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Mesa/Boogie Mini Rectifier Twenty-Five - Page 30

Mesa/Boogie Mini Rectifier Twenty-Five
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voltageī˜ƒandī˜ƒcurrentī˜ƒare:ī˜ƒWhenī˜ƒyouī˜ƒscrapeī˜ƒyourī˜ƒfeetī˜ƒacrossī˜ƒaī˜ƒcarpetedī˜ƒfloorī˜ƒinī˜ƒdry,ī˜ƒwinteryī˜ƒconditions,ī˜ƒyourī˜ƒbodyī˜ƒcanī˜ƒbecomeī˜ƒ
chargedī˜ƒwithī˜ƒ50,000ī˜ƒtoī˜ƒ100,000ī˜ƒvoltsī˜ƒofī˜ƒstaticī˜ƒelectricity.ī˜ƒī˜ƒAndī˜ƒwhenī˜ƒyouī˜ƒreachī˜ƒforī˜ƒtheī˜ƒdoorī˜ƒknob,ī˜ƒaī˜ƒsparkī˜ƒjumpsī˜ƒandī˜ƒyouī˜ƒfeelī˜ƒ
it!ī˜ƒī˜ƒTheī˜ƒvoltageī˜ƒisī˜ƒsuperī˜ƒhighī˜ƒbutī˜ƒtheī˜ƒcurrentī˜ƒ(measuredī˜ƒinī˜ƒmicro-amps)ī˜ƒisī˜ƒtinyī˜ƒ-ī˜ƒotherwiseī˜ƒyouī˜ƒwouldī˜ƒdieī˜ƒfromī˜ƒelectrocution.
Contrastī˜ƒthisī˜ƒwithī˜ƒyourī˜ƒcarī˜ƒbattery,ī˜ƒwhichī˜ƒputsī˜ƒoutī˜ƒaī˜ƒmereī˜ƒ12ī˜ƒvolts.ī˜ƒī˜ƒYouī˜ƒcanī˜ƒlayī˜ƒyourī˜ƒhandsī˜ƒrightī˜ƒacrossī˜ƒtheī˜ƒterminalsī˜ƒandī˜ƒnotī˜ƒ
feelī˜ƒaī˜ƒthing.ī˜ƒī˜ƒYetī˜ƒtheī˜ƒamountī˜ƒofī˜ƒcurrentī˜ƒavailableī˜ƒcanī˜ƒrunī˜ƒtoī˜ƒseveralī˜ƒhundredī˜ƒamperesī˜ƒ..ī˜ƒenoughī˜ƒtoī˜ƒturnī˜ƒoverī˜ƒaī˜ƒcoldī˜ƒengineī˜ƒandī˜ƒ
getī˜ƒitī˜ƒstarted.
Soī˜ƒcurrentī˜ƒandī˜ƒvoltageī˜ƒareī˜ƒtwoī˜ƒtotallyī˜ƒseparateī˜ƒelectricalī˜ƒparametersī˜ƒā€”ī˜ƒthoughī˜ƒwhenī˜ƒyouī˜ƒmultiplyī˜ƒthemī˜ƒtogether,ī˜ƒyouī˜ƒgetī˜ƒ
POWER,ī˜ƒwhichī˜ƒisī˜ƒmeasuredī˜ƒinī˜ƒwatts.
