minirecto25 usermanual

7/29/2019 MiniRecto25 UserManual

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Multi-Watt

Owners Manual

M IN I

TWENTY~F IVE


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Discerning player and all around intuitive human that you are, youe

put your trust in us to be your amplier company. Tis is something we dont

take lightly. By choosing this instrument to be a part o your musical voice,

you hae become much more than a customer to us, youre no a lietime

member o the MESA worldide amily.

WELCOME!Our goal is to neer let you don.

Your reard is that you are no the oner o an amplier bred o a 40 year

heritage in high perormance and it benets fom the many pioneering and

patented MESA eatures and circuits contained in your model. Feel con-

dent, as we do, that this amp ill inspire many hours o musical satisaction

and years o lasting enjoyment.

With you in mind, this amp as designed and built by players ho kno

the value o a ne musical instrument and the commitment it takes to make

great music. Te same commitment to perormance, quality, value and

support we make to you...our ne amily member and fiend.

Hello fom the Home o one


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Readtheseinstructions.

Followall instructions.

Keeptheseinstructions.

Heedallwarnings.

Donotusethisapparatusnearwater.

Cleanonlywithdrycloth.

Donotblockanyventilationopenings.Installinaccordancewiththemanufacturersinstructions.

Donotinstallnearanyheatsourcessuchasradiators,heatregisters,stoves,orotherapparatus(includingamplifiers)thatproduceheat.

Donotdefeatthesafetypurposeofthepolarizedorgrounding-typeplug.Apolarizedplughastwobladeswithonewiderthantheother.

Agroundingtypeplughastwobladesandathirdgroundingprong.Thewidebladeorthethirdprongareprovidedforyoursafety.

Iftheprovidedplugdoesnotfitintoyouroutlet,consultanelectricianforreplacementoftheobsoleteoutlet.

Protectthepowercordfrombeingwalkedonorpinchedparticularlyatplugs,conveniencereceptacles,andthepointwheretheyexit

fromtheapparatus.

Onlyuseattachments/accessoriesspecifiedbythemanufacturer.

Unplugthisapparatusduringlightningstormsorwhenunusedforlongperiodsoftime.

Referallservicingtoqualifiedservicepersonnel.Servicingisrequiredwhentheapparatushasbeendamagedinanyway,suchaspower-

supplycordorplugisdamaged,liquidhasbeenspilledorobjectshavefallenintotheapparatus,theapparatushasbeenexposedtorain

ormoisture,doesnotoperatenormally,orhasbeendropped.

Toinsureproperventilationalwaysmakesurethereisatminimumfourinches(101.6mm)ofspacebehindtherearoftheapparatus.

Theventilationshouldnotbeimpededbycoveringtheventilationopeningswithitems,suchasnewspapers,tablecloths,curtains,etc.

Donotimpedeventilationbyplacingobjectsontopoftheapparatuswhichextendpasttherearedgeofitscabinet.

Nonakedflamesources,suchaslightedcandles,shouldbeplacedontheapparatus.

Theapparatusshallnotbeexposedtodrippingorsplashingandnoobjectsfilledwithliquids,suchasvases,shallbeplacedon

theapparatus.

WARNING:Toreducetheriskoffireorelectricshock,donotexposethisapparatustorainormoisture.

TheACplugisthemainsdisconnect.Theplugshouldremainaccessibleafterinstallation.

WARNING:EU:permissionfromtheSupplyAuthorityisneededbeforeconnection.

WARNING:Alwaysmakesureproperloadisconnectedbeforeoperatingtheamplifier.Failuretodosocouldposeashockhazard

andmayresultindamagetotheamplifier.

Donotexposeamplifiertodirectsunlightorextremelyhightemperatures.

Alwaysinsuretheamplifierisproperlygrounded.AlwaysunplugACpowercordbeforechangingfuse,tubesorremovingchassis.

Useonlysametypeandratingwhenreplacingfuse.

Avoiddirectcontactwithheatedtubes.Keepamplifierawayfromchildren.

Toavoiddamagingyourspeakersandotherplaybackequipment,turnoffthepowerofallrelatedequipmentbeforemakingthe

connections.

Donotuseexcessiveforcewhenhandlingbuttons,switchesandcontrols.Donotusesolventssuchasbenzeneorpaintthinnertocleantheunit .

AlwaysconnecttoanACpowersupplythatmeetsthepowersupplyspecificationslistedontherearoftheunit.

Exportmodels:Alwaysinsureunitiswiredforpropervoltage.Makecertaingroundingconformswithlocalstandards.

READANDFOLLOWPROPERUSAGEINSTRUCTIONS

YOURAMPLIFIERISLOUD!EXPOSURETOHIGHSOUNDVOLUMESMAYCAUSEPERMANENTHEARINGDAMAGE.

Your MESA/Boogie Amplifier is a professional instrument. Please treat it with respect and operate it properly.

ImportantSafetyInstructions


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OVERVIEW ______________________________________________________________ 5-6

FRONT PANEL CONTROLS

Getting Started & Helpul Hints _________________________________________________ 7

CHANNEL MODESChannel 1: Clean / Pushed ___________________________________________________ 7-8Channel 2: Vintage / Modern ___________________________________________________8

Multi-Watt Power ___________________________________________________________ 8

THE CONTROLSGain, Treble _______________________________________________________________ 8-9Mid, Bass and Presence ____________________________________________________ 10-11Master ____________________________________________________________________ 11Standby and Power On _______________________________________________________ 11

REAR PANEL CONTROLS, SWITCHES & JACKS

Speakers ___________________________________________________________________ 13FX Loop __________________________________________________________________ 13AC Socket _________________________________________________________________ 13Fuse ___________________________________________________________________ 13-14

Factory Sample Settings (2 Channels) _________________________________________ 15-17Personal Setting Sheets _____________________________________________________ 18-20Tube Description & Task Charts ________________________________________________ 21Tube Noise & Microphonics ___________________________________________________ 22

Diagnosing Pre-Amp Tube Problems _____________________________________________ 23Speaker Impedance & Possible Hook-Up Schemes - Amplifer to Speaker Cabs __________ 24-28Bias Adjustment by Randall Smith ___________________________________________ 29-31Triodes, Pentodes & Irishmen by Randall Smith _________________________________ 32-34Parts Chart _________________________________________________________________ 35

Multi-WattMini Rectifer Twenty-Five

TABLE OF CONTENTS


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5PAGE

Multi-WattMini Rectifer Twenty-FiveOwners Guide & Operating Manual

CONGRATULATIONSonyourchoiceoftheMiniRectifierTwenty-FiveandWelcome to the MESA Family.Theinstrumentyouhavechosenridesatopa20-yearlegacyofworld-classhighgainperformanceandhit-makingsoundsthathavebeenatthecoreofandevenacatalystforsomeoftheverybestofModernRock.YouwillquicklyfindthatitsMinimonikerandphysi-calsizebearnoresemblancetoitsstature,powerandcommandoverblistering-tightoverdriveintherealmofbiggainTone.

Dontthinkforamomentthisisatrendydown-linetoyormarketing-derivedimitationofourmightyRecto.Thisis therealdealineverywayahigh-endinstrument.Lurkingwithinthisexpensivemetalchassis,liesoneofourmostexpressiveandnuance-enhancingcircuitstodateanditcreatesanexciting,adrenaline-producingTonemachineoneofthemostfuntoplayintheentireMESAcollection.

WhetheryourerockinhardorputtingtheimmenseversatilityoftheMinisfourModestobearonavarietyofstyles,youllgetyearsofinspirationandenjoymentfromthislittlegas-in-glass-poweredjewel.Wealwaysstrivetobuildclassics,iconsthatyoulltreasureamongstyourmostvaluablemusicalinstruments.FromthefeedbackwevereceivedthusfaritseemstheMiniRectoisonitswaytowardachievingthatstatus.

Overview Likeitsoriginaltwochannelforefathers,thisRectokeepsthingsstraightaheadandeasytonavigate.ThisgenerationfeaturestwofootswitchableChannelsthateachcontaintwoModesandwhileitlooksbasicanddriveseasy,aworldofstylisticversatilityliveswithinthesetwosimplerowsofcontrols.

CHANNEL1(Greenindicator/topchannel) ,focusesonrhythmsounds,bothcleanandoverdriven.TheCLEANModedeliverssparkling,big-headroomrhythmsoundsthatbreathewithrich,warmaironthebottomend.Whendriventoclipandcombinedwiththe10wattPowersetting,thisModemisbehaveswithrealattitudeandshinesforurgent,yetsoulful,BluessolosoundsandfurryRockrhythm.PUSHEDaptlydescribeswhattodowiththesecondModeinChanneloneandhereyoullfindthenextregionofgain.WithamorestrippedEQandjustenoughaddeddrive,PUSHEDinvitesaggressiveRockrhythmandCrunchstylestothepartyandeventauntsyourmid-gainsolowork,especiallyinthe10WattPowersetting.

FRONT PANEL:MINI RECTIFIER Twenty-Five Head

REAR PANEL:MINI RECTIFIER Twenty-Five Head

INPUT

FT SW

GAIN TREBLE MID PRESENCE MASTERPOWER

STANDBY

CLEAN

PUSHED

VINTAGE

FT

SW

CH 1

CH 2

MODERN

25 WATTS

10 W

ON

ON

BASS

25 W

10 WATTS

M INI

TWENTY~FIVE

CAUTION:Unplug powerbefore replacingfuse

FXLOOP

HARDBYPASS

120 V~60 Hz

1 A

1 ASLOBLO

8 OHM

CAUTION: CHASSIS SURFACE MAY BE HOT! 4 OHM

SEND

RETURN

HANDBUILTINPETALUMA, CAALL TUBEAMPLIFIER

CAUTION! WARNING!

TUBE GUIDE5 x 12AX72 x EL 84

PATENTED6,621,9077,602,927

S

P

K

R

S

F

X

L

O

O

PRECT I F I ER

MIN I-TWENTY -FIV E

DYN A -W ATT


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6PAGE

CHANNEL2(Redindicator/bottomchannel),featurestheiconicRectohighgainsoundsinboththeirfaces,theiconicliquidwallofVINTAGEandtheaggressivefuryofMODERN.

VINTAGEexcelsatthick,highgainchordingandsinglenotesoloingwithanelasticfeelandabroadharmonicspread.Ithasalooser,moreorganicsoundandtheoverdrivedrapesitselfaroundthenotescreatingahuge,three-dimensionalimage.VIN-

TAGEsoloworkisfurtherenhancedbythe10WattPowerposition.Here,theattackenvelopechangesandbecomesrounderandmorevoice-like,whileupperharmonicsrecedeslightlytocreatesinglenotesoundsoftruebeauty.VINTAGEand10WattcomplimenteachotherinwaysthatwillopennewdoorsfortheRectothatwerepreviouslyopenonlytomorewellbehavedorculturedamps.Itmayalsoopenwidetheeyesofcurrentbig-powerRectoownerswhoexperienceforthefirsttime,whatthispowerrange/wiringstyledoesforasoundtheyhadtypecast.ThisisanewandexcitingfaceofRectoand itwillsurelyexpanditsstylisticfootprint.

