Epiphone Valve Jr.•Mercury Upgrade Kit 45
ThisprojectanditsdocumentationistheresultoftechnicalinvestigationsmadebytheengineeringstaffofMercury Magnetics.Thedisclosureoftheinformationhereinmaypertaintoproprietaryrightsand
thefurnishingofthesedocumentsdoesnotconstituteanexpresedorimpliedlicensetousesuchmaterials.
suchasPVCtubingoradowelrod.Makesure
enoughofthecopperwireisexposedtoactasa
contactpoint.
Step 5:Attachthealligatorcliptooneofthe
capacitor’sleads.Besuretheamplieris
completelypoweredoffbeforedoingso.
Step 6:TouchthebarewireendofthePVCtube
ordowelrodtotheotherleadofthecapacitor.It
isveryimportanttonottouchanyoftheexposed
leadsorwiresatthistime.Holdthebarewireonthe
leadforatleastseveralsecondstofullydischarge
thecapacitor.
Step 7:Testthecapacitorwithamultimetertobe
sureallvoltagehasbeensafelyremoved.
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.
Youmayhaveheardvarioushorrorstoriesabout
thingsinsideampsthatcanstoreachargethatcan
killyou.Well,it’strue!However,thosedangerous
voltagescanbeeasilydrainedinjustafew
minutes,sotakeyourtimeanddon’trush.
Itisabsolutelyvitalthatwedraintheltercapacitors
intheDCpowersupplybeforeworkingonany
guitaramplier.Theseoftenholdachargeof
severalhundredvolts,whichispotentiallydeadly.
Capacitorscanholdtheirchargeforalongtime,
evenwiththepoweroffandtheampunplugged.It’s
veryimportantthatwelearntoproperly“drain”this
residualvoltagesothatwemaysafelyworkonthe
insideofourampliers.
What You’ll Need:
1.
Safety glasses.Alwaysusesafetyglasses.If
youwireacapacitorinbackwardsthereisavery
goodchancethatitwillexplodeinyourface.
Ifyouhaven’tgiventhecapacitorsacoupleofdays
todischarge–orifyoujustwanttobecautious–
youcanuseashortlengthofinsulatedwirewith
alligatorclipsontheendstodischargethem.First,
makecertainthattheampisunplugged.Attach
onealligatorcliptoacapacitor’spositive(+)lead,
thentouchtheothercliptotheampchassisseveral
times.Repeattheprocedureforeachcapacitor
markedwithavoltage(VDC)ratinghigherthan25.
Thetimespentonthisprecautioncanspareyou
fromanumbingelectricshockthatyou’llremember
longaftertheampisbacktogether.
How to Discharge a Power
Capacitor in Tube Amp
by Kevin Krause
eHow contributing writer
Tobeabletoproperlytestandtroubleshootyour
tubeamplierwithamultimeteritisimportantto
dischargethecapacitorslocatedintheamp’spower
sectiontoavoidfalsereadings.Capacitorsactas
short-termbatteries,storingachargethatcanbe
calledonbyothercomponents.Thischargewill
remaininthecapacitorevenaftertheamphas
beenpoweredoff,andcanproducemisleading
voltagereadingsalongcircuitpaths.Becauseofthe
highlevelofthestoredpowerinthecapacitor,safe
dischargingisamust.
Thingsyou’llneed:
1. Highwattageresistor
2. Alligatorclip
3. Copperwire
4. PVCtubeordowelrod
5. Solderingiron
6. Solder
7. Multimeter
Instructions
Level of difculty: Moderate
Step 1:Stripabout1/4inchofinsulationoffeach
endofa2-footlengthofinsulatedcopperwire,and
solderoneendofthewiretooneoftheleadsof
ahighwattageresistor.Theresistancerequired
canbedeterminedbyadding5to50ohmsper
voltofthecapacitor’srating.Forinstance,a100V
capacitorwouldrequirearesistorratedanywhere
from500to5kohms.
Step 2:Attachtheotherendofthewiretoan
alligatorclip.
Step 3:Solderthefreeleadoftheresistortoa
shortpieceofbarecopperwire.
Step 4:Tapetheresistorandbarecopperwireto
oneendofalengthofnon-conductivematerial,
Filter Capacitor Discharge Tool