Whenī˜ƒyouī˜ƒsetī˜ƒtheī˜ƒbiasī˜ƒofī˜ƒanī˜ƒamplifier,ī˜ƒyouī˜ƒareī˜ƒadjustingī˜ƒtheī˜ƒstaticī˜ƒVOLTAGEī˜ƒatī˜ƒtheī˜ƒcontrolī˜ƒgridī˜ƒofī˜ƒtheī˜ƒtubeī˜ƒinī˜ƒorderī˜ƒtoī˜ƒproduceī˜ƒ
aī˜ƒdesiredī˜ƒamountī˜ƒofī˜ƒidleī˜ƒCURRENTī˜ƒflowingī˜ƒtoī˜ƒtheī˜ƒtubeā€™sī˜ƒplate.ī˜ƒī˜ƒAī˜ƒsmallī˜ƒchangeī˜ƒinī˜ƒgridī˜ƒvoltage,ī˜ƒproducesī˜ƒaī˜ƒlargeī˜ƒchangeī˜ƒinī˜ƒtheī˜ƒ
amountī˜ƒofī˜ƒcurrentī˜ƒflowingī˜ƒā€”ī˜ƒandī˜ƒthatā€™sī˜ƒbasicallyī˜ƒhowī˜ƒaī˜ƒtubeī˜ƒworks.ī˜ƒī˜ƒSayī˜ƒthatī˜ƒagainī˜ƒbecauseī˜ƒitā€™sī˜ƒsuperī˜ƒimportant:ī˜ƒī˜ƒAī˜ƒsmallī˜ƒ
changeī˜ƒinī˜ƒvoltageī˜ƒatī˜ƒtheī˜ƒgridī˜ƒcausesī˜ƒaī˜ƒlargeī˜ƒchangeī˜ƒinī˜ƒcurrentī˜ƒflowingī˜ƒtoī˜ƒtheī˜ƒplate.ī˜ƒī˜ƒSee,ī˜ƒthatā€™sī˜ƒtheī˜ƒessenceī˜ƒofī˜ƒamplification:ī˜ƒAī˜ƒ
smallī˜ƒchangeī˜ƒcausingī˜ƒaī˜ƒlargeī˜ƒchange.ī˜ƒī˜ƒAndī˜ƒhereī˜ƒitā€™sī˜ƒaī˜ƒsmallī˜ƒvoltageī˜ƒchangeī˜ƒcausingī˜ƒaī˜ƒlargeī˜ƒcurrentī˜ƒchange.
Theī˜ƒbiasī˜ƒconditionsī˜ƒareī˜ƒwhatī˜ƒdeterminesī˜ƒhowī˜ƒmuchī˜ƒcurrentī˜ƒflowsī˜ƒthroughī˜ƒtheī˜ƒbigī˜ƒpowerī˜ƒtubesī˜ƒwhenī˜ƒyouā€™reī˜ƒnotī˜ƒplaying.ī˜ƒī˜ƒAndī˜ƒ
whatī˜ƒdrivesī˜ƒyourī˜ƒspeakersī˜ƒisī˜ƒfluctuationsī˜ƒinī˜ƒthatī˜ƒcurrentī˜ƒflowī˜ƒwhenī˜ƒyouī˜ƒAREī˜ƒplaying.ī˜ƒī˜ƒIfī˜ƒtheī˜ƒamountī˜ƒofī˜ƒcurrentī˜ƒincreasesī˜ƒandī˜ƒ
decreasesī˜ƒ440ī˜ƒtimesī˜ƒperī˜ƒsecond,ī˜ƒthenī˜ƒyouā€™llī˜ƒhearī˜ƒanī˜ƒAī˜ƒnote.ī˜ƒī˜ƒIfī˜ƒtheī˜ƒfluctuationsī˜ƒinī˜ƒcurrentī˜ƒflowī˜ƒareī˜ƒlargeī˜ƒandī˜ƒstillī˜ƒatī˜ƒ440ī˜ƒperī˜ƒ
second,ī˜ƒyouā€™llī˜ƒhearī˜ƒanī˜ƒAī˜ƒthatī˜ƒisī˜ƒLOUD!
Butī˜ƒforī˜ƒpurposesī˜ƒofī˜ƒbiasing,ī˜ƒitā€™sī˜ƒtheī˜ƒamountī˜ƒofī˜ƒā€œplateī˜ƒcurrentā€ī˜ƒflowingī˜ƒwithī˜ƒnoī˜ƒsignalī˜ƒappliedī˜ƒthatā€™sī˜ƒimportant.ī˜ƒī˜ƒUnfortunatelyī˜ƒ
currentī˜ƒisī˜ƒhardī˜ƒtoī˜ƒmeasureī˜ƒbecauseī˜ƒtheī˜ƒcircuitī˜ƒmustī˜ƒbeī˜ƒinterruptedī˜ƒā€”ī˜ƒasī˜ƒinī˜ƒā€œcutī˜ƒtheī˜ƒwireā€ī˜ƒā€”ī˜ƒandī˜ƒtheī˜ƒmeterī˜ƒsplicedī˜ƒā€œinī˜ƒseriesā€ī˜ƒ
withī˜ƒtheī˜ƒbrokenī˜ƒcircuit.ī˜ƒī˜ƒButī˜ƒmeasuringī˜ƒVOLTAGEī˜ƒisī˜ƒeasy.ī˜ƒī˜ƒItī˜ƒisī˜ƒnotī˜ƒnecessaryī˜ƒtoī˜ƒinterruptī˜ƒtheī˜ƒcircuitī˜ƒbecauseī˜ƒaī˜ƒvoltageī˜ƒreadingī˜ƒ
canī˜ƒbeī˜ƒtakenī˜ƒinī˜ƒPARALLELī˜ƒwithī˜ƒtheī˜ƒcircuitī˜ƒintact.