MODERNistheoppositeineveryway.ThisaggressiveModecomesrightatyou-maybeevenforyou-withstunningattackandahi-midbumpthatkeepsthingspercussiveandtrackingwithhyper-accuracy.Itisalmosthardtobelievethatthisamountofgaincanbeinfusedandyetstilldeliveraresponseespeciallyinbassfrequencieswiththismuchspeedanddefinition.ButthisispureRectoandMODERNcontributesanequalparttoachievingitsstatusastheothermostrecordedsoundinRock.Needlesstosay,MODERNisallaboutallthingsHeavyandMetal.Andwhilethissoundisbestdemonstratedusingthe25Watt

Powersetting,besurenottotypecastMODERNtooquickly.Usingthe10WattPowersettingtosweetenthemidsandsoftentheattackhere,showsanothersidetoMODERNaswellthatsmoreforgivingandvocal,creatingagreatalternatesolovoicewithalittlemorepunchanddynamiccontent.

Wekeepsayingit,butitshardtooverstatethevalue,effectivenessandstylisticpoweroftheMulti-WattChannelAssign-ablePowerswitches.Thesededicatedwattagerangechoicesunveildifferentpowercharacteristicsandcolorssotheyarereallypowervoicingswitchesaswell.InthisRecto,thechoiceofEL84powertubeswiththeiramazingclipcharacteristics,promptedustoexplorethedifferentwiringschemespossible.Thisexperimentationledtothe10WattPowerModebeingwiredforTriodeoperation.Thismorevintagewiringschemesweetensandroundsoutthesound,turningwhatmightotherwisebealowervolumeversionofthesamevoice,intomoresoulfulRectoexperience.Usethe25Wattsettingforitsboldattack,tighttracking lowend, increaseddefinitionandall outheadroom.Thissettingworksgreatwithall thesoundsandcer tainlyshowcasesthemightinessintheMiniRec,shockingunsuspectingplayersandbystandersalikewithpowerandsonicsize.But

anytimeyouneedtotamethislittlebeastandputavintagepatinaofwarmthandsilkinessaroundthingskickdownto10WattsandenjoyawholenewanddifferentworldofRectoexpression.

JumpingaroundtotheRearPanel,youaremetwithalessoninelegantsimplicity.NothingherebuttheACPowerSocket,theLoopandtheSpeakerOutputs.WhilethisstandsinstarkcontrasttomanyotherMESAmodels,includingtheMinisbigpowerRectobrothers,itwasadecisionbasedonstylistic,genre-appropriatetraditionsandnotacostcuttingroadtoapricepoint.Infact,manyfanshaverequestedsimplerfeaturesetsfromusovertheyearsandthelunchboxformatistheperfectarenaforthisconceptualdeparture.

TheEffectsLoopontheMiniiswiredinSerieswiththedrysignalandisHardBypassableforthosepuristswhoprefertoaddprocessinglaterinthestudioenvironment.Ironically,ourtestshaverevealedthatnearlyallplayersoptfortheLoopengaged

permanantely,citingenhancedrichness,athreedimensionalqualityandanopennesstothesound.WearepleasedbytheaddedjuicethesetubestagesimpartonthesignalasitsnoeasyfeattoaddaLoopthatenhances-ratherthanrobs-Tone.

Wellthatwrapsupthefly-byoverviewoftheMini.NowitstimetogetintotheModesandControlsofthislittledynamo.


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7PAGE

INPUT

FT SW

GAIN TREBLE MID PRESENCE MASTERPOWER

STANDBY

CLEAN

PUSHED

VINTAGE

FT

SW

CH 1

CH 2

MODERN

25 WATTS

10 W

ON

ON

BASS

25 W

10 WATTS

M INI

TWENTY~FIVE

FRONT PANEL: Controls & Features

HELPFUL HINTS 1)Whenpoweringup(especiallyfromacoldstart),alwaysallowthepowertubestimetowarmupbeforehittingthemwithhighvoltage(STANDBYONandplaying).TurnPOWERtoON,waitatleast30seconds,thenturnSTANDBYtoON.

2)Thecenter(3position)minitogglejusttotheleftoftheSTANDBYandPOWERlabeledFTSWprovidesmanualaccesstotheChannelswhentheFootswitchisnotconnected.ThetoppositioncallsupChannel1,thebottompositioncallsupChannel2.TousetheFootswitchtoaccesstheChannels,selecttheFTSW(centerposition)andconnecttheFootswitchtothejackontheleftbottomoftheFaceplatelabeledFTSW.

3)Agoodgeneralruletofollow;AstheGAINgoesup,theBASSshouldcomedown.Thiswillhelppreventlow-endflubandtubbinessandkeeptheattacktrackingtighter.ThisisespeciallytrueintheCLEANandPUSHEDModesofChannel1andalsotheVINTAGEModeofChannel2whensearchingforclippedsoundsthatliesomewherebetweencleananddir tyandmaxedGAINsettings.

4)Youwillexperiencemorefootswitchingnoise(pop)whenswitchingbetweenChannelswhenonlyoneissettothe10WPowersetting.Thisisduetothemoreradicalvoltagechangesthatoccurwhenknockingthepowersectiondowntothe10Wlevelfromthehigher25wattpowermode.(UsingbothChannelsin10Wwillnotcreateexcessnoiseasthevoltagedoesntchangesoradically).MaywesuggestwhenconfiguringyourChannelsforliveperformancefootswitchingapplications,tryusingthe25Wpowermodewheneverpossibleastherewillbenovoltageswing.Thiswillprovidethequietestfootswitchingperformance.

CHANNEL MODESEachoftheRectostwochannelscontainachoiceofmodes-twoinChannel1andtwoinChannel2,sothateachchannelmaybeconfiguredforanarrayofsounds.TheseModeSelectminitogglesradicallyalterthevoicingoftheChannelandmanyinternalchangesoccurasyouswitchthroughtheModes.Howyouchoosetousethesedifferentmodesisuptoyou,butwethinkyouwillagreethatthisschemeprovidessomeofthemostversatilefootswitchingavailableanywhere.

CHANNEL 1: CLEAN / PUSHED CLEAN:ThisisthelowestgaincircuitoftheMiniRectosfourmodesandisoptimizedforproducingbalancedpristinecleansounds.Forthebestunderstandingofhowtoachieveagreatsoundinthismode,please

refertotheGAINControlsectionofthismanual.However,agreatplacetostartis12:00orsoontheGAINControlwithmoresparkleavailablebelowthisandmorewarmthapparentabove...from

there,adjustaccordingtoyourguitarsindividualresponse.

Becauseofitsmoretraditionalarchitecturethismodealsoworksextremelywellforvintagestyledrivesounds.AsmentionedearlierintheOverview,thesesoundsareenhancedbycouplingthemwiththe10WattPowerselectionwhereyoucancombinevintagepreampresponsewithauthenticpoweroverdrive.Byturningthegainallthewayup,abeautifulvintagesolosoundispossible,es-

peciallywithnecksinglecoilpick-ups.TheTREBLEandMIDDLEControlscanalsoaddgainandsustaintothissound(reducePresencetoblendhighs),butyouwillprobablywanttoruntheBASSControlbelow10:30toavoidflubbinessandpreserveafocusedattack.

INPUT

FT SW

GAIN

CLEAN

PUSHED

VINTAGE

MODERN


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8PAGE

PUSHED:Thismodeisaradicaldeparturefromthesweet,shimmeringblendoftheCLEANmodeslowgaincharacter.Hugeincreasesingaininthefirststagesofthepre-ampproduceoneofthebiggestdifferencesbetweenallfourmodesandtransformswhatyouthoughttobeatameandgentlecleanchannelintoaragingcrunchmachine.Thisincredibleamountofgain(foralowgaincircuit)alsocreatesoneofthemostexpressivesolomodesinyourRecto.Becausetherearelessstagesofgainforthesignaltotravelthroughandthetonecontrolnetworkistunedforthebrighternatureofcleansounds,thismoderespondsmorequicklytoyourpickattackandhasamoreurgent,snappyfeel.DontoverlookthismodeforsomeoftheMiniRectoscoolestoverdrivesolosounds.

NOTE:WhenusingPUSHEDwiththeGAINControlmaxed(5:30),avoidsettingtheTREBLEControlhigherthan(2:30).Settingsabove(2:30)maygeneratemicrophonicoscillationincertainpreamptubesintheV1position.ThiscanbeavoidedaltogetherbysettingtheTREBLEControlsensiblywhentheGAINControlismaxed.UsethePRESENCEControlforadditionalbrightness.

CHANNEL 2: VINTAGE / MODERN VINTAGE:ThishighgainmodeisthefamousliquidRectovoice.Itslushharmoniccontentandfatcreamyfeelisfeaturedinsomanyrecordingsandisnowastapleforsomanyheadedtothestudioforanalbum

project.Combiningthissuperjuicy,expressivepreampwiththeRectosblackmagicpowersectioncreatescolorsingainthatmostplayersfindtrulyaddictive.SinglenotesoloworkiseffortlessasthestringsbecomeeasytoplaywiththeVINTAGEmodesmusicalandnaturaltubecompression.SpendtimelearningthelowerregionsoftheVINTAGEmodeasthisisaplacewheremanybeautifulsoundslive.

MODERN:Aggressive.ThisisthewordthatbestdescribesthemenacingpowerofthisRectosmostrebelliousofallmodes.Atake-no-prisonerscrushingassaultoftopendcutandlightningfastre-

sponsecreatesasoundofunparalleledaggressionthathassetanewstandardforhardcoresounds.TheaddedtightnessofthelowendresponsecombinedwiththeradicallymorepresenttopendkeepstheMODERNmodetrackingaccuratelyevenatextremegainsettings.

MULTI-WATT POWER EachChannelcontainsourpatentedMULTI-WATTpowerswitchthatallowsyoutochooseeither25WattsofPentodewiredpoweror10wattsofTriodepowerenablingyoutomatchthepoweroutputandfeeltoeach

ofyourfootswitchablepreampsounds.The10WATTposition(switchdown)rewirestheoutputtubestoTriodestylewiringforavintage-voicedandoh-so-clippable10wattsofpower.Thisproducesasmoother,roundervoicethatclipswithawarmerattackcharacteristicandacreamierfeel.

The25WATTsetting(switchup)bringsonlineourpatentedDyna-WattPentodebasedwiringforthefullpowerandheadroom.Thissettingispreferredforpristinecleansoundsandtight-trackinghighgainsoundsasitdeliversaburstofpowerandheadroomfarbeyondtheexpectationofitsratedpower.ThisingeniousanduniqueMESAcircuitstoresupvoltageinthepowersectionandreleasesitattheinstantof

attackwhenyouneeditthensagsdowntoamorenormalvoltageatatime-specificrate.Allthistranslatesintoabouncy,dynamicsoundandanamazing,precise,yetelasticfeelonthestrings.Puretubemagic!ThiscircuithasbeenappreciatedbyplayersaroundtheworldfordecadesandhasfurtheredtheoriginalBoogielittleampthatcouldlegendsinceitsintroductioninthenow-classicStudio22backin1983.

