOSE TO MOISTURE OR OPERATE ITIFWET.
VACUUMTUBES BECOMEHOT ENOUGH TO CAUSE SERIOUS BURNS.NEVER
TOUCH ATUBE WHEN THE UNITISON.ITMAY TAKE SEVERAL MINUTES FOR
THE TUBES TO COOL DOWNAFTER THE UNITISSWITCHED OFF.
DO NOT PLUG INTO AC UNTILALL CONNECTIONS ARE COMPLETED.
Introduction
TheVAC PA80/80 is asingle chassis wide-band low-feedbackstereoamplifier
conservativelyratedat 80 watts per channel. It is tobeoperatedonlyfromthevoltagevisible
on the configuration cardlocatedunder the fuse. Please contact VAC or your dealer ifthe
voltageinyourarea does not agree withthe label. The fuse is aslowblowtypeofthesize
notedon the backofthe chassis. Atube cage is available as anoption.
Theinputcircuit ofthePA80/80 is derivativeofthe Williamson design,whichwas first
publishedinEngland in1947,and was themainstayoftheoriginal high fidelitymovement.
Notable features of this circuit include a direct-coupledinputamplifier and phase splitter,
resulting inlowphase shift, and inherentprecise balance of thephase splitter (if properly
executed)at all frequencies and levels, resulting inexcellentpush-pull balance, stability,and
lowdistortion.
Theoutputstageis derived fromtherenownedPA90C,featuring individuallyadjustable
"fixed-bias"and partial-triode ("ultra-linear") operation.
Premiumparts are employedthroughout, including 14 pound 22 section bifilar-wound ultra-
wideband outputtransformers, polypropyleneand polystyrenesignalcapacitors, high current
rectifiers, lowESR power supply, and proprietarywiring. The qualityof parts and careful
layout allows the use ofverylittle feedbackfor high sonic purityand lowdistortion.

Unpacking
Eachtube socketonthe amplifier is covered byasmall roundsticker.The color ofthis sticker correspondsto
the color ofthe sticker onatube.Fiteachtube intothe matching socket, first removing the sticker fromthe
tube andsocket. The biaslevels for the output tubeshavebeenfactoryset, but shouldbe checkedduring the
installationprocedure.
Installation
Physicalrequirements:
1) Provide adequateventilation- allowat least 3inchesaboveand1inchtoeachside.
2)Donot placein acompletely enclosed cabinet.
3)Donot stackother equipment ontopof the VAC units.
4)Donot operateoncarpet or any other surfacethat might blockairflow.
5)The chassis andpower transformerswill becomehot in normaluse.
6)Donotallowthe chassis ofthe VACcomponentstotouchany metalparts,suchasthe frameofan
equipmentrack.This mightcreateaparallelgroundpaththatwill degrade the soundofyoursystem.
Electricalconnections:
1)Completeall installationsteps before plugging the amplifier intothe AC mains supply.
2)Connectsignalinputstothe power amplifiers.Singleended interconnectcablesequipped withRCA
phonoplugs provide the input toeachchannel.
3)Connectloudspeakersbetweenthe appropriatepairofbinding postsonthe backofthe power
amplifiers.Mostpopularspeakercablescanbeaccommodatedbythe outputposts.Outputimpedance
matching is availablefor loadsof2,4,or 8ohms.Connect onelead of the speaker cabletothe "G"
position,andthe other toeither 2,4,or 8.The "G"terminalis atgroundpotential,andthe amplifier
doesnot invert phase.
4)Donot connect twoamplifier outputstoeachother.
5)Connectthe ACcord tothe power sourceindicated bythe voltageconfigurationcard under the fuse
(100 voltsAC, 120 voltsAC, 220 voltsAC, or 240 voltsAC at 50 or 60 Hertz).
6)Followthe BIASprocedure described in this manualtosetthe idlecurrent. Also,read the section
entitled INSTALLINGNEW OUTPUT TUBES.

