VAC VAC PA100/100 User manual

VACPA100/100 POWER AMPLIFIER
OperatingInstructions
DONOTOPENTHIS UNIT-NOUSER SERVICEABLEPARTSINSIDE.DONOT
REMOVETHEBOTTOMPLATE.LETHALVOLTAGESARE PRESENTWITHIN
THECHASSIS. DO NOTEXPOSETO MOISTURE OROPERATE ITIFWET.
VACUUM TUBES BECOMEHOTENOUGH TOCAUSESERIOUS BURNS. NEVER
TOUCHATUBEWHENTHEUNITIS ON.ITMAYTAKESEVERALMINUTES
FORTHETUBES TO COOLDOWN AFTER THEUNITIS SWITCHEDOFF.
DO NOTPLUG INTO ACUNTILALL CONNECTIONS ARE COMPLETED.
Introduction
TheVACPA100/100 isasingle chassiswide-bandlow-feedback stereo
amplifierconservativelyratedat100 wattsperchannel.Itistobeoperatedonly
fromthevoltagevisible on theconfiguration cardlocatedunderthefuse.Please
contactVACoryourdealer if thevoltageinyourareadoesnotagree withthe
label.Thefuseisaslow blow typeofthesizenotedon theback ofthechassis.
Atubecageis available as an option.
TheinputcircuitofthePA100/100 isderivative oftheWilliamson design, which
was firstpublishedinEnglandin1947,andwas themainstay oftheoriginal
highfidelitymovement.Notable featuresofthiscircuitincludeadirect-coupled
inputamplifierandphasesplitter,resultinginlow phaseshift,andinherent
precisebalance ofthephasesplitter(if properlyexecuted)atall frequenciesand
levels, resultingin excellentpush-pull balance, stability, andlow distortion.
Theoutputstageisderived fromtherenownedPA90C,featuringindividually
adjustable "fixed-bias"andpartial-triode("ultra-linear")operation.
Premiumpartsareemployedthroughout,including14 pound22 section bifilar-
woundultra-widebandoutputtransformers, polypropyleneandpolystyrene
signalcapacitors, highcurrentrectifiers, low ESRpowersupply, and
proprietarywiring.Thequalityofpartsandcarefullayoutallowstheuseofvery
little feedback forhigh sonic purity andlow distortion.

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 notplaying,or ifanLEDdoesnottendtoward amber or red whenmusic is playing.Ifthe flashing of
theLEDsisbothersomewhilelistening,theswitchonthefrontlabelled“BiasTest”canbesetto“0",disabling
the LEDs. The switchmust thenbe set to“1"tocheckthe biasof the output tubes.
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 toensure optimumsoundquality.Itisnotunusualforthe biastochange
withtime,particularly whentubesare new.The greatestamountofdrift occursduring the first200 hoursof
atube'slife.The drift maychangedirectionperiodically,suchthatthebiascontrolmustbe increasedandlater
decreased, or viceversa. Checkbiasif the soundseems lacking in detail or dynamics.
Tube Types
Theinput/splittertubeandthedrivertubemaybetype12AU7A/ECC82/E82CCortype12BH7(typicallyricher
sound). Theoutputtubesare typeKT88.PleasefeelfreetocontactVACifyourequire additionalinformation
or 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.
DONOTusecleaning solutions containing harshdetergentsor solvents.Theymaydamagethe finishor
silkscreened lettering.
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.Ourtelephonenumber is
(USA)941-[e-mail].

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 three (3)years(except
tubes). 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 www.vac-amps.com
4366 IndependenceCourt, SuiteC [e-mail]
Sarasota, FL 34234
Tel[phone]
Fax[phone]
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Mail this formalong withacopy of yoursalesreceipt assoonaspossibleto:
REGISTRATION FORM
VAC PA100/100
Name_________________________________________________________________
Address_________________________________________________________________
_________________________________________________________________
Telephone_______-_______-__________________
Dealer name__________________________________ Salesperson____________________
Dealer address_________________________________________________________________
Purchasedate___________________________SerialNumber___________________
How did you first learnof VAC products?__________________________________________
PleaseprovideanycommentsonVAC productsor your dealer _________________________
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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
12AX7fromdifferentmanufacturers.Youwill probably findthattheymaynoteventhe sameshapeandsize.
(Be carefulhere,asoftenatube is made byafirmother thanindicated onitslabel.Inthe heydayoftubesit
wascommontocrossbrandbetweenmajorlabels,suchasGEandRCA.Todaymanylabelsdonotmanufacture
theirtubesat 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 PA100/100.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.
VAC Tested KT88-T:
The bestoftheversions fromChina,andourcurrentfirstchoice.Good combinationofpunch,air,
sweetness, anddetail. Reliabilityis verygood.
GoldenDragonKT88-M:
Nolongeravailablefromproduction,butanexcellenttube.Abitmorematter-of-factthantheKT88-T,
having more of anNOS US tone, but still preserving the airiness of the KT88.
GoldenDragonKT88, KT88 Classic, KT88 Super:
Generally fairly good for sound; reliabilitysomewhat inconsistent.
NationalNL-KT88-USA:
Aversionproduced bythe US armofthe Richardson's organization.Visually verysimilar to
the originalandsonically satisfying, slightly lightweight sound, but sweet. Veryexpensive.
SvetlanaKT88:
Severalversions havebeenmade,soitis difficulttogiveablanketcomment. The newestversion(as
of summer 2000) shows promise, withasoundsomewhat similar tothe GE 6550A.
US made RCAandTung-Sol6550:
Early 6550 typein the "coke glass" bottle. Prettygood sound.
GE 6550A (appliestothosemanufactured in USAbyMPD):
Somewhat soft andlean, withaslightly buzzycharacter, but fairly sweet.
Phillips/ECG/Sylvania6550A:
Similar tothe GE tube; later productionsamplesmayhaveasomewhat hard upper midrange.
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.
Ifyoubi-wire yoursystem(runseparatespeakerleadsfromthe amplifier tothe highandlowfrequency
transducers)youmaydiscover thattwodifferentimpedancetaps workbest. For example,withearly Martin
LoganSequelIIwefindthatthe bassspeaker isbestmatched withthe 4ohmtap,whiletheelectrostatic panel
is bestcontrolled bythe 2ohmtap.Toachievethis connection,the blackleadsofbothspeaker cablesconnect
to"G",the red lead for the panelconnectsto"2",andthe red lead for the woofer connectsto"4".Withlater
Sequels weusethe 4ohmconnectionfor bothdrivers.
Contrarytopopular misconception,nopower is lostduetounused output taps.Also,the amountofnegative
loopfeedbackin the amplifier doesnotchange,beingfixed atapproximately 6decibels for all output taps.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
recognitionprinciplesthat controlhumanperceptionof sound.
Inthe immortalwordsofDanielvonRecklinghausen,ifitmeasuresgood andsoundsbad itis bad.Ifit
measuresbad andsoundsgood you'vemeasured the wrong things.
For thoseconcerned withtestbenchperformance,the following describestypicalmeasured performanceofa
PA100/100 operated at 120 VAC, 60 Hz.
Power Output:100 wattscontinuousaveragepower at1kHz into8ohms connected tothe 8ohm
tap, bothchannels driven; 103 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 =100 watts@1kHz.
down 3.0dB at 8.5Hz and85 kHz, ref 0dB =100 watts@1kHz.
Distortion:<0.25% THD at 1kHz 10 watts
Noise:<1.5mvat the output, S/N ratio>84 dB
Sensitivity:0.775 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