THE CONTROLS

GAIN Thiscontroladjuststhepredominantgainstageineachchannelscircuitwiththefunctionandtaperbeingoptimizedforeachindividualchannel.RememberthatyourRectoisreallytwoseparatemulti-modeamplifiersbuiltontoonechassis,sothougheachchannellooksidentical,theGAINControlforeachchannelcomesoninadifferentplaceandadjustsadifferentpointinthatchannelscircuit.

Inmostguitaramplifiers,andespeciallyinall-tubecircuits,theGAINControlisthemostpowerfulcontrolinthepreamp.Itshapestheoverallstyleandcharacterofthesoundandisresponsibleforwhetherthesoundisclean,overdrivenoranywhereinbetween.InyourRecto,theGAINControlisevenmorepowerful.Itnotonlydeterminestheamountofdrive,butalsoactsasanintegralpartofthetonecontrolstringaswell.

MASTER

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW

GAIN

CLEAN

PUSHED

VINTAGE

MODERN


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9PAGE

TosimplifytheGAINControlsroleinshapingtheoveralltoneofthesoundwewilllookatitintwoways:1)aloneand2)inconjunctionwiththetonecontrols.

1)GAINControlhasthreetonalregions:LOW(7:00-11:00)providesthecleanest,leastsaturatedsoundsandinthisregionthesoundwillbebrighterandcontainmoreupperharmonicslendingathreedimensionalcharactertothesound.

MIDDLE(11:15-2:00)enhancesthesaturationandreplacessomeoftheupperharmon-

icswitharicher,warmerqualityandafullerbottomendresponse.Notyetfullysaturated,thisregionistheeasiestplacetogetagreatsoundinbothchannels.ThisregioncontainsmanyoftheRectosbestsounds...especiallyforsoloingduetothecrucialblendofanexpressiveattackcombinedwithamplesustain.

HIGH(2:15-5:00)saturatesthesignalandenhanceslowandlowmidfrequencies.Whilethisregionprovidesthemaximumsaturationandsustain, italsocompressesandsoftenstheattackcharacteristics.ForthisreasonwesuggestusingthishigherregionoftheGAINControlsparinglyandonlywhenmaximumsustainisneeded.

NOTE:DuetotheRectosextremegainpotential,thehighestregionsoftheGAINControlmaypossiblypushthepre-amptubespastwhattheycanhandle,producingmicrophonicsquealing.Whilewescreenandtestthetubesyouramplifierwasshippedwithandthetubesinyouramppassedourrigouroustest,wecantpredicthowthetubeswillrespondovertimeexposedtoextremegainsettings.Yourtubesarewarrantedforaperiodof6monthsundernormaluse,butyoucansaveyourselfthepresentandfutureinconvenienceofhavingtodealwithannoyingmicrophonictubeproblemsbysimplyusingalittlecommonsense...DontturntheGainallthewayup!

Ifyoumustforaspecificpartoratverylowvolumes,backdowntheTREBLEandPRESENCEControls.YourRectowasde-signedtoprovideamazinggainandtoneatlessthanextremesettings-removingtheneedforyoutocrankeverythingallthewayup.Ifyouarenotabletoachievethesoundyouwantatsensiblesettingsonanyorallofthecontrols,yourproblemmaylieelsewhereinthesignalchain,i.e.pick-ups,cabinetry,processingetc.Keepinmindyoucanalwayscallononeofourprod-uctspecialistMondaythroughThursdayandseeksomeadviceshouldyoufindyourselfstrugglingtogetthesoundyouwant.

2)GAIN-InconjunctionwiththeToneControls-Basically,asimpleruleapplies...astheGainisincreasedtheTonecontrol

stringhaslessandlesseffectonthesignaluntilat5:00,thesignalissosaturatedthatyouaregettingmostlyGainandverylittleTone.Again,thisisthereasonwesuggestusingtheGAINControlinitsmiddleregion.Here,theTonecontrolstringisveryactiveandprovidesmaximumshapingpower-allowingyoutodialvirtuallyanysoundyoudesire.

TREBLE Asinmosttubeguitaramplifiers,theTREBLEControl(inbothchannelsofyourRecto)isthemostpowerfulofthetonecontrolsandisnextinlineonlytotheGAINControlasashapingtool.Becauseitisfirstinthesignalpathofthetonecontrols-andfromheretheMiddleandBassreceivetheirsignal-itisbyfarthedominanttonecontrol.Forthisreasontheset-tingoftheTREBLEControlisveryimportantforequalrepresentationofthethreefrequencyregionstoappearattheirrespective

controls.LikemostofthecontrolsonyourRecto,thereisanoptimumregionoftheTREBLEControlwhereampletopendismixedinandyetenoughsignalisstillpassedontotheMIDDLEandBASSControls.

Asyoumightsurmise,11:00-1:30isthesweetspot.Therearedefinitelygreatsoundsaboveandbelowthismiddleregion,butthebalancebetweentheTREBLEControlandtheothertwotonecontrolsiscompromised.

TheoneplaceyoumaywanttothrowcautiontothewindandsettheTREBLEControlabovethismedianzonepresentsitselfinChannel1ofyournewRecto.Inbothmodes(Clean&Pushed),theTREBLEControlcanbeusedtodumpextragainintothemix.ThisisespeciallyeffectiveinthePUSHEDmodeforcrunchsounds.WhendoingsousethePRESENCEControltorolloffsomeofthemorethanampletopendfora

morecompressedfeelandfattervoice.TheBASSControlseffectivenesswillbereduced,soyoumayhavetorunamuchhighersettingthanyouareusedtoseeingtoachieveabalance.Thissaid,keepinmindthattheTREBLEControlinChannel1Pushedshouldnotbesetmuchabove3:00toavoidunwantedmicrophonictubeproblems.

GAIN

CLEAN

PUSHED

VINTAGE

MODERN

GAIN REGIONS

BrightestMost Balanced

Warmer & Saturated

TREBLE

SWEET SPOT


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10PAGE

MID TheMIDControlisresponsiblefortheblendofmidrangefrequenciesinthemixandthoughitseffectisnotasdramaticasthatoftheTREBLEControl,itplaysanintegralpartinachievinganysoundinyourRecto.Itiscapableofchangingthefeeldramaticallyasitblendsinagroupoffrequenciesthattendtosoftenorstiffenthewayasoundfeelstoplay.

MostplayerstendtoleaninthedirectionoflowerMIDDLEControlsettings(7:00-11:00)whereascoopinthisregionpro-ducesgirth(bylettingtheBassbecomealittlemoredominant)andalackofpunchlendsamorecompressed,evenfeeltothestringsandthereforelessapparentresistancetothepick.AstheMIDDLEControl isincreased,(11:30-1:30)thesound

isrounded-outandfilled-inwithafocusedmidrangeattackappearingratherquickly.Asyouwouldguess,thefeelstartstochangebecomingslightlymoreresistant.AbovethisregiontheMIDDLEControlcouldbeused tocompensate foreitherweakerpick-upsorfor timeswhenaspecificdeficiencyiscreatedeitherbyanextremelyhighsettingofothertonecontrols,oraphysicalanomalyintheroom.WhiletheseMIDDLEControlsettings(2:00-5:00)canintroduceaddedgainandcreateenhancedfocus,thetrade-offwillbeastiffer,moreforward,lesscompressedfeel.

Channel1utilizesadifferentMIDDLEControlthanthatoftheChannel2withacustom-designedtaperandvalue.Initslowrange(below12:00)itfunctionsasanormalmidrangecontrolwithatapersuitedtoblendingfineincrementsofthesefrequen-cies.Mostplayersleantowardafairlyradicalscoop(7:00-10:30)forcleanplaying,preferringtoletTrebleandBassremaindominant,thusproducingthesignaturesparkleandbreathessentialforapristinecleansound.

AsChannel1sMIDDLEControlissweptpast1:00,itstartstoaddgaininthesemidrangefrequenciesaddingcutandpunch.Asthetopendofthecontrolisreached,(3:00-5:00)itbecomesanadditionalgaincontrolcapableoftakingbothCLEANandPUSHEDmodestoextremes.Experimentwiththiscrankedregioninconjunctionwithconservativesettingsoftheothertonecontrolstobalancebothsoundandfeel.WhilethisaddedflexibilitymaymakeChannel1sMIDDLEControlalittlemoretrickytolearnatfirst,itwillbecomequitevaluableasyoustarttorealizethepowerofthissuperversatilechannel.

BASS Last,butnotleastinthestringoftonecontrols,wecometotheBASS.Thiscontrolworkssimilarlyinbothchannelsinthatitdeterminestheamountoflowfrequenciespresentinasound.However,theactualfrequenciesandstyleoflowsitmixesinchangeswiththechannels.LiketheMIDDLEControl,itfallsinlinesignal-wiseaftertheTREBLEControlandthesameschemeapplies.WhentheTREBLEControlissethigh,theeffectivenessoftheBASSandMIDDLEControlsisreduced.IftheTREBLEControlissetlow,thesetwocontrolsbecomedominant.

Forthemostbalancedsoundandabalanceofpowerbetweenthethreerotarytonecontrols,trytousetheTREBLEControlinitsmiddleranges.Thisscenarioproducesnearlyequalrepresentationofallthefrequenciesonthetonecontrolsandprovidesagreatneutralstartingpointforfurthertweaking.

WhiletheMiniRectosEL84powersectionisnotcapableofdeliveringthemassiveamountofbassfrequenciesthatthebigRectosdowiththeir6L6powertubes,itisstillworthmentioningtousetheBASScontrolwithfinesse.ToohighaBASSsettingcancauseabloated,flubbyattackandcreateasoundthatisunbalancedandevendownrightbad.Agoodruletouseasaguidelineisthis;astheGAINisincreased,theBASSshouldbedecreased.Thehighergainsettingsaddfullnessandwarmth-andbass-allowingyoutogetawaywithlowerBASSsettings.Anotherthingthathighsettingsof

theBASSdoesistoeatupheadroom.Lowfrequenciestakemorepowertodeliveratagivenvolumethanhighfrequenciesduetotheirlongerwavelength.Yourampwillclipsoonerifthereisalargeamountofbassithastoam-plify.ThisismostnoticeableinChannel1intheCLEANModewhenlookingforcleanrhythmsounds.ThehighestheadroomisattainedforcleanchordingbykeepingtheGAINandBASSnotfarabove12:00-somewherebetween11:00and12:30.Thiswillensurethatyouarenotloadingupthefrontendwithtoomuchgainorlowendandanyclippingyouexperiencewillmostlikelycomefromthetubesreachingtheirlimitofpower.