Operation
Continuousoperationis notrecommended.Ifthe amplifierswill notbe auditioned for afewhoursitis bestto
turnthemoff. This avoidsunduestress tothe KT88 output tubes.
Aswithall highfidelityproducts, the soundcharacteristics ofthe VACamplifierschangesomewhatasthey
warmup.Bestsoundwill be achieved after 15 minutesofoperation,withsubtlechangesoccurring for upto
onehour.However,weadviseagainstleaving the equipmentonatall timesbecauseofthe attendant
accelerationofoutputtube wear.Lifeofthe outputtubesaveragesbetween2,000 and8,000hoursdepending
uponbrandfitted andrandomvariations within the tubesthemselves.
Any timethatthe VACPower Amplifier hasnotbeenused for afewweeksthe soundmaybe different. This is
alsonormalforhighresolutionaudioequipment. Optimumsoundshouldreturnafter afewhoursofoperation,
preferably withanaudiosignal.
PleasenotethatalthoughyourVACamplifiershavebeenrunfor 48 hoursatthe factory,theywill continueto
"breakin"for approximately150hours.Alsobe awarethatmanycomponentsdisplaythe needforanewbreak
in period after being transported in unheated cargoaircraft.
BiasAdjustment
YourVACPower Amplifier hasbeenshipped withoutput tube biaspreset. This shouldbe checkedwhenyou
install youramplifier, andperiodically thereafter. It must alsobe set whenever anoutput tube is changed.
Adjustmentoftheoutputtubesis quiteeasy,andrequiresonlyasmall screwdriver.Onthefrontpanelare four
bi-colorLEDs,eachwithanadjacentadjustmentcontrol.Viewthe LEDsfromdirectly in front,notfromabove
or below.Adjustthe LEDstobe greenwhenthe amplifier is notplaying music.Toset, turnthe control
clockwiseuntil the LEDjustbegins tochangetoanamber/red color,andthenbackthe controloffjustslightly
torestore the pure greencolor.
Asmusic plays,the LEDswill varyfromgreentored.Checkthe biasifyouever see anLEDstayred while
music is not playing, or if anLED doesnot tendtoward amber or red whenmusic is playing.
Anytubethatcannotbeadjustedtothecorrectbiaspointshouldbereplaced.Anytubewhichrequiresconstant
readjustmentshouldbe replaced immediately.Never operatethe amplifier withanLEDthatshows red when
music is not playing.
Wheninstalling newtubes,setthe biascontrols counter-clockwise.Checkthe biasofbothchannels asthe
amplifier warms up- don't wait tenminutes.
Biaslevelsshouldbecheckedmonthly toensureoptimumsoundquality.Itis notunusualforthebiastochange
withtime,particularly whentubesare new.The greatestamountofdrift occursduring the first200 hoursof
atube'slife.The driftmaychangedirectionperiodically,suchthatthe biascontrolmustbeincreased andlater
decreased, or viceversa. Checkbiasif the soundseems lacking in detail or dynamics.
Tube Types
Theinput/splittertubeandthedrivertubemaybetype12AU7A/ECC82/E82CCortype12BH7(typicallyricher
sound).TheoutputtubesaretypeKT88.GoldenDragontubesaregenerallyrecommendedandhavebeenused
extensively during the developmentofthis amplifier.Pleasefeelfree tocontactVACifyourequire additional
informationor advice.

InstallingNewOutputTubes
Replacementtubesare availablefromVACandother sources.Output tubesare KT88 beampower Kinkless
Tetrodes(6550 mayalsobe used -see Tips&Advice,Output Tubes). Itisnotnecessarythattheybe matched
pairs,althoughaslightimprovementinmeasuredperformancemaybe achievedinthis way.Makecertain that
eachtube fitsfirmly in itssocket. Atube thatfitsloosely maynotmake correctcontactonall pins andmight
"runaway" (read on). It is best not tomix brandsof tubes.
ALLPOWERMUSTBE OFF.Removethe oldtubesafter theyhavecooled down (TUBES BECOME HOT
ENOUGH TOCAUSE SERIOUS BURNSWHENINOPERATIONAND MAYTAKESEVERALMINUTES TO
COOL DOWN). Install the newtubesfirmlyandfully in thesockets,taking care toobservethedirectionofthe
locating ridgeonthe plastic center pin of eachtube.
Followthenormalturnonprocedure andbeginthe BIASprocedure.Whiledoingthis,keepaneyeonthe plate
(theoutermostmetalstructure)oftheoutputtubes.SWITCHOFFIMMEDIATELYIFTHEYBEGINTOGLOW
RED. This indicatesthatthe tube is "running away",being destroyed rapidly byconducting excessivecurrent.
(Note:withsomeKT88saslightdull orangeglowmayoccurover averysmall sectionofthe plate,usually at
anedge.This is acceptableandnotthe sameasrunning away,in whichmostofthe platewill becomebright
orangeor red.)
Tubesmayrunawayfor severalreasons:
1)The tube is not fully inserted in the socket.
2)The tube fitsloosely in the socketandthuscannotmake correctcontact. Suchatube is unusableand
shouldbe returned toitsseller.
3)The tube is defective.
4)The biasis misadjusted.
5)There is aproblemwiththe amplifier. Contact VAC or yourdealer toarrangeservice.
Inthe eventthattroubleis encountered,tryanother tube.Stopifthe problempersistsandconsultwithyour
dealer or VAC.
Followthe BIASprocedure described previously in this manualtosetthe idlecurrentat70 milliamperesper
tube, checking the idlecurrent at 1minute, 30 minutes, 1hour, and2hours.
Replacementof LowLevelTubes
All power mustbe switched off. Allowtubes tocooldown.Removeandreplacewithnewtubesofthe
appropriatetypes, noting the locationof holesin the socket andpins of the tubes.
Replacement tubesare availablefromVAC andother sources.
Ultra-linear or Triode?
Theinputamplifier,phasesplitter,anddriverstagesaretriodetubesoperatedinClassAwithnocut-offorgrid
current. The output stageis connected for partial-triode,well known for lowdistortion,good damping factor,
andhighefficiency.This techniquewasinvented byAlanBlumlein ofEMI in England,andwaspopularized in
the US as"ultra-linear."VAC canconvert amplifierstotriode connectionfor asmall charge.