Thus,ī˜ƒasī˜ƒaī˜ƒmatterī˜ƒofī˜ƒconvenience,ī˜ƒmostī˜ƒbiasī˜ƒsettingsī˜ƒareī˜ƒgivenī˜ƒinī˜ƒvoltsī˜ƒatī˜ƒtheī˜ƒgridī˜ƒ...ī˜ƒevenī˜ƒthoughī˜ƒcurrentī˜ƒthroughī˜ƒtheī˜ƒplateī˜ƒisī˜ƒ
theī˜ƒimportantī˜ƒfactor.ī˜ƒī˜ƒInī˜ƒfactī˜ƒplateī˜ƒcurrentī˜ƒisī˜ƒsoī˜ƒinconvenientī˜ƒ(andī˜ƒdangerous)ī˜ƒtoī˜ƒmeasureī˜ƒthatī˜ƒFenderī˜ƒdoesnā€™tī˜ƒevenī˜ƒstateī˜ƒwhatī˜ƒ
theī˜ƒcorrectī˜ƒvalueī˜ƒshouldī˜ƒbe.ī˜ƒī˜ƒTheyī˜ƒonlyī˜ƒgiveī˜ƒtheī˜ƒgridī˜ƒvoltageī˜ƒthatī˜ƒwillī˜ƒproduceī˜ƒthatī˜ƒcurrent.ī˜ƒī˜ƒ(Thatā€™sī˜ƒtheī˜ƒminusī˜ƒ52.)ī˜ƒī˜ƒButī˜ƒthatī˜ƒonlyī˜ƒ
happensī˜ƒifī˜ƒtheī˜ƒtubesī˜ƒbeingī˜ƒusedī˜ƒareī˜ƒā€œinī˜ƒspec.ā€
Asī˜ƒlongī˜ƒasī˜ƒtheī˜ƒtubesī˜ƒAREī˜ƒā€œinī˜ƒspecā€,ī˜ƒtheī˜ƒrightī˜ƒbiasī˜ƒvoltageī˜ƒwillī˜ƒalwaysī˜ƒgiveī˜ƒtheī˜ƒcorrectī˜ƒplateī˜ƒā€œCURRENTā€ī˜ƒā€”ī˜ƒbutī˜ƒthenī˜ƒthereā€™sī˜ƒnoī˜ƒ
needī˜ƒforī˜ƒtheī˜ƒbiasī˜ƒvoltageī˜ƒtoī˜ƒbeī˜ƒadjustable!
Ifī˜ƒtheī˜ƒtubesī˜ƒareī˜ƒNOTī˜ƒinī˜ƒspec,ī˜ƒthenī˜ƒtheī˜ƒonlyī˜ƒproperī˜ƒwayī˜ƒtoī˜ƒre-setī˜ƒtheī˜ƒbiasī˜ƒisī˜ƒtoī˜ƒcutī˜ƒtheī˜ƒcircuitī˜ƒandī˜ƒmeasureī˜ƒtheī˜ƒcurrentī˜ƒwhileī˜ƒ
adjustingī˜ƒtheī˜ƒbiasī˜ƒ...ī˜ƒbutī˜ƒnoī˜ƒmanufacturerī˜ƒIī˜ƒknowī˜ƒevenī˜ƒSTATESī˜ƒtheī˜ƒdesiredī˜ƒcurrentī˜ƒvalue!ī˜ƒī˜ƒBeī˜ƒthatī˜ƒasī˜ƒitī˜ƒmay,ī˜ƒwhenī˜ƒtheī˜ƒoriginalī˜ƒ
biasī˜ƒvoltageī˜ƒisī˜ƒalteredī˜ƒfarī˜ƒenough,ī˜ƒitī˜ƒwillī˜ƒcompensateī˜ƒforī˜ƒtheī˜ƒtubeā€™sī˜ƒabnormalī˜ƒperformanceī˜ƒandī˜ƒtheī˜ƒcorrectī˜ƒamountī˜ƒofī˜ƒidleī˜ƒcur-
rentī˜ƒflowī˜ƒmayī˜ƒthenī˜ƒbeī˜ƒrestored.ī˜ƒī˜ƒClearlyī˜ƒthisī˜ƒisī˜ƒsomethingī˜ƒmostī˜ƒrepairī˜ƒtechsī˜ƒshouldī˜ƒnotī˜ƒattempt.