PRESENCE ThisControlhandleshighfrequencyattenuationthatisabovethatoftheTREBLEcontrolanditslocationinthecircuitmovesdependingontheChannelandModeyouhavecalledup.InsomeModesitsaroll-offcontrolattheendofthepreamp,inothersitcontrolstheamountofnegativefeedbackatagivenfrequencyinthepowersection.Itactsindepen-

BASS

VARIABLE ACCORDING

TO TREBLE & MID CONTROL

MID

SCOOPED AND

EASY TO PLAY

ADDS PUNCH TO

WEAKER PICK-UPS


11/38

11PAGE

dentlyoftheotherrotarytonecontrolsandiscrucialinvoicingtheModes.Itisapowerfulglobaltonecontrol.LowerPRESENCEControlsettingsdarkenand,infactcompressthesignal,whichworkswelltofattensinglenotesolosounds,givingthemgirthandfocus.SomeofthebestleadsoundsinyourRectowillfindthePRESENCEControlinitslowerregionswhereabalanced,vocalresponseisachieved.

OneexampleofthiswouldbewhendialingupBluesysolosoundsintheCLEANMode.Here,itishelpfultoaddgainearlyinthepreampwiththeGAINandTREBLEsethigher(5:00&2:00)thannormalandthenrollback

thePRESENCE(9:0010:00)togetthesoundtowarmupagain.Thisschemecanberepeatedthroughoutallthemodesandalsoinreverse-wherethePRESENCEishigherandtheTREBLEisreduced.Thatsaid,manyofthebestsoundsareachievedwithbothTREBLEandPRESENCEstrayingabove12:00noononlyoccasionally,astheybothpackpowerfulfrequenciesthatcanbedangerousatthetopoftheirrange.

HighersettingsunleashthemightyroarofyourMiniRectoandproducebrighter,morepointedsoundsthatwillcutthroughamix.ThiscanbegreatforsparklingcleansoundsinChannel1andmoreaggressivecrunchrhythmsoundsinPUSHED,VINTAGEandMODERN.

MASTER Thiscontrolisthefeedfromtheendofthepre-amptothedriverstageandtheEffectsLoop.Asyoucansee,eachChannelisfittedwithitsownMASTERControl,enablingthetwochannelsrelativevolumestobematchedregardlessof

theirextremelydifferentsoundstylesandgainsignatures.TheMASTERControlmakespossibleawiderangeofsoundsthroughitsabilitytouseverylowGAINsettingsathighvolumesandconversely,highGAINsettingsatlowvolumesandeverywhereinbetween.

Again,wesuggestusingtheMASTERControlinitssensibleranges(9:00-2:00).Here,thechannelswillbeeasiertomatchwitheachotherandtheEffectsLoopwillseemorereasonablesignallevels.

NOTE:BecausetheMASTERControldeterminesthesendleveloftheEffectsLoop,extremesettingsmaycausepossibleoverloadingofFXprocessorsorpedalsInputstage,butalsomaymakebalancingthetwochannelsEffectSendleveldifficult.

STANDBY Perfectforsetbreaks...thistoggleswitchalsoservesanevenmoreimportantpurpose.Fromcold-start,theSTANDBYpositionallowsyoutowarmupthetubes-especiallypowertubes-beforeapplyingthehighvoltagebyswitchingtheStandbytotheONposition.BeforePOWERisswitchedtoON-makesuretheSTANDBYswitchisintheSTANDBYposition.

Waitatleast30secondsandthenfliptheSTANDBYswitchtotheONposition.Thispreventstheshockofhighvoltagehittingcoldtubesandreducesthelikelihoodoftubeproblemsandincreasestheirtonefullifesubstantially.

POWER ON ThisswitchdeliverstheA.C.powertotheMiniRecto.Makesuretheunitisgrounded(allthreeterminalsoftheA.C.powercordmustbeconnectedtoavoidinjurytotheuseraswellastotheunit)andthatthepropervoltageispresent.

AlwaysfollowthecoldstartproceduredescribedintheSTANDBYsectionabovewhenpoweringupyouramplifier.Thiswillreducethelikelihoodoftubeproblemsandincreasetheirmusicallife.

ThatcoverstheChannels,ModesandControlsfoundontheFrontPanelofyourMiniRecto,nowletsswingaroundtotheRearPanelandtakealookattheLoopandSpeakerOutputs.

PRESENCE

WARM

& VOCAL

BRIGHT &

AGGRESSIVE

MASTER

25 WATTS

10 W

25 W

10 WATTS

MOST SENSIBLE RANGE

EASIEST TO BALANCE CHANNELS

REASONABLE FX LOOP SIGNAL LEVELS

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


12/38

12PAGE

REST AREA


13/38

13PAGE

REAR PANEL

SPEAKERS One4Ohmandone8Ohmjackisprovidedforspeakerinterfacing.MESA/Boogiecabinetsarebuiltwiredto8Ohmsunlesscustomorderedormodifiedbyanoutsideparty(i.e.apreviouslyownedcabinet).One8Ohmcabinetshouldbeconnectedtothe8Ohmoutput.Whenusingtwo8OhmMESAcabinets,connectonecabinettothe4OhmoutputanddaisychainthesecondcabinetbycomingoutofthefirstcabinetsParalleledOutjackintothesecondcabinetsinputjack(MESAcabinetsprovideaParalleljackforthispurpose).

Ifyouareusingnon-MESAcabinetswithyourMiniRecto,itisveryimportanttoknowyourcabinetsimpedanceandmakesureyouareconnectingspeakerscorrectlyandsafelytotheamp.Failuretoconnectspeakerscorrectlycancauseexpensivedamagetotubes,transformersand

theampingeneral.ALWAYSmakesuretoconnectyourcabinetcorrectlytoyouramp.Checkouttheinformationlaterinthismanualregardingspeakerimpedanceandspeakerhook-upschemes.Nomatterhowunusualyourspeakersetup,itisgenerallypossibletogetgoodperformance.

FX LOOP YourMiniRectobenefitsfrom40yearsofhighperformanceampdesignandtheEffectsLoopfeaturedhereisaresultofthatexperienceandexpertise.TheLoopcanbeHardBypassedforpuristswhoprefernon-loopdesigns,whichremovesalltubesandcircuitryfromthesignalpath.However,eventhesetraditionalistskepticsmayhaveasurprisewhenthey,uponscrutiny,findtheyprefertheLoopActive.Ourtestshavehadthesameresults-withmostplayerspreferringtheslightaddedthree-dimensionalityandtopendenhancementandclaritythiscircuitimpartsonthesignal.

TheEffectsLoopiswiredinSerieswiththedrysignalandaslongasyouareusingprocessorsofgoodquality,youshouldexperienceseamlessinterfacingwithnotonaldegradation.Thatsaid,anythingyouinsertinthisextremelysensitivejunctionofanamplifier(betweenpreampandpowersection)mayhavethepotentialtoslightlyalterthesound.Also,everycompanythatbuildsprocessorshastheirownwayofdoingthingsandtherearecontrolsandfeaturesthatempower,andsomethatmakethingsmorecomplicatedwhileaddingquestionablesonicbenefit.Wesuggesttakingyourampandtryingitwiththeprocessoryouareauditioningtomakesureyouwillhavegreatperformancewhentheyarecoupled.

Whilemostpedal-typeeffectswillworkintheLoop,itisalwaysbesttoconnectoverdrive,distortion,boost,compressionandwahorenvelopefiltereffectsbetweentheinstrumentandtheFrontEndoftheamplifier.Theseeffectsaredesignedtoalterthesoundoftheinstrumentbeforeitisamplified,andyouwillgetbetterresultsnotusingtheLoopfortheseapplications.

AC SOCKET (Quick Disconnect Style) ThisistheACMAINSPowerCordSocket.Thestandardizedremovablepowercablesuppliedwithyourampcanonlybepluggedinoneway.Alwaysconnectthemaleendtoagroundedwallsocketwiththe

propervoltagepresent(117VoltsonU.S.A.Models).ToAvoidTheRiskOfSchock,NeverAlterThePowerCableinanyway.AlteringthePowerCablewillvoidyourwarrantyandputyouatriskwhileleavingyouramplifieropentothepossibilityofdamage.

MAIN FUSE ThisistheA.C.(AlternatingCurrent)mainfuseandprovidesamplifiercircuitprotectionfrompowerand/orrectifiertubefailureaswellasfromA.C.voltagefluctuations.ALWAYSreplaceablownfusewithoneofthespecificratingandtypeas(conveniently)printedonthebackofyouramplifierrightnexttothefuseholder.NEVERINSTALLAFUSEOFAHIGHERRATINGthanthevalueprintedonthebackofyouramplifier.Doingsowillverylikelyproducedamagewellbeyondtheoriginalreasonyourfuseblewinthefirstplace.

CAUTION:Unplug powerbefore replacingfuse

FXLOOP

HARDBYPASS

120 V~60 Hz

1 A

1 ASLOBLO

8 OHM

CAUTION: CHASSIS SURFACE MAY BE HOT! 4 OHM

SEND

RETURN

HANDBUILTINPETALUMA, CAALL TUBEAMPLIFIER

CAUTION! WARNING!

TUBE GUIDE5 x 12AX72 x EL 84

PATENTED6,621,9077,602,927

S

P

K

R

S

F

X

L

O

O

PRECT I F I ER

MIN I-TWENTY -FIV E

DYN A- WATT

FX

LOOP

HARDBYPASS

8 OHM

4 OHM

SEND

RETURN

S

P

K

R

S

F

X

L

O

OP

CAUTION:

Unplug powerbefore replacing

fuse

120 V~60 Hz

1 A

1 ASLOBLO


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14PAGE

Apowertubeshortorfailureisoftenthecauseofablownfuse.PositionyourselfbehindtheamplifierandfollowthecoldstartprocedurementionedintheSTANDBYswitchsectionofthismanual.WatchthepowertubesasyoufliptheSTANDBYtotheONposition.Ifapowertubeisgoingbadorisarcingyouwilloftenseeitasyoupowerup!FliptheSTANDBYswitchtoStandbyimmediatelyandreplacethefaultypowertubeandthefuseasnecessary.

IfyouseenothingabnormalasyoumovetheSTANDBYswitchtoON,itispossiblethatapowertubeshortedtemporarilyandcaused

theblownFuse.Occasionally,whetherfromjustluckorfromcoolingdown,ashortinapowertubereconnectsitselftemporarilyandcanoperatenormallyagainbutthistubeshouldbeconsideredfaultyandreplacedassoonaspossibletoensureuninterruptedper-formance.Ifyoucanidentifyatubethatisarcingorshortingbythemethodmentionedaboveandthetubeshaveminimaluse,considerreplacingtheobviouslyfaultyorfailedtubeandleavingtheothersinstalled.

Ifyouhaventchangedtubesforawhileafterheavieruse,thisfailuremaybetellingyouitstimetochangeallyourpowertubes.Saveanyworkingbutusedtubesasyournewspares.

Sparefuses(ofthepropertypeandrating)areamustforthefabledcordbagalongwithsparetubes.Alwayshavebothonhandatthegigorathomesincetubesdecidewhenitstimetostopworking.Sparetubesandfusescanbeworththeirweightingoldshouldyoueverexperienceatubefailure.