Care of Chassis & Face Plate
VACchassis are aluminumfor superior electromagnetic performance.The finishis atoughtextured powder
coatpaint. This finishis durablebut canbe scratched or chipped,justasthatofafineautomobilemaybe
damaged.CleaningwithadampclothWHILETHEAMPISSWITCHEDOFFANDUNPLUGGEDshouldsuffice.
Tube Cages (Optional)
Perforated metalcagesare planned asafuture optiontoenclosethe vacuumtubes.Mounting directions will
be supplied withthe tube cagekit.
Need Help?
Pleasecall uswithany questions youmayhave.Itis better toaskthantoguess.Ourtelephonenumberis
(USA) 941-359-2066. Ourfaxnumber is 941-359-2057.

Warranty
This amplifier is warranted for aperiod ofthirty(30)days fromthe dateofpurchase.Inaddition,ifthe
registrationcard(s)is received byVAC along withacopy ofyoursalesreceipt fromanauthorized VACdealer
within this thirtydays,aservicecontractwill be extended tocover yourequipmentfor two(2)years(except
tubeswhichare covered for 90 days). Receipt of yourregistrationcard will be confirmed in writing byVAC.
This warrantyappliesonly tounitssoldtoandoperated byprivateindividuals in the United StatesofAmerica
throughauthorized VACdealers.For warrantyinformationoutside of the U.S. contact the importer ofVAC
equipment for yourcountry. Unitssoldoutside of the U.S. shouldstill be registered withVAC.
ValveAmplificationCompany
4366-C IndependenceCourt
Sarasota, FL 34234 USA
Tel[phone]
Fax[phone]
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Mail this formalong withacopy of yoursalesreceipt assoonaspossibleto:
REGISTRATION FORM
VAC PA80/80
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Tips & Advice
AWord About Tubesin General
Itis atruththateachbrandoftube soundsdifferentin aparticular highresolutioncircuit. This is becauseno
twomanufacturersmake atube typein quitethe sameway,andthecentraltendenciesofthe performance
parameterswilldifferslightlywitheachmaker.Toemphasizethepoint,examinetheplatestructureofanytwo
12AX7fromdifferentmanufacturerswill probably findthattheymaynoteventhe sameshapeandsize.(Be
carefulhere,asoftenatube is made byafirmother thanindicated onitslabel.Inthe heydayoftubesitwas
commontocrossbrandbetweenmajorlabels,suchasGEandRCA.Todaymanylabelsdonotmanufacturetheir
tubesat all, including GoldAero andRAM.)
This sonic variabilitymayatfirstseemaliability,but further thoughtwill revealthatitis anadvantage,just
like the abilitytoadjustVTAonatonearm.The owner ofatube amplifier canselectthosetubeswhichsound
like the realthing in his/her specific system.Ofcourse,ifthe manufacturer youprefer is rare youmaywant
topurchaseafewspare tubesfor the future.
Howlong shouldtubeslast? Ithaslong beenknown in professionalcircles(andprobably nowforgotten)that
atubesuchasthe12AX7willdisplaybetterperformancecharacteristicsaftertwoyearsofcontinualoperation
thanwhenitwasnew.Innormaluseitis notunusualfor alowleveltube tolast10 yearsor longer.Output
tubesareanotherstory,astheyarecontinuallyprovidingsignificantamountsofcurrent.Herethesoundisyour
bestguide.Certainly tubesshouldbe replaced whenthe amplifierscannolonger meetspecifications or when
(ifyouhaveaccess toatube tester)the tube's emissionis significantly down or itstransconductanceis
substantially out ofspecification.Innormaluse,output tubeswill lastatleast2yearsandperhaps more than
10 years.
VACwill be happy totesttubesfor concerned customers.For appropriatefeeswecanprovide
transconductance, idlecurrent and/or aphotographic record of the tube's platefamily curves.

