Mercury Epiphone Valve Junior - DANGER: Discharging Filter Capacitors; Filter Capacitor Safety Procedures; Safe Working Practices; Methods for Discharging Capacitors

44 Epiphone Valve Jr.•Mercury Upgrade Kit
ThisprojectanditsdocumentationistheresultoftechnicalinvestigationsmadebytheengineeringstaffofMercury Magnetics.Thedisclosureoftheinformationhereinmaypertaintoproprietaryrightsand
thefurnishingofthesedocumentsdoesnotconstituteanexpresedorimpliedlicensetousesuchmaterials.
DISCHARGING CAPACITORS–Thelter
capacitorsinanampwillretainachargeforquite
sometimeaftertheampisshutoffandunplugged.
Itisagoodideatomakesureyourampissafe
toworkon.Onewayistotakeawirewithan
INSULATEDalligatorcliponeachend,clipone
endtoagoodgroundpoint,andtheothertoone
oftheplateleadsfortherststagepreamptube.
Anothermethodwouldbetoputa100K,5Wor
moreresistorinlineofthesetwoclipsbyattaching
oneendtoground(rst),thentheothertothelter
capsthemselves.NEVERSHORTTHEMOUT
DIRECTLY!
BE THE ONE-ARMED TECHNICIAN –There
willcomeatimewhenyouhavetoworkona
chassisthatisrunning.Whendoingso,ifpossible
cliponeofyourmeter’stestleadstoground,and
useonlyonehandtoprobethecircuit,keeping
theotherinyourpocket,etc.ThatwayifyouDO
takeashock,yourheartisnotinlineofthepath
ofleastresistance–inonearmandouttheother.
WhenyouABSOLUTELYmustusetwohands,be
EXTREMELYCAREFUL,andusecommonsense,
butPLEASEtrytoavoidthesesituations!
***
“Filter”capscanstorefatalamountsofelectrical
current.Thecapsareconnectedneartherectier
andarepartofthepowersupply,andaidin
convertingACtoDC.Infact,theyareastandard
componentinanypowersupply.

Ifyou’recompletelylost,anddon’tunderstandthis,
DON’TMODIFYYOURAMP.Youhaven’tenough
knowledgetoworkonhighvoltage/currentcircuits
safely.

Severalwaystodischargecaps:
FIRST,UNPLUGTHEAMP!(Butthatdoesn’t
makeitsafe!)

THEN,takeascrewdriverorajumperandshort
thecapacitorsleads.
–ORjumperthepoweramptubeplatepinto
groundforaminuteorso(ClassA,singlepower
tubeonly)
–ORjumperthepositive(+)leadofeachlarge
captogroundforseveralseconds.Ajumperwith
abuilt-inresistor(10Korso)willhelpprevent
sparkshere.
Someorallofthesemethodsmayresultinaspark.
Obviously,youreshcanactasajumperalso.

It’sNEVERagoodideatotouchampcircuitrywhen
it’sswitchedon.Anddon’tworkonampsinbare
feet,oronadampbasementoor.
***
Lettingthecapacitorsdischargeslowlyispreferable
tohavingthemdoitallatoncethroughyourbody
whileyou’repokingaroundinsidetheamp.Having
thesuppliesyouneedonhandmakesthejobgo
faster.
You’llwantscrewdrivers,contactcleaner(youcan
useGunkbrandchokeandcarburetorcleaneror
WD-40),atoothbrushand–unlessyouownanair
compressor–anaerosolcanofcompressedair–
solderingsuppliesandavolt/ohmmeter(learnhow
tousethem!).
Startbyunpluggingtheampfromthewall,the
speakersfromtheamp,andremovingtheamp
chassisfromthecase.ForFenderamps,removing
thechassisinvolvesunscrewingtheupperback
casepanel,thenunscrewingthechassisfromthe
topofthecase.Putthescrews,nuts,andlock
washerswheretheywon’tgetlost.
Withthechassisoutofthecase,youcanlocate
theltercapacitorsyou’llwanttoavoidtouchingas
youperformthetune-up.Thesewillbecardboard
cylinders(usuallyorangeortanorvintageFenders)
with“+”printednearoneterminal.It’salsoagood
ideatosteerclearofwiringconnectedtothepower
transformerbecauseit’sadischargepathforthe
ltercapacitors.
DANGER! READ ME!
DISCHARGE THOSE FILTER CAPS!!!!!
The following is a collection of notes on discharging Filter Capacitors
CompiledbythestaffatMercury Magnetics