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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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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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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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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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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
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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
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REST AREA
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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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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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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
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
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
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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)
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
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
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
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Sample Settings #9:
TITLE: Rock Rhythm (CH1) / Ridiculous Gain Lead (CH2)
Sample Settings #10:
TITLE: Tight Gain Rhythm (CH1) / Lo Power Lead (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
GAIN TREBLE MID PRESENCE MASTER
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
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TITLE:
TITLE:
TITLE:
TITLE:
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
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
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
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TITLE:
TITLE:
TITLE:
TITLE:
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
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
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
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TITLE:
TITLE:
TITLE:
TITLE:
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
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
CLEAN
PUSHED
VINTAGE
MODERN
BASS
25 WATTS
10 W
25 W
10 WATTS
INPUT
FT SW
GAIN TREBLE MID PRESENCE MASTER
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
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A
FRONTOFC
HASSIS
2
x
EL
84
MINIRECTIFIERTWENTYFIVETUBETASK
CHART
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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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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.
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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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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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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
Partial back view of amplifier
16 Ohm Cabinet
SAFE MISMATCH
4
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8 OHM
Partial back view of amplifier
SERIES BOX
8 Ohm
4 Ohm 4 Ohm
4 OHM 8 OHM
Partial back view of amplifier
PARALLEL BOX
8 Ohm
16 Ohm 16 Ohm
16 Ohm Cabinet 16 Ohm Cabinet
4 OHM
WIRING SCHEMES...Amplifier to Speaker Cabinets
CORRECT
MATCHCORRECT
MATCH
76
4 Ohm Cabinet 4 Ohm Cabinet
5
8 Ohm Cabinet 16 Ohm Cabinet
4 OHM 8 OHM
Partial back view of amplifier
SAFE MISMATCH
NOTE:BothSeriesandParallelboxesmaybepurchasedthroughMesa/BoogiebycontactingCustomerService:707-778-6565,Mon-Thurs9am-5pmPST
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4 OHM 8 OHM
Partial back view of amplifier
8 Ohm Cabinet 8 Ohm Cabinet
SERIES BOX16 Ohm
8 Ohm 8 Ohm
8 Ohm Cabinet
SAFE MISMATCH
WIRING SCHEMES...Amplifier to Speaker Cabinets
8
4 OHM8 OHM
Partial back view of amplifier
16 Ohm Cabinet 16 Ohm Cabinet
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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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
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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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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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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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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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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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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
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