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15PAGE

Sample Settings #1:

TITLE: Sweet Clean (CH1) / Soulful Solo (CH2)

Sample Settings #2

TITLE: Fat Clean (CH1)/ Classic Rock (CH2)

Sample Settings #3

TITLE: Edge Clean (CH1)/ Fat Crunch (CH2)

Sample Settings #4

TITLE: Old School Cranked (CH1)/ Stinging Blues (CH2)

FACTORY SAMPLE SETTINGS

INPUT

FT SW

GAIN TREBLE MID PRESENCE MASTER

CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


16/38

16PAGE

Sample Settings #5:

TITLE: Rock Clean (CH1) / Liquid Gain Solo (CH2)

Sample Settings #6

TITLE: Tight Crunch (CH1) / Blistering Lead (CH2)

Sample Settings #7

TITLE: Punk Rhythm (CH1) / Fast Bright Lead (CH2)

Sample Settings #8

TITLE: Little Amp Cranked (CH1) / (CH2)


INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


17/38

17PAGE

Sample Settings #9:

TITLE: Rock Rhythm (CH1) / Ridiculous Gain Lead (CH2)

Sample Settings #10:

TITLE: Tight Gain Rhythm (CH1) / Lo Power Lead (CH2)


INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


18/38

18PAGE

TITLE:

TITLE:

TITLE:

TITLE:


INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

PERSONAL SAMPLE SETTINGS

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


19/38

19PAGE

TITLE:

TITLE:

TITLE:

TITLE:


INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS


POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


20/38

20PAGE

TITLE:

TITLE:

TITLE:

TITLE:


INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS

INPUT

FT SW


CLEAN

PUSHED

VINTAGE

MODERN

BASS

25 WATTS

10 W

25 W

10 WATTS


POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON

POWER

STANDBY

FT

SW

CH 1

CH 2

ON

ON


21/38

21PAGE

A

FRONTOFC

HASSIS

2

x

EL

84

MINIRECTIFIERTWENTYFIVETUBETASK

CHART


22/38

22PAGE

TUBE NOISE & MICROPHONICS Youmayoccasionallyexperiencesomeformoftubenoiseormicrophonics.Cer-tainlynocauseforalarm,thisquirkybehaviorcomeswiththeterritoryandtheTone.Muchlikechangingalightbulb,youdontneedatechniciantocurethesetypesofminoruserserviceableannoyancesandinfact,youllbeamazedathoweasyitistocuretubeproblems...bysimplyswappingoutapre-amporpowertube!

Firstmaywesuggestthatyousettheamplifieruponsomethingsothatyoucangettothetubescomfortablywithouthavingtobenddown.Italsohelpstohaveadequatelightingasyouwillneedtoseethetubesocketsclearlytoswaptubes.Usecaution

andcommonsensewhentouchingthetubesaftertheamplifierhasbeenonastheymaybeextremelyhot!Iftheyarehotandyoudontwanttowaitforthemtocooloff,trygraspingthemwitharagandalsonotethattheglassdownaroundthebulboussilverytipisconsiderablylesshotwhichmakesiteasiertohandle.Gentlyrockthetubebackandforthasyoupullitawayfromitssocket.

DIAGNOSING POWER TUBE FAILURE Therearetwomaintypesoftubefaults:shortsandnoise.Bothlargeandsmalltubesmayfallpreytoeitheroftheseproblemsbutdiagnosisandremedyisusuallysimple.

Ifafuseblows,theproblemismostlikelyashortedpowertubeandshortscaneitherbemildorsevere.Inamildlyshortedtubetheelectronflowhasovercomethecontrolgridandexcesscurrentflowstotheplate.Youwillusuallyheartheampbecomedistortedandbegintohumslightly.Ifthisoccurs,quicklylookatthepowertubesasyouswitchtheamptoSTANDBYandtrytoidentifyoneasglowingredhot.Itislikelythattwoofapairwillbeglowingsincetheshortedtubewillpulldownthebias

foritsadjacentmates,butonetubemaybeglowinghotterandthatoneistheculprit.Theothertwoareoftenfineunlesstheyvebeenglowingbrightredforseveralminutes.

Becausethereisnophysicalshortinsidethetube(justelectronsriotingoutofcontrol)merelyswitchingtoSTANDBYforafewmomentsthenbacktoONwillusuallycuretheproblem...atleasttemporarily.Watchthetubescarefullynow.Shouldtheproblemrecur,theintermittenttubewillvisiblystarttooverheatbeforetheothersandthusitcanbeidentified.Itshouldbereplacedwithonefromthesamecolorbatch,shownonitslabel.Callusandwewillsendoneouttoyou.

Thesevereshortisnotnearlysobenign.Intheworstcases,amajorarcingshortoccursbetweentheplateandthecathodewithvisiblelightninginsidetheglassandamajornoisethroughthespeaker.Ifthisisseentohappen,IMMEDIATELYturntheamptoSTANDBY.Bythistimethefuseprobablywillhaveblown.Suchashortisusuallycausedbyaphysicalbreakdowninside

thetubeincludingcontaminatecominglooseorphysicalcontact(ornearcontact)betweentheelements.Replaceitandthefusewiththeproperslo-blotypeandpoweruptheampusingthepowerupprocedureaswedescribedearlierinthismanual.

TUBE NOISE Oftencausedbycontaminationwithininatube,theculpritcanusuallybeidentified,andbylightlytappingontheglass,youwillprobablyhearthenoisechange.Hearingsomenoisethroughthespeakerswhiletappingonthe12AX7sisnormalhowever.AndtheonenearertheINPUTwillalwayssoundlouderbecauseitsoutputisbeingfurtheramplifiedbythesecond12AX7.

Thepowertubesshouldbeallbutquietwhentheyaretapped.Ifcracklingorhissingchangeswiththetapping,youhaveprob-ablyfoundtheproblem.Toconfirmanoisypowertube,merelyputtheRectoonStandby,removeitfromitssocketandturnitbackon.ItwillcausenodamagetoruntheRectobrieflywithonepowertubemissing.Youmaynoticeaslightbackgroundhum,however,asthepush-pullbecomesunbalanced.Wheneveryouaretryingtodiagnoseasuspecttube,keepyourother

handonthePOWERandSTANDBYswitchesreadytoshutthemoffinstantlyintheunlikelycaseyouprovokeamajorshort.

Ifyouthinkyouvelocatedaproblemtubebutarentsure,werecommendsubstitutingthesuspectwithanewonejusttobesureofyourdiagnoses.Youwillbedoingyourselfandusabigfavorbyjustfollowingthesimpleguidelinespreviouslymentionedregardingtubereplacement.Youllprobablybesuccessfulwithmuchlesseffortthanisrequiredtodisconnecteverythingandhaultheunittoatechnicianwhowillbasicallyperformthesamesimpletests.Ifthetubesarestillwithintheirsix-monthwar-rantyperiod,wewillhappilysendyouareplacement.Justnotethecolordesignationonthetubelabelsothatwecansendyoutheappropriatematch.


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23PAGE

DIAGNOSING PRE-AMP TUBE PROBLEMS Becauseyouramplifierisanalltubedesign,itisquitepossiblethatyouwillatsomepointexperienceminorpre-amptubenoise.Restassured-thisisnocauseforalarmandyoucantakecareoftheproblemyourselfinamatterofminutesbysimplyswappingtubes.

Letusbeginbysaying;Itisaverygoodideatokeepatleastacoupleofsparepre-amptubesonhandatalltimestoinsureuninterruptedperformance.Theseminorpre-amptubeproblemscantakemanyformsbutcangenerallybedescribedintwocategories:NoiseandMicrophonics.Noisecanbeintheformofcrackling,sputtering,whitenoise/hissand/orhum.Microphonic

problemsusuallyappearintheformofaringingorhighpitchedsquealingthatgetsworseasthegainorvolumeisincreasedthusaremorenoticeableinthehighergainHImodes.Microphonicproblemsareeasilyidentifiedbecausetheproblemisstillpresentevenwiththeinstrumentsvolumeofforunpluggedaltogether-unlikepick-upfeedbackwhichceasesastheinstru-mentisturneddown.Microphonicnoiseiscausedbymechanicalvibrationandshock:thinkofbangingamicrophonearoundandyoullunderstandwherethewordcamefrom.

Thebestwaytoapproachapre-amptubeproblemistoseeifitoccursonlyinonespecificmodeorchannel.Thisshouldleadyoutothetubeneedingreplacement.Thenallthatremainsistoswapthesuspecttubeforaknowngoodperformer.Ifyoucannotnarrowdownthetroubletoaspecificmodeorchannel,theproblemmaybethesmalltubethatdrivesthepowertubeswhichisoperationalinallmodesandchannels.Thoughrare,aproblemwiththedrivertubewouldshowupinallaspectsofperformance-soifyoucantnarrowtheproblemdowntobeingmodeorchannelspecific,youmaywanttotryreplacingthedrivertube.Driverproblemsgenerallyshowthemselvesintheformofcracklingorhuminallmodesofperformanceand/or

weakoveralloutputfromtheamplifier.Occasionallyananemicdrivertubewillcausetheamplifiertosoundflatandlifeless,butthisissomewhatuncommon,aswornpowertubesareamorelikelysuspectforthistypeofproblem.

Sometimesmakingthediagnosisismoretroublethanitsworthanditsfasterandeasiertomerelyreplacethesmallpre-amptubesONEATATIMEwithareplacementknowntobegood.ButMAKESUREyoukeepreturningthetubestotheiroriginalsocketuntilyouhittheonethatcurestheproblem.YoullnoticethattubeslocatednearertotheINPUTjackalwayssoundnoisier...butthisisbecausetheyareatthestartofthechainandtheirnoisegetsamplifiedoverandoverbythetubesthatfollow.Thetubethatgoesintothisinputsocket(usuallylabeledV1)needstobetheleastnoisyofthebunch.Thetubethatgoesattheendofthepreampchain-justaheadofthepowertubes-canbequitenoisywithoutcausinganyproblematall.ThetubesinyouramphavealreadybeenlocatedinthemostappropriatesocketsandthisiswhyyoushouldNEVERpullthemalloutatonceandALWAYSswapthemoneatatime.ALWAYSreturnaperfectlygoodtubetoitsoriginalsocket.AlsoitsagoodideatoputtheamponSTANDBYwhenswappingtubestoreducetheheatbuildupinthetubesthemselvesandtopreventexplosive

noises(whichcanstilloccurevenifyouarepullingthetubesawayfromtheirsocketsgently)fromcomingthroughthespeaker.

Remember,takeyourtime,bepatientandchancesarerealgoodthatyoucanfixyourampyourselfbyfindingandreplacingthebadtube.Itkillsustoseesomeonewhohasshippedtheirampbacktous...andallitneededwasasimpletubereplacement!Ifyoumustsendbackyouramp,removethechassisfromthecabinetbyunscrewingthefourmountingboltsonthebottomtop.Thechassisthenslidesback likeadrawerandcomesoutfromtheback.Removethebigpowertubesandmarkthemaccordingtotheirlocationfromlefttoright1,2etc.Theyneedtobewrappedseparatelywithplentyofwaddedupnewspaperaroundthemandputinasmallerboxwithinthelargercarton.RemovetheRectifiertubesandwrapthemalso.Youcanleavethepreamptubesinorremovethemandwrapthemseparatelybeingsuretolabeltheirlocation.(SeeTubeTaskChart.)