TIPS& ADVICE
AWord About Output Tubes
YourVACAmplifier canuse2differentoutput tube types:the KT88 BeamPower Kinkless Tetrode andthe
6550ABeamPower Tetrode.Weconsider the soundofagood KT88 tobe superior.Properly manufactured
6550/6550A will work,but mayhaveaslightly higher incidenceoffailure in the PA80/80.Feelfree to
experiment withdifferent brandsandtypestocustomize the soundtoyourtastes.
Aswithinterconnectsandspeakercables,eachtube manufacturer's KT88tendstohaveadistinctsoundwhen
used in VACamplifiers,andofcourse the 6550Assounddifferentaswell.Here is abriefsummaryofour
experienceswithcurrently availabletubesfromdifferent sources.
M-OValveCompany/Genalex/GEC KT88 (U.K.) PRE-1970:
Anaccurateandsweettubewithgoodbassquality.Qualityissurprisinglyvariableforapremiumtube.
Worldwide supply is limited. Highly recommended.
M-OValveCompany/Genalex/GEC KT88 (U.K.) POST-1980:
Hard, glaring sound, only fairdetail. Not recommended.
GoldenDragonKT88 (July 1994 andafter):
AnewvariantoftheChineseKT88 developedinGreatBritain.Anverygood tube,closetotheriginal,
great speed, openness, imaging, andbalance. Highly recommended.
Generic ChineseKT88 (including ARS, GoldAero, Ram, Penta, Jolida, etc.):
Actually afairly good sounding tube.Bass qualitysomewhatphasey,somemechanicalsoundduetoa
subjectivedipintheupper-mid-range.Somesamplesmakeratheralarmingnoisesonwarmupandcool
down, oftenheard throughthe speakers.
NationalNL-KT88-USA:
AnewversionontheKT88producedbytheUSarmoftheRichardson'sorganization.Visually
verysimilar tothe originalandsonically satisfying,closetoboththe originalandthe Golden
Dragon. Slightly lightweight sound, but sweet. Veryexpensive.
GoldenDragon6550A:
Excellenttube withmore subterraneanbass andmid-rangezingthanagood KT88.Losesin terms of
easeanddimensionality. Mayhelp wake upasleepy system, but overall less natural. Good sound.
US made RCAandTung-Sol6550:
Early 6550 typein the "coke glass" bottle. Prettygood sound.
GE 6550A (appliestothosemanufactured in USAbyMPD):
Overall hard andlacking in air. Not recommended.
Phillips/ECG/Sylvania6550A:
Similar tothe GE tube, perhaps abit better.
Sovtek 6550:
Samplestested do not biascorrectly, having insufficient current flow. Not recommended.

TIPS& ADVICE
AWord About LowLevelTubes
Thesmalltubes(VoltageAmplifier/PhaseSplitterandDriver)intheVACAmplifiersaretype12AU7.Thistube
is essentially the sameastypes12AU7A,5814,6189,CV4003,ECC82,andE82CC. The qualityofthe tube
used is byfar more important thanwhichof these(equivalent) typesis used.
Thepreferred12AU7AistheBritish/ChineseGoldenDragon.AcceptablealternateversionsincludetheBrimar
CV4003(ladderplateversion),MullardCV4003(verymidrangy),genericChinese12AU7(brighter),Sylvania
6189(darkersound),theGE12AU7A(slightlyforwardandgrainy)andtheYugoslavian12AU7(cohesiveand
somewhat coarse).
Many classic tubesworthtrying ifyouhaveaccess tothem,suchasthosefromTelefunkenandAmperex,
althoughacautionis in order,aswehaverecently seenEastGermanEL34 relabelled "TelefunkenWest
Germany."TubesactuallymanufacturedbyRCA,Westinghouse,andSylvaniacanbe quitegood,butthe name
onthetubedoesn'talwaysindicatewhoactuallymadeit.OthernamestowatchforareValvo,Mazda,Tung-Sol,
Bendix, Mullard, Brimar, andRaytheon.
TIPS& ADVICE
AWord About BiasLevels
The output stageis designed tooperatein richClass AB1atanidlecurrentof70 milliamperesper tube,at
approximately 535 VDCacross the tubes.For more technicalinformationabout classesofoperationsee VAC
TechnicalMonograph90-8.
Somedesignerserroneously marketalower voltageandcurrentoperating point(aslittleas26 mA@550
VDC) as"Class A1."Be assured thatthe VACanditstubesare strong enoughtohandlethe more demanding,
richer biaslevel.

