Mercury Epiphone Valve Junior - Discharging Power Capacitors in Tube Amps; Safe Capacitor Discharge Techniques; Required Tools for Capacitor Discharge

Epiphone Valve Jr.•Mercury Upgrade Kit 45
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.
suchasPVCtubingoradowelrod.Makesure
enoughofthecopperwireisexposedtoactasa
contactpoint.
Step 5:Attachthealligatorcliptooneofthe
capacitor’sleads.Besuretheamplieris
completelypoweredoffbeforedoingso.
Step 6:TouchthebarewireendofthePVCtube
ordowelrodtotheotherleadofthecapacitor.It
isveryimportanttonottouchanyoftheexposed
leadsorwiresatthistime.Holdthebarewireonthe
leadforatleastseveralsecondstofullydischarge
thecapacitor.
Step 7:Testthecapacitorwithamultimetertobe
sureallvoltagehasbeensafelyremoved.
Discharging Capacitors
in a Guitar Tube Amp
Take pride in how safe you can be.
You can’t play guitar or build amps if you’re dead.
Youmayhaveheardvarioushorrorstoriesabout
thingsinsideampsthatcanstoreachargethatcan
killyou.Well,it’strue!However,thosedangerous
voltagescanbeeasilydrainedinjustafew
minutes,sotakeyourtimeanddon’trush.
Itisabsolutelyvitalthatwedraintheltercapacitors
intheDCpowersupplybeforeworkingonany
guitaramplier.Theseoftenholdachargeof
severalhundredvolts,whichispotentiallydeadly.
Capacitorscanholdtheirchargeforalongtime,
evenwiththepoweroffandtheampunplugged.It’s
veryimportantthatwelearntoproperly“drain”this
residualvoltagesothatwemaysafelyworkonthe
insideofourampliers.
What You’ll Need:
1. Safety glasses.Alwaysusesafetyglasses.If
youwireacapacitorinbackwardsthereisavery
goodchancethatitwillexplodeinyourface.
Ifyouhaven’tgiventhecapacitorsacoupleofdays
todischarge–orifyoujustwanttobecautious–
youcanuseashortlengthofinsulatedwirewith
alligatorclipsontheendstodischargethem.First,
makecertainthattheampisunplugged.Attach
onealligatorcliptoacapacitor’spositive(+)lead,
thentouchtheothercliptotheampchassisseveral
times.Repeattheprocedureforeachcapacitor
markedwithavoltage(VDC)ratinghigherthan25.
Thetimespentonthisprecautioncanspareyou
fromanumbingelectricshockthatyou’llremember
longaftertheampisbacktogether.
How to Discharge a Power
Capacitor in Tube Amp
by Kevin Krause
eHow contributing writer
Tobeabletoproperlytestandtroubleshootyour
tubeamplierwithamultimeteritisimportantto
dischargethecapacitorslocatedintheamp’spower
sectiontoavoidfalsereadings.Capacitorsactas
short-termbatteries,storingachargethatcanbe
calledonbyothercomponents.Thischargewill
remaininthecapacitorevenaftertheamphas
beenpoweredoff,andcanproducemisleading
voltagereadingsalongcircuitpaths.Becauseofthe
highlevelofthestoredpowerinthecapacitor,safe
dischargingisamust.
Thingsyou’llneed:
1. Highwattageresistor
2. Alligatorclip
3. Copperwire
4. PVCtubeordowelrod
5. Solderingiron
6. Solder
7. Multimeter
Instructions
Level of difculty: Moderate
Step 1:Stripabout1/4inchofinsulationoffeach
endofa2-footlengthofinsulatedcopperwire,and
solderoneendofthewiretooneoftheleadsof
ahighwattageresistor.Theresistancerequired
canbedeterminedbyadding5to50ohmsper
voltofthecapacitor’srating.Forinstance,a100V
capacitorwouldrequirearesistorratedanywhere
from500to5kohms.
Step 2:Attachtheotherendofthewiretoan
alligatorclip.
Step 3:Solderthefreeleadoftheresistortoa
shortpieceofbarecopperwire.
Step 4:Tapetheresistorandbarecopperwireto
oneendofalengthofnon-conductivematerial,
Filter Capacitor Discharge Tool