Towrapthechassis,useplentyoftightlywaddedupnewspapersothereisatleastsixinchesofcrushspacebetweenthe

chassisandthecardboardbox.Bubblewrapalsoworkswell,butpleaseDONTusestyrenepeanuts-theywillshiftduringtransitandgetlodgedinsideyourelectronicsaswellasallowingyouramptoendupatthebottomoftheboxunprotectedandpossiblydamaged.

Pre-amptubesdontnormallywearoutasarule.Therefore,itisnotagoodideatochangethemjustforthesakeofchangingthem.Ifthereisntaproblem-dontfixit.Ifthereisnoresultfromyoursubstitutions,itmaybepossiblethatyouhavemorethanoneproblematictube.Thoughrare,thisdoeshappenandthoughitmakesthetroubleshootingprocessalittlemoreintimidating,itisstillpossibletocuretheproblemyourself.

NOTE:Itisnormaltohearaslightmetallicringingsoundwhentappingonthepreamptubes.Aslongasthetubedoesnotbreakintooscillationorstartcracklingoranyotherformofbizarrenoise,itisconsiderednormalandfunctional.


24/38

24PAGE

IMPEDANCE Wiringupspeakerstoprovidethemosteffectiveloadandmakingsurethatallofthemareinphasewillhelpincreatingthebestsoundpossible.Thisisnottoodifficult,aslongasyouunderstandafewthingsaboutloadingandhowtoconnectyourspeakerstoprovideanoptimalresistiveload.

MESA/Boogieamplifierscanhandle4and8ohmseffectively.Neverrunbelow4ohmsinatubeamplifierunlessyouareabsolutelycertainthatthesystemcanhandleitproperly;thiscancausedamagetotheOutputtransformer.Afewamplifierscanhandle2ohmseffectivelywithoutdamagingthem(forexampletheMESAsBass400+).Youcanalwayshaveahigherresistance(16ohms,forexample)withoutdamagingresults,buttoolowofaresistancewilllikelycauseproblems.

MIS-MATCHING: Whenrunningahigherresistance(forexample:8ohmoutputinto16ohmcabinet),aslightlydifferentfeelandresponsewillbeeminent.Aslightmismatchcanprovideadarkersmoothertonewithalittlelessoutputandattack.Thisresponseisaresultoftheamplifierrunningabitcooler.Sometimeswhenusingmorethanonecabinetamismatchwillbetheonlyoption.

WHAT IS MY CABINETS IMPEDANCE? Ifyouhaveonlyasinglespeaker,youjustmatchthatsinglespeakersimpedance

totheamplifier,andyouaredone.Inmanycases,youwillhaveanumberofspeakers,andthenyoumustcalculatetheloadthattheamplifierwillneedtosupport.Therearegenerallythreewaystowiremultiplespeakerstogether.Theyareasfollows:

SERIES: Whenyouwire(hook-up)speakersinSeries,thespeakersresistance(asmeasuredinohms)isadditive-i.e.puttingtwo8ohmspeakersinSeriesresultsina16ohmload.

Speaker A = 8 Ohms Speaker B = 8 Ohms

SERIES: Connect the Negative side of Speaker Ato the Positive side of Speaker B

POSITIVE = NEGATIVE =

BLACK

SHADOW

BLACK

SHADOW

SPEAKER IMPEDANCE MATCHING & HOOK-UP GUIDE:


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25PAGE

PARALLEL: Whenwiringinparallel,theresistanceofthespeakersdecreases.Two8ohmspeakerswiredin(hooked-up)Parallelresultsina4ohmload.Itseasytocalculatetheeffectofaresistiveloadwhenallthespeakersareallthesameresistance.ItisreallynotsuggestedtowiredifferentresistiveloadvaluesinParallel(8and4,16and8etc.)TheformulaforfiguringthetotalimpedanceinParallelisthemultiplicationofthetwoloadsdividedbythesumofthetwoloads-i.e.putting

two8ohmspeakersinParallelresultsina4ohmload.ConnectthePositivesideofSpeakerAtothePositivesideofSpeakerB-ConnecttheNegativesideofSpeakerAtotheNegativesideofSpeakerB.

COMBINATION OF SERIES & PARALLEL: ThisisreallyjusttwosetsofSerieswiredspeakerscon-nectedinParallel.Thisishowyoumaintainaconsistentloadwithmultiplespeakers.Theimportanceofthisismoreevidentwhenyouhavemorethanonecabinettoconnecttoyouramplifier.Thisiswhenyouneedtofigureouttheloadsandhowtowirethemupwithoutapplyingtoolowofaresistanceontheamplifier.

SimplyconnectthePositivesideofSpeakerAtothePositivesideofSpeakerC.

ConnecttheNegativesideofSpeakerAtothePositivesideofSpeakerB.Next,connecttheNegativesideofSpeakerCtothePositivesideofSpeakerD.

Andlastly,connecttheNegativesideofSpeakerBtotheNegativesideofSpeakerD.

4Eight(8)OhmspeakerswiredinSeriesParallel=

POSITIVE

Speaker A

8 Ohms

Speaker B

8 Ohms

NEGATIVE

Total Load = 4 Ohms

BLACK

SHADOW

BLACK

SHADOW

SPEAKER A SPEAKER B

SPEAKER C SPEAKER D

NEGATIVE

POSITIVE

BLACKSHADO

WBLACKSHADO

W

BLACK

SHADOW B

LACK

SHADOW

SPEAKER IMPEDANCE MATCHING & HOOK-UP GUIDE: (Continued)


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26PAGE

WIRING SCHEMES...Amplifier to Speaker Cabinets

8 OHM 4 OHM

Partial back view of amplifier

4 Ohm Cabinet

2

8 OHM 4 OHM

Partial back view of a Mesa amp

8 Ohm Cabinet

SAFE MISMATCH

3

8 Ohm Cabinet

8 OHM 4 OHM

Partial back view of amplifier1

8 OHM 4 OHM


16 Ohm Cabinet

SAFE MISMATCH

4


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27PAGE

8 OHM


SERIES BOX

8 Ohm

4 Ohm 4 Ohm

4 OHM 8 OHM


PARALLEL BOX

8 Ohm

16 Ohm 16 Ohm

16 Ohm Cabinet 16 Ohm Cabinet

4 OHM


CORRECT

MATCHCORRECT

MATCH

76


5


4 OHM 8 OHM


SAFE MISMATCH

NOTE:BothSeriesandParallelboxesmaybepurchasedthroughMesa/BoogiebycontactingCustomerService:707-778-6565,Mon-Thurs9am-5pmPST


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28PAGE

4 OHM 8 OHM



SERIES BOX16 Ohm

8 Ohm 8 Ohm

8 Ohm Cabinet

SAFE MISMATCH


8

4 OHM8 OHM



PARALLEL BOX8 Ohm

16 Ohm 16 Ohm

16 Ohm Cabinet

SAFE MISMATCH

9

NOTE:BothSeriesandParallelboxesmaybepurchasedthroughMesa/BoogiebycontactingCustomerService:707-778-6565,Mon-Thurs9am-5pmPST


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29PAGE

AFeatureArticlebyRandallSmithHeresaquestionweoftenhear:

Why doesnt MESA put bias adjustments in their amplifiers?

Well,theresashortanswerandalonganswertothisquestion.

Theshortansweristhatduringmy12yearsofrepairingFenders,oneofthemostfrequentproblemsIsawwasbiascontrolsthatwereeithersetwrongorthathadwanderedoutofadjustmentduetovibration.Asanyhonesttechwilltellyou,thereslotsofeasymoneytobemadebysprinklingholywateronamplifiers...uh,whatImeanttosayisYourampneededbiasing.SeewhatImean?Whatcustomerisgoingtoarguewiththat?

Itonlytakesamomentandavoltmeter:TheFenderdiagramshowshow:Adjustthistrimpotfor-52volts.Thatsit.Noth-ingmore.

Nowdontbefooledintothinkingthattubesdrawmoreorlessbias,theydont.Thewayabiassupplyisconnectedtoatubeisakintoadeadendroad,itjusttrailsofftonowherewithoutreallycompletingacircuit.Itsastaticvoltageandregardlessofwhattubeisinthesocketorevenifthetubesarentpluggedinatall,itdoesntchangethebiasvoltageabit.

Sotheendoftheshortansweristhis:Sinceabiassupplyneedstoputouttherightvoltageandnevervary,IwantedtobuildamplifiersthatwereindividuallyhardwiredtothecorrectvaluesandNEVERneededadjustment.Andfor25years,thatshowMESA/Boogieshavebeenbuilt.

Timetochangetubes?JustplugourtubesintoanyoneofourampsandyoureDONE.Notechneeded.NObillsandnoBSaboutbiasing.Andmostimportant:ThebiasisRIGHTbecauseitcantchange!

Now,youwantthelonganswer?Heresmoreinformationonhowourhard-wiredbiasavoidstrouble.Pleasereadon.

Butfirst,letsmakeanimportantdistinction.Ourbusinessisdesigningandbuildinghighperformanceamplifiers.Andforthisweneedtubeswhosevarianceiswithinanarrowrange.Ourwarehouseisfullofrejects...oh,theyworktheyjustdontperformwithinourtolerancerange.Wehaveaverysophisticatedcomputer-basedtubetestingsystem(nicknamedRobotube)thatmatchesandmeasurestubesoversevenimportantparameters.Itcanevenpredictwhichtubesarelikelytohaveashortenedlifetimeeventhoughtheyworkperfectlyduringthetest.

Becauseourbusinessisbuildingqualityamps,wecanaffordtorejectalotofwaywardtubes.TheguysyouhearcomplainingbecauseBoogiesdonthavebiasadjustersareprimarilyinthebusinessofsellingtubes-notamps.Theydontwanttothrowaway30percentoftheirinventory,sotheypromotetheideathattubesoutsideourparameterscanbeusedtocustomizeamplifiersandtheycriticizeusbecauseourampscantbeadjustedtoaccommodatetheirout-of-MESAtolerancetubes.

Nowyoumightbethinking,ButIthoughtyoujustsaidthattubesdontdrawbias,thereforetheydonteffectthebiassupplyandthusitdoesntneedtobeadjustable.

Whenyousetthebias(whetheritsbyselectingtherightresistors,aswedo,oradjustingatrimmerwhichisquicker)whatyouaredoingisestablishingthecorrectamountofidleCURRENTthatflowsthroughthepowertubes.Butyoucantadjustthecurrentdirectly,youcanonlychangeitbyadjustingtheamountofbiasVOLTAGEthatgoesontothetubescontrolgrids.

VoltageandcurrentareNOTthesame.CurrentistheAMOUNTofelectricity,thequantityandismeasuredinamperes.Voltageis thedegreeofelectricchargelikethepressuretousetheoldwateranalogy.Letmeillustratehowdifferent

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PLATE

Structure of a 6L6 / 5881

Beam Power Pentode.