TIPS& ADVICE
AWord About ImpedanceMatching
Westrongly suggestthatyouexperimentwiththe three availableimpedanceconnections for the bestsonic
matchwithyoursystem.Sincenoloudspeaker representsanunchanging impedanceatall frequencies,itis
impossibletoassertwithcertaintywhichoutput tapis appropriatetouse.Inmany systems anamazing
differencein soundwill exist betweenthe variousimpedancetaps.
You shouldconsider the output impedancemarkings onyourVAC Power Amplifier asfollows:
"8ohms" matchesloadsbetween4ohms and8ohms
"4ohms" matchesloadsbetween2ohms and4ohms
"2ohms" matchesloadsbetween1ohmand2ohms
Mostloudspeakersvaryoutsideofanyoneoftheseranges,whichiswhyexperimentationisessential.Weoften
findthat matching aspeaker's minimum impedanceis more importantthanmatching itsnominal (average)
impedance.
Contrarytopopular misconception,nopower is lostduetounused output taps.Also,the amountofnegative
loopfeedbackin the amplifier doesnotchange,being fixed atapproximately 6decibelsfor all outputtaps.For
more informationconsult VAC TechnicalMonograph90-9.
TIPS& ADVICE
AWord About Output StageOperating Mode (triode internalwiring option)
Triode amplificationis the oldestformknown,whilepartialtriode ("ultra-linear")operationofpentodesand
beampower tubesdatesto1937.Fromthe engineering perspective,the triode mode differsfromthe ultra-
linear mode in the following ways:
1)Somewhat more distortionat lowpower levels
2)Somewhat less distortionat moderatepower levels
3)Reduced maximumpower output
4)Output impedancematching is somewhat less critical
5)Increased damping factor.
The ultra-linear mode appliesnegativevoltagefeedbackfromthe primaryofthe output transformer tothe
screens ofthe output tubes.The ultra-linear circuitdisplays differentcharacteristics (efficiency,distortion
componentsandlevels,etc.) depending uponhowmuchofthe primarywinding is commontoboththe screen
andplateofthe output tubes.The VACimplementationofthe ultra-linear circuithasbeenselected toachieve
performancequalityasclosetopure triode aspossiblewhilestill increasing power output andefficiency.
VAC canprovide directions allowing askilled techniciantoconvert the output stagetotriode operation.

SPECIFICATIONS
TheVACSystemhasbeendevelopedwiththecriticalearasthemajorarbiterofquality,withbothconventional
anduniquemeasurementsprovidinginsightandguidanceasnecessary.Thelackofemphasisonmeasurements
is duetothe factthatengineering's arsenalofequipmentandtechniquesdo notoperateonthe pattern
recognitionprincipals that controlhumanperceptionof sound.
Inthe immortalwordsofDanielvonRecklinghausen,ifitmeasuresgood andsoundsbad itis bad.Ifit
measuresbad andsoundsgood you'vemeasured the wrong things.
For thoseconcerned withtestbenchperformance,the following describestypicalmeasured performanceofa
PA80/80 operated at 120 VAC, 60 Hz.
PowerOutput:83 wattscontinuousaveragepowerat1kHz into8ohms connectedtothe 8ohmtap,
bothchannels driven; 86 wattsonechanneldriven.
Frequency Response:down 0.5dB at 5Hz and64 kHz, ref 0dB =1watt @1kHz.
down 3.0dB at 3Hz and115 kHz, ref 0dB =1watt @1kHz.
Power Bandwidth:down 0.5dB at 12 Hz and50 kHz, ref 0dB =80 watts@1kHz.
down 3.0dB at 8.5Hz and85 kHz, ref 0dB =80 watts@1kHz.
Distortion:<.25% THD at 1kHz 10 watts
Noise:<1.5mvat the output, S/N ratio>84 dB
Sensitivity:.775 voltsinput for full power output
NegativeFeedback:Loopfeedbackis fixed at approximately 6dB regardless of output tapselected.
AbsolutePolarity:Doesnot invert signalpolarity.
Fuse:Slo-Blowtype, 4A for 100 &120 Volt configuration, 2A for 220 &240 V.
Power consumption:300 wattsat idle, 516 wattswithbothchannels driventofull power.
Dimensions:18 "widthx15 "depthx7.5"height