Someī˜ƒnewerī˜ƒampsī˜ƒhaveī˜ƒLEDī˜ƒindicatorsī˜ƒconnectedī˜ƒtoī˜ƒtheī˜ƒcircuitī˜ƒwhichī˜ƒwillī˜ƒturnī˜ƒonī˜ƒwhenī˜ƒtheī˜ƒrightī˜ƒthresholdī˜ƒofī˜ƒcurrentī˜ƒflowī˜ƒ
hasī˜ƒbeenī˜ƒreached.ī˜ƒī˜ƒThisī˜ƒisī˜ƒanī˜ƒimprovement,ī˜ƒandī˜ƒalmostī˜ƒworthyī˜ƒifī˜ƒyouā€™reī˜ƒwillingī˜ƒtoī˜ƒacceptī˜ƒresistorsī˜ƒandī˜ƒlightsī˜ƒaddedī˜ƒintoī˜ƒyourī˜ƒ
amplifierā€™sī˜ƒaudioī˜ƒpathī˜ƒā€”ī˜ƒwhichī˜ƒweī˜ƒarenā€™t.ī˜ƒī˜ƒ
Theī˜ƒotherī˜ƒā€œadvantageā€ī˜ƒofī˜ƒthisī˜ƒsystemī˜ƒisī˜ƒthatī˜ƒitī˜ƒallowsī˜ƒsomeī˜ƒampī˜ƒmanufacturersī˜ƒtoī˜ƒavoidī˜ƒmatchingī˜ƒtheirī˜ƒpowerī˜ƒtubes.ī˜ƒī˜ƒTheī˜ƒ
thinkingī˜ƒisī˜ƒthatī˜ƒadjustingī˜ƒtheī˜ƒbiasī˜ƒtoī˜ƒeachī˜ƒtubeī˜ƒseparatelyī˜ƒeradicatesī˜ƒtheī˜ƒinherentī˜ƒdifferencesī˜ƒbetweenī˜ƒtheī˜ƒtubesī˜ƒbyī˜ƒinsuringī˜ƒthatī˜ƒ
theī˜ƒsameī˜ƒcurrentī˜ƒflowsī˜ƒthroughī˜ƒeachī˜ƒone.
Again,ī˜ƒthisī˜ƒhasī˜ƒsomeī˜ƒmeritī˜ƒ..ī˜ƒbutī˜ƒitā€™sī˜ƒstillī˜ƒnotī˜ƒasī˜ƒgoodī˜ƒasī˜ƒusingī˜ƒtubesī˜ƒthatī˜ƒareī˜ƒmatchedī˜ƒinī˜ƒtheī˜ƒfirstī˜ƒplaceī˜ƒbecauseī˜ƒcompensatingī˜ƒ
forī˜ƒtheī˜ƒmis-matchī˜ƒcausesī˜ƒtheī˜ƒpush-pullī˜ƒcircuitī˜ƒitselfī˜ƒtoī˜ƒbecomeī˜ƒunbalanced.ī˜ƒTwoī˜ƒwrongsī˜ƒdonā€™tī˜ƒreallyī˜ƒmakeī˜ƒaī˜ƒright.ī˜ƒ
BIAS ADJUSTMENT (Continued)
ī˜ƒī˜ƒī˜ƒī˜ƒ

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