BEAM-

CONFINING

ELECTRODE

SCREENGRID

GRID

CATHODE

BIAS ADJUSTMENT


30/38

30PAGE

voltageandcurrentare:Whenyouscrapeyourfeetacrossacarpetedfloorindry,winteryconditions,yourbodycanbecomechargedwith50,000to100,000voltsofstaticelectricity.Andwhenyoureachforthedoorknob,asparkjumpsandyoufeelit!Thevoltageissuperhighbutthecurrent(measuredinmicro-amps)istiny-otherwiseyouwoulddiefromelectrocution.

Contrastthiswithyourcarbattery,whichputsoutamere12volts.Youcanlayyourhandsrightacrosstheterminalsandnot

feelathing.Yettheamountofcurrentavailablecanruntoseveralhundredamperes..enoughtoturnoveracoldengineandgetitstarted.

Socurrentandvoltagearetwototallyseparateelectricalparametersthoughwhenyoumultiplythemtogether,yougetPOWER,whichismeasuredinwatts.

Whenyousetthebiasofanamplifier,youareadjustingthestaticVOLTAGEatthecontrolgridofthetubeinordertoproduceadesiredamountofidleCURRENTflowingtothetubesplate.Asmallchangeingridvoltage,producesalargechangeintheamountofcurrentflowingandthatsbasicallyhowatubeworks.Saythatagainbecauseitssuperimportant:Asmallchangeinvoltageatthegridcausesalargechangeincurrentflowingtotheplate.See,thatstheessenceofamplification:Asmallchangecausingalargechange.Andhereitsasmallvoltagechangecausingalargecurrentchange.

Thebiasconditionsarewhatdetermineshowmuchcurrentflowsthroughthebigpowertubeswhenyourenotplaying.AndwhatdrivesyourspeakersisfluctuationsinthatcurrentflowwhenyouAREplaying.Iftheamountofcurrentincreasesanddecreases440timespersecond,thenyoullhearanAnote.Ifthefluctuationsincurrentflowarelargeandstillat440persecond,youllhearanAthatisLOUD!

Butforpurposesofbiasing,itstheamountofplatecurrentflowingwithnosignalappliedthatsimportant.Unfortunatelycurrentishardtomeasurebecausethecircuitmustbeinterruptedasincutthewireandthemetersplicedinserieswiththebrokencircuit.ButmeasuringVOLTAGEiseasy.ItisnotnecessarytointerruptthecircuitbecauseavoltagereadingcanbetakeninPARALLELwiththecircuitintact.

Thus,asamatterofconvenience,mostbiassettingsaregiveninvoltsatthegrid...eventhoughcurrentthroughtheplateistheimportantfactor.Infactplatecurrentissoinconvenient(anddangerous)tomeasurethatFenderdoesntevenstatewhatthecorrectvalueshouldbe.Theyonlygivethegridvoltagethatwillproducethatcurrent.(Thatstheminus52.)Butthatonlyhappensifthetubesbeingusedareinspec.

AslongasthetubesAREinspec,therightbiasvoltagewillalwaysgivethecorrectplateCURRENTbutthentheresnoneedforthebiasvoltagetobeadjustable!

IfthetubesareNOTinspec,thentheonlyproperwaytore-setthebiasistocutthecircuitandmeasurethecurrentwhileadjustingthebias...butnomanufacturerIknowevenSTATESthedesiredcurrentvalue!Bethatasitmay,whentheoriginalbiasvoltageisalteredfarenough,itwillcompensateforthetubesabnormalperformanceandthecorrectamountofidlecur-rentflowmaythenberestored.Clearlythisissomethingmostrepairtechsshouldnotattempt.

SomenewerampshaveLEDindicatorsconnectedtothecircuitwhichwillturnonwhentherightthresholdofcurrentflowhasbeenreached.Thisisanimprovement,andalmostworthyifyourewillingtoacceptresistorsandlightsaddedintoyouramplifiersaudiopathwhichwearent.

Theotheradvantageof thissystemisthatitallowssomeampmanufacturerstoavoidmatchingtheirpowertubes.Thethinkingisthatadjustingthebiastoeachtubeseparatelyeradicatestheinherentdifferencesbetweenthetubesbyinsuringthatthesamecurrentflowsthrougheachone.

Again,thishassomemerit..butitsstillnotasgoodasusingtubesthatarematchedinthefirstplacebecausecompensatingforthemis-matchcausesthepush-pullcircuititselftobecomeunbalanced.Twowrongsdontreallymakearight.

BIAS ADJUSTMENT (Continued)


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31PAGE

Someoftheotherrecommendedbiasing,methodssuchas-..tubesrunningredhot,increasethebias..soundsharshandrunstoocool,turnitdown...areguessworkatbest.Luckily,oneofthegreatthingsabouttubeampsisthattheycanusuallystandsomeabusewithoutcausinganyrealharm...atleastnotimmediately.Butdontthesealterationsimplythatyouaresecond-guessingtheampdesignerandthattheresabettersetofoperatingconditionsthatthedesignermissedbutthetubesellershavediscovered?

Nowsomeplayersmaylikethesoundoftheirampalteredbytubeswithextremecharacteristicsandwiththebiassettohelpcompensate.Butoftenitisthemerenoveltyofchangethattheyrereallyrespondingtoandwhentheampgoesbacktotheproperoriginalway,weveseenthembefarhappierstill!

Becauseeverypartineveryoneofourdesignshasbeenmeticulouslyevaluated,comparedandstressedovernomatterhowseeminglyinsignificantitmightbe.Andwitheverydesignwelookforasweetspotwherealltheparametersincludingthebiascometogethertogivethebestsonicperformance,consistentlyandreliably.Everypartandvoltageisimportantyetnoonecomplainsthattheseotherparametersarentavailablefortinkering.

ConsiderourpatentedSimul-Classcircuitrywheretherearetwodifferentbiasvoltagesusedforseparatepairsofpowertubes...andchangingonevoltagealsochangestheother.Greatcaregoesintogettingthisjustrightandwethinkwedbeaskingfor

troubletohaveitadjustablefortheworldtoplaywith...unlessyoulikepayingtohaveyourampmessedup.Sorry,Imeanttosay,Uh,...yourampneededbiasing.

Ifthatdoesntappealtoyou,thenmerelyplugamatchedsetofMESAtubesintooneofourampsandyourereadyfortone.Guaranteed.Youdbeamazedatthenumberofservicecallswefieldeverydaythatleadtoadiagnosisofout-of-tolerance,non-spectubeproblems.Tothinkthesewouldbepreventedbyincludingabiasadjustmentissomethingofaninsulttoyouandus.Ifyouputthewrongsizetiresonyourcar,doyouthinkchangingthepressurewillmakethemright?

Please,dontthinkthisisablanketindictmentoftheotherguyssellingtubesitisnt.Andtheirtubesarentallbadeither.ItjustdoesntmakesensetopaymoreofyourhardearnedcashfortubesthatwereprobablymadeinthesameRussianorChinesefactoryandwhichhavethepossibilityofbeingoutsidetheperformancewindowweselectforyouramp.Anditpainsustohearthehypeandmystiquebuiltuparoundbiasingwhentwenty-fiveyearsofevidenceaffirmsourdecisiontomakebias

circuitsthatneverneedadjustment.HowmuchmoneyandtroublethathassavedMESA/Boogieplayersyoucouldntestimate.

OurrigorouslytestedandhandselectedtubesareavailableatyournearestMESA/BoogieProCenterorfromusdirectly.Nobodyoffersbetterprice,qualityorwarrantythanwedo...sowhyswerve?

Cheers!

RandallSmithDesigner&President

MESA/BoogieLtd.

BIAS ADJUSTMENT (Continued)


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32PAGE

WithapologiestoFriendsandRelativesfromtheEmeraldIsle-whowillmaketheirappearancesoonenough-thehumorwhichfollowsisdedicatedtothememoriesofSpecMcAuliffandFae(Rafael)McNally,twooftheTrueGreats.

Astheirnumericalreferencessuggest,thetermsDiode,TriodeandPentodeindicatethenumberofelementswithinthevacuumtubei.e.two,threeorfive.Alltubesalsorequireafilamentorheaterwhichisnotincludedinthecount.Itspurposeistoexciteelectronsfromthecathodecoatingbyraisingthetemperaturesuchthattheyareabletoboiloutoftheelectron-richcoatingmaterialandformacloudoffreeelectronsinthevacuumspacesurroundingthecathode.

Althoughthetermfilamentandheaterareoftenusedinterchangeably,therearespecificdifferences:A filamentisadirectlyheatedcathodewherecathodecoatingisapplieddirectlytotheheatingelement.Examplesare5U4twindioderectifierand300Btriodeamplifiertubes.Aheater,ontheotherhand,isaheatingelementwhichisseparatefromthecathodeandisusuallyinsertedwithinthetubularcathodesleeve.Examplesare12AX7twintriodeamplifierand6V6orEL84beampowerpentodetubes.Inallcasesthisfundamentalaspectofeachtubesconstructionisclearlyvisible,especiallywhentheheatingelementisglowingredhot.

Thecathode,then,wouldbeconsideredthefirstnumberedelementbecauseitisthesourceoftheelectrons.TheworditselfisfromtheGreekliterallymeaningcompletelydown,whichimpliesasenseofcentralorigin-likethecenteroftheearthwhereTonebegins.Itmightbesaidthatanecstaticaudiophileexperiencesapositivecatharsis,hissoulbeingpurifiedwhenhissystemtransportshimtoAudioNirvana.Theonlytroublewithtakingthispositiveimagerytoofaristhatthecathodeis,unfortunately,negative...atleastelectricallyspeaking.Howeverthisiseasilyrememberedsincevirtuallyallmusiciansandaudiophileshavealsoexperiencedthemorecommonnegativecatharsiswhentheyemergefromtheemotionalrebirthkickingandscreaminginrageandfrustration.

Onceheated,theintrinsicallynegativeelectronsareenergeticlittlefellowsofalmostnomass.Thustheymaybeacceleratedalmostinstantaneouslyandwilltravelthroughavacuumanearlythespeedoflight.Beingoflike,negativecharge,theytendto

repeloneanotherandthuswithintheelectroncloudsurroundingthecathode,thereismuchjostlingandelbowingaseachonetriestomaintainhisdistancefromalltheothers...unlessthereisastronganduniversalattractionfromanoutsideinfluence.

Visualize,ifyouwill,agroupofsub-atomicIrishmenmillingaboutandinarepellent,negativestateofmind.Allarescowlingandnonewantstohaveanythingtodowiththeother.Nowintroduceastrongattractionsay,apublicbar,andyoucaneasilypictureanorderly,ifrapidmovementofthelotinasingledirection.Thisiswhathappenswhenapositivelychargedelementcalledtheanodeorplateisintroducedintothevacuum.

