Mesa/Boogie Mini Rectifier Twenty-Five User Manual

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DIAGNOSING PRE-AMP TUBE PROBLEMS
Becauseyouramplifierisanalltubedesign,itisquitepossiblethat
youwillatsomepointexperienceminorpre-amptubenoise.Restassured-thisisnocauseforalarmandyoucantakecare
oftheproblemyourselfinamatterofminutesbysimplyswappingtubes.
Letusbeginbysaying;Itisa“verygood”ideatokeepatleastacoupleofsparepre-amptubesonhandatalltimestoinsure
uninterruptedperformance.Theseminorpre-amptubeproblemscantakemanyformsbutcangenerallybedescribedintwo
categories:NoiseandMicrophonics.Noisecanbeintheformofcrackling,sputtering,whitenoise/hissand/orhum.Microphonic
problemsusuallyappearintheformofaringingorhighpitchedsquealingthatgetsworseasthegainorvolumeisincreased
thusaremorenoticeableinthehighergain“HI”modes.Microphonicproblemsareeasilyidentifiedbecausetheproblemisstill
presentevenwiththeinstruments’volumeofforunpluggedaltogether-unlikepick-upfeedbackwhichceasesastheinstru-
mentisturneddown.Microphonicnoiseiscausedbymechanicalvibrationandshock:thinkofbangingamicrophonearound
andyou’llunderstandwherethewordcamefrom.
Thebestwaytoapproachapre-amptubeproblemistoseeifitoccursonlyinonespecificmodeorchannel.Thisshouldlead
youtothetubeneedingreplacement.Thenallthatremainsistoswapthesuspecttubeforaknowngoodperformer.Ifyou
cannotnarrowdownthetroubletoaspecificmodeorchannel,theproblemmaybethesmalltubethatdrivesthepowertubes
whichisoperationalinallmodesandchannels.Thoughrare,aproblemwiththedrivertubewouldshowupinallaspectsof
performance-soifyoucan’tnarrowtheproblemdowntobeingmodeorchannelspecific,youmaywanttotryreplacingthe
drivertube.Driverproblemsgenerallyshowthemselvesintheformofcracklingorhuminallmodesofperformanceand/or
weakoveralloutputfromtheamplifier.Occasionallyananemicdrivertubewillcausetheamplifiertosoundflatandlifeless,but
thisissomewhatuncommon,aswornpowertubesareamorelikelysuspectforthistypeofproblem.
Sometimesmakingthediagnosisismoretroublethanit’sworthandit’sfasterandeasiertomerelyreplacethesmallpre-amp
tubesONEATATIMEwithareplacementknowntobegood.ButMAKESUREyoukeepreturningthetubestotheiroriginal
socketuntilyouhittheonethatcurestheproblem.You’llnoticethattubeslocatednearertotheINPUTjackalwayssound
noisier...butthisisbecausetheyareatthestartofthechainandtheirnoisegetsamplifiedoverandoverbythetubesthatfollow.
Thetubethatgoesintothis“inputsocket”(usuallylabeledV1)needstobetheleastnoisyofthebunch.Thetubethatgoesat
theendofthepreampchain-justaheadofthepowertubes-canbequitenoisywithoutcausinganyproblematall.Thetubes
inyouramphavealreadybeenlocatedinthemostappropriatesocketsandthisiswhyyoushouldNEVERpullthemalloutat
onceandALWAYSswapthemoneatatime.ALWAYSreturnaperfectlygoodtubetoitsoriginalsocket.Alsoit’sagoodidea
toputtheamponSTANDBYwhenswappingtubestoreducetheheatbuildupinthetubesthemselvesandtopreventexplosive
noises(whichcanstilloccurevenifyouarepullingthetubesawayfromtheirsocketsgently)fromcomingthroughthespeaker.
Remember,takeyourtime,bepatientandchancesarerealgoodthatyoucanfixyourampyourselfbyfindingandreplacingthe
badtube.Itkillsustoseesomeonewhohasshippedtheirampbacktous...andallitneededwasasimpletubereplacement!
Ifyoumustsendbackyouramp,removethechassisfromthecabinetbyunscrewingthefourmountingboltsonthebottom
top.Thechassisthenslidesbacklikeadrawerandcomesoutfromtheback.Removethebigpowertubesandmarkthem
accordingtotheirlocationfromlefttoright1,2etc.Theyneedtobewrappedseparatelywithplentyofwaddedupnewspaper
aroundthemandputinasmallerboxwithinthelargercarton.RemovetheRectifiertubesandwrapthemalso.Youcanleave
thepreamptubesinorremovethemandwrapthemseparatelybeingsuretolabeltheirlocation.(SeeTubeTaskChart.)
Towrapthechassis,useplentyoftightlywaddedupnewspapersothereisatleastsixinchesof“crushspace”betweenthe
chassisandthecardboardbox.Bubblewrapalsoworkswell,butpleaseDON’Tusestyrenepeanuts-theywillshiftduring
transitandgetlodgedinsideyourelectronicsaswellasallowingyouramptoendupatthebottomoftheboxunprotectedand
possiblydamaged.
Pre-amptubesdon’tnormallywearoutasarule.Therefore,itisnotagoodideatochangethemjustforthesakeofchanging
them.Ifthereisn’taproblem-don’tfixit.Ifthereisnoresultfromyoursubstitutions,itmaybepossiblethatyouhavemorethan
oneproblematictube.Thoughrare,thisdoeshappenandthoughitmakesthetroubleshootingprocessalittlemoreintimidating,
itisstillpossibletocuretheproblemyourself.
NOTE:Itisnormaltohearaslightmetallicringingsoundwhentappingonthepreamptubes.Aslongasthetubedoesnotbreak
intooscillationorstartcracklingoranyotherformofbizarrenoise,itisconsiderednormalandfunctional.

Mesa/Boogie Mini Rectifier Twenty-Five Specifications

General

Brand	Mesa/Boogie
Model	Mini Rectifier Twenty-Five
Category	Musical Instrument Amplifier
Language	English