Theplateisthelargemetalelementmostprominentlyvisiblethroughtheglassofanelectrontube.Itistheoutermostelementofatubesstructureanditsurroundsalltheothers.Thecathodeisatthecenterradiatingelectronsoutwards.Ashigherandhigherpositivevoltageisappliedtotheplate,theattractionfortheelectronssurroundingthecathodeisincreasedandwithnoth-ingstandingintheway,fulluninhibitedflowtotheplateoccurs...sortoflikeremovingthedoorsandofferingfreedrinkstothe

crowdofsurlyIrishmenmillingaroundoutside.Aselectronsflowtotheplate,thespacechargewillcontinuallybereplenishedbyfurtherboilingofthehot,electron-richcathodeasyoucaneasilyimagineotherIrishmenimpatientlytakinguptheplacesofthosewhovegoneinside-untiltheentirevillageisdeserted.

Now,wheredotheycomefromandhowdotheyemerge?Well,agrandandelegantladyonceshowedmehowtoreviveflatchampagne:Shedroppedaraisinintotheglass.Therewasadramaticandimmediateincreaseineffervescencewiththeintroductionofacathodingsurface.Thousandsoftinybubblessuddenlyappeared-andcontinuedtoflowfromtheraisin.Ofcoursethebubblesweremadeupofgasdissolvedinthebeverage,buttheanalogymakesiteasytovisualizethelooselyboundelectronsdissolvedintherichcathodecoatingastheyeffervescefromitsheatedsurface.

ON TRIODES, PENTODES & IRISHMEN:

ALookIntoTheInnerWorkingsoftheVacuumTube:AFeatureArticlebyRandallSmith


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33PAGE

Butbacktotheelectronflow.Iftheelectronsarestronglyattractedtoapositivelychargedplate,thenitfollowsthattheyarestronglyrepelledbyanegativelychargedplateandtheyare.Thus,ifanalternatingcurrent-suchascomesfromatransformer-isappliedtotheplate,electronswillflowonlyduringthetimeswhentheplateispositivelycharged.Duringperiodsofnegativeplatecharge,electronflowisstoppedandthespacechargeofelectronsremainscompressedintheareaaroundthecathode.

Thusadiodetube-onewithacathodeandananode-ismostlyusedtorectifyalternatingcurrentintodirectcurrentbypass-ingitwithoutrestriction,butinonedirectiononly.ThisalsoexplainswhyclosingtimeisstrictlyenforcedatIrishpubs:Duringnormaloperation,thetrafficflowissimilarlyunimpededanduni-directionaltowardthebarandthisprocessrectifiesthework-daynegativity.Itgoeswithoutsayingthatnooneleavesaslongastheatmospherearoundthebarremainspositivelycharged.

TRIODES ThissectionisacontinuingtechnicaltreatiseontheworkingsofIrishPubsbuttomakeiteasierforthelaymantounderstand,itisexplainedintermsofvacuumtubetechnology.Entertheoriginalbar-freebeerandnodoors.Well,itturnsoutthatsomecontrolovertheflowcanbeanecessaryandusefuladvantage.Thisledtotheinventionofthoseswinginglou-veredsaloondoorswhichareopenatthetopandbottom.Theyarepatternedafterthecontrolgridofthevacuumtube,whichisalooselywoundcoilofthinwirelocatedbetweenthecathodeandtheplate.

InaTriodetheplateisalwayspositivelychargedwithhighvoltageD.C.andeventhoughthegridisblockingthepath,thosenegativeelectronscanstillFEELthestrongattraction-justastheIrishmencanseeinthroughthelouversofthebardoors.Theyknowwhatpleasuresliebeyond,buttogetthererequiresovercomingthenegativeinfluencescontrollingtheaccess.ThisnegativeinfluenceistypicallycalledaBias.InelectronictermsthatmeansthegridissuppliedwithavoltagewhichisslightlyMORENEGATIVEthanthealreadynegativeelectrons.ThemorenegativetheBias,themoreittendstoneutralizetheattractionoftheplateandrepeltheelectronsbacktowardthecathode.

TheIrishcanbesimilarlychargedwithBias,butunlessyouareIrishyourself,thistypeofBiasingmaybemoredifficulttounderstand.Theeffectissimilarthough:ThemorenegativetheBias,themoreitimpedesforwardprogress.Generallyspeak-ingthough,theelectronicBiasofthegridiseasiertoovercome,andfortwomainreasons:First,theBiasisset-likethebardoors-toallowsomepassage.Second,thegridismostlyNOTTHERE,likethelouvereddoorswhicharemostlyopenspaces.Unliketheplatewhichissolid,thegridislikeacoiledbedspring.Itcancreatearepellingfieldbutmostlyitsemptyspacein

betweenwidelyseparatedwindingsofwire.Itsveryeasytocontroltheelectronsastheypassthroughthegridsforcefield:Changingthegridvoltageonlyslightlywillhaveanenormouseffectonhowmuchcurrentflowsthrough...andthatswhatAMPLIFICATIONis:asmallchangeinvoltageatthegridcausingalargechangeincurrentflowingtotheplate.

Thepurposeofthelouveredbardoorsissimilartothatofthegrid,namely,togivemomentarypausewhilestillrevealingthepromisewithin.Hesitationmostlygiveswaytotemptation,buttherearethosefewstalwartIrishmenwhothinktwiceandde-cidetocomebacklater.Mostjustpauseslightlythengoonthrough.Thatisthepurposeofthebardoors:topreventeveryonefromcrowdinginallatonce-andasthedoorismadelessofabarrier,widerspacesbetweenthelouvers,moreofthebarsattractiveinfluenceisfeltoutsidethusamplifyingthecustomerflowandincreasingthecrowdatthebar.

PENTODES Occasionallythough,bardoors-eventhelouveredtype-werefoundtobetooeffective,andtoomanycus-tomersturnedaway.Somethingfurtherwasneededtoincreasetheattractionofthebarandovercometheresistancecreated

bythedoor.Thusthecocktailwaitresswasinvented.

Onceagaintheideawasinspiredbythevacuumtube.Ithadbeendiscoveredinsometubes,oftenlargepowertypes,thatthedistancetotheplatewastoogreattoattractenoughelectronspastthenegativeinfluenceofthecontrolgrid.Soanothergridcoiloffinewirewasinsertedbetweenthefirstgridandtheplate.Thiswascalledthescreengridandcarryingahighlypositivecharge,itfunctionedasabaitfortheplate.

InaproperlydesignedpowertubesuchasanEL84ora6V6,thewindingsofthescreengridarepreciselyalignedtofallintheshadowofthecontrolgrid.Thiswaytheelectronsrespondingtothepullofthescreengridarelinedupinsheetsastheypassbetweenwindingsoftheinnercontrolgrid...onlytofindthattheyhavebeenfooled!Oncepastthecontrolgridanddrawntoward

ON TRIODES, PENTODES & IRISHMEN: (Continued)


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34PAGE

ON TRIODES, PENTODES & IRISHMEN: (Continued)

thescreengrid,theydiscover...theresalmostnothingthere.ThepaththeyreonhasthemalignedtozingstraightthroughthespacesBETWEENscreengridwindings.Soratherthanacloseandpersonalencounter,theyjustflyonpast-andoncetheyreoutthatfar,theresnostoppingthem.Theinfluenceoftheplatetakesoverand-beingsolidmetalandofthehighestpositiveattraction-itisatthisfinaldestinationthattheelectronscongregate.

Thusthepropercocktailwaitress-visiblethroughthelouvers-isscantilycladsoastobeallthemoreeffectiveatreinforcingtheattractiveinfluenceofherbarandbybeinglocatedinbetweenthedoorandthebar,sheservesasbaittolurecustomerspastthedoorsnegativeinfluence.Oncethroughthedoorhowever,itistherareIrishmanwhoactuallycomesinpersonalcon-tactwiththecocktailwaitressas,forallintentsandpurposes,she-likethescreengrid-turnsouttobeavanishingillusion.Yet,havingcomethisfar,thesolidinfluenceofthebaritselfnowtakesoverandattractsthecustomerstocongregate,havinghappilyreachedtheirdestination.

Ifyourestillfollowingthisandhaventlosttrackofthecount,youllknowwerestilloneelementshortofthefiveneededtomakeaPentode.Thislastpartisapairofbeam-confiningshieldswhichbeingnegativelycharged,servetodirecttheflowrighttowardtheplate.This ismuchthewayashor tentrancehalltothebarpreventswanderingaccidentallyintotheMensroomontheway.

Onceatthebarthough,thecircuitiscompleteandtheprocessofsoul-nourishingworksitsritualmagic.Biaseshavingbeenovercome,illusorynightingaleshavingvanished,thespiritstrulysoarandtheoncesurlyIrishmennowarefilledwithwarmth,witandkindredfriendship,enjoyingthemusicandglowingnicelywiththeirheaterson.

WithappreciativethankstotheinhabitantsoftheLandoftheLeprechaun,wehavenowconcludedourlittlediversionintothemechanicsofproperbarlay-out.

RandallSmithDesigner/President

MESA/BoogieLtd.


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35PAGE

PARTS

CHART:MINIRECTIFIERTwenty-FiveHead,Front

PARTS

CHART:MINIRECTIFIERTwenty-FiveHead,Back

INPUT

FTSW

GAIN

TREBLE

MID

PRESENCE

MASTER

POWER

STANDBY

CLEAN

PUSHED

VINTAGE

FTSW

CH1

CH2

MODERN

25WATTS

10W

ON

ON

MINIRECTIFIER25-Front

BASS

25W

10WATTS

MI

NI

TWENTY~FIVE

600631

SWITCH

pt#

600631

SWITCH

pt#

408300

ALLFRONTPANELKNO

BS

pt#

POT#

590792

POT#

590150

SWITCH

pt#607231

SWITCH

pt#

607231

SWITCH

pt#607231

JACK

pt#619112

JACK

pt#619112

SWITCH

pt#607231

POT#

59073

9

POT#

590148

POT#

59079

4

POT#

590738

POT#

590737

POT#

590148

POT#

592596

POT#

590739

POT#

590738

POT#

590736

3POS

SWITCH

pt#6

07233

394232

CH1LEDGRN

pt

#394201

CH2LEDRED

pt

#

CAUTION:

Unplugpower

beforereplacing

fuse

FX

LOOP

HARD

BYPASS

120V~

60Hz

1A

1A

SLO

BLO

8OHM

CAUTION:CHASSISSURFACEMAYBEHOT!

4OHM

SEND

RETURN

HANDBUILT

INPETALUMA,CA

ALLTUBEAMPLIFIER

CAUTION!

WARNING!

TUBEGUIDE

5x12AX7

2xEL84

PATENTED

6,621,907

7,602,927

S P K R S

F X

L O O P

RECTIFIER

MINI-TWENTY-FIVE

DYNA-WATT

MINIRECTIFIER25-Back

ACRECEPTACLE

pt#613714

SWITCH

pt#607200

DOMEST

ICFUSE

HOLDER

pt#790347

EXPORT

FUSE

HOLDER

pt#

790346

FUSEEXPORT

pt#

795205.5

A

FUSEDOMESTIC

pt#7901011A

ALLJACKS

pt#

619357


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Tank you or trusting MESA/Boogie to be YOUR amplier company.

We ish you many years o toneul enjoyment fom this handbuilt, all tube instrument.


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CustomerService

707.778.6565Fax 707.756.1503

1317RossStreet.Petaluma .CA94954.USA

minirecto25 usermanual

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