Mercury Epiphone Valve Junior User manual

VERSION 012011

2 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.
Ifyoudonotknowhowtoreadaschematic,westronglyrecommend
thatyoutakethisprojecttoaqualiedtechnicianforinstallation.
AllMercury Magneticsproductsare100%handmadebyusinCalifornia,USA.
Copyright©2006–2011byMercury Magnetics.AllRightsReserved.Mercury Magnetics,Multi-Choke,Mini-Choke
and“TheHeart&SoulofYourAmp”sloganaretrademarkslicencedtoMercury Magnetics.Axiom,APSandToneCloneare
registeredtrademarkslicensedtoMercury Magnetics.EpiphoneandValveJr.aretrademarksofGibsonGuitarCorp.Mercury
MagneticsisnotafliatedwithwithGibsonGuitarCorp.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.
Mercury MagneticsproductsareUL(UnderwritersLaboratoriesInc.)recognizedcomponentsfortheUSAandCanada.OBJY2
componentsystems,electricalinsulation,E120568.ULRecognition,class130(b)–Class200(n).OBJY8componentsystems,
electricalinsulation,certiedforCanada,class130(b)–Class200(n).
Mercury MagneticstransformersandotherproductsareincompliancewiththeEuropeanUnionRoHSDirective2020/95/ECwith
respecttothefollowingsubstances:lead(Pb),mercury(Hg),cadmium(Cd,hexavalentchromium(CR(VI)),polybrominatedbiphenyls
(PBB),andpolybrominateddiphenylethers(PBDE).
Attention: Modifying your Epiphone Valve Jr. amp voids the factory warranty!
Circuitry modications and design by
Sergio Hamernik and Alan Cyr
Manual written and designed by
Paul H. Smith
9167IndependenceAve.
Chatsworth,CA91311
(818)998-7791•FAX:(818)998-7835
Skype:paul.patroneteorpatrick.selfridge
www.MercuryMagnetics.com
[e-mail]
ThismanualisfortheValveJr.
PCB VERSION 2 or 3 ONLY!
(Pleaseseetheidenticationnotesinthis
manualtodeterminewhichversionyouhave.)

Epiphone Valve Jr. • Mercury Upgrade Kit 3
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.
SOLDERING NOTE: Depending upon the version your Valve Jr. may be assembled using RoHS compliant, lead-free solder. Working
with lead-free solder is different than standard solder. Generally a hotter iron is necessary. For more information we recommend doing
a web-earch for “lead-free soldering techniques.”
CAPACITOR DISCHARGE WARNING: Safe discharging of lter capacitors matters. It is essential for your safety and to prevent
damage to the amp’s circuitry, that large or high voltage capacitors be fully discharged before measurements are made, soldering is
attempted, or the circuitry is touched in any way. For information on how to do this, web-search “capacitor discharging.” Also see the
appendix for additional information.
CAPACITOR POLARITY: Note that many capacitors have positive and negative polarity, and are stamped accordingly. Be sure that
their polarity is correct when soldering to a PCB.
BRAIDING, TWISTING AND COILING LEADS: Do not braid, twist or coil the power transformer’s B+ lead wire. Check our reference
illustrations and photos to see which leads are twisted together. Typically only the lament leads of the power transformer. Other posi-
tioning of leads may be necessary to minimize amp noise. Follow are diagrams and instructs for optimal performance.
TRIMMING TRANSFORMER LEADS: To minimize noise, measure and trim the solderable lead lengths of the transformers and Mini-
Choke™. Route all wires cleaning around the tubes, chassis, etc.
CLIPPING vs. UNSOLDERING PCB COMPONENTS: To make this Upgrade it will be necessary to remove several components from
the Main PCB of the amp. Due to quality issues with modern off-shore PCB manufacturing, it can be difcult to unsolder an item without
creating other problems, the most typical of which is an eyelet detaching from the PCB. Therefore we’ve indicated which components
should be clipped vs. unsoldered. To unsolder heat your iron to 800ºF, then very quickly heating up one side of the existing solder con-
nection while pulling it through on the other. If the iron is not hot enough, or you linger too long, the eyelet will get damaged (or fall off).
If this happens you’ll have to fabricate a repair, or created a jumper to a trace. See this manual’s appendices for tips.
POWERING UP A GUITAR AMP: After making any modications to an amp’s circuit (e.g. this Upgrade) use a Variac along with an
current meter (some have both) to slowly apply power to the amp while checking for warning signs of circuitry errors or shorts. See the
section on “Using a Variac” at the end of this manual.
LOADING OUTPUT TRANSFORMERS: You must connect a speaker or speaker cab to your amp before powering it up. Without a
load the output transformer will blow.
MINI-CHOKE FACTOID: A Mercury Mini-Choke™ replaces a resistor and adds a disernable amount of tonal dimension to the circuit.
TRANSFORMER BREAK IN PERIOD: As a general rule, transformers require approximately 30 hours of playing time to be fully
broken in. Please refer to Mercury’s website for more information.
BE SAFE! ALWAYS USE PROTECTIVE EYEWEAR!
Table of Contents
Indentifying which Version of the amp you own . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
The Story Behind Mercury’s First Transformer Demonstration Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Parts List ..............................................................................7
Component Identication .................................................................8
Chassis Modication Diagram ............................................................10
Transformer and Mini-Choke specication sheets ............................................11
Wiring Schematics .....................................................................14
An Overview of the Upgrade Process ......................................................18
Mercury Upgrade Bonus -- Alan Cyr’s “6v6 Option” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Appendices:
Tips ’n Tricks – Using a Variac & Current Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Tips ’n Tricks – Making the Filmanent Supply Leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Tips ’n Tricks – Making the “RC Network” .................................................38
Tips ’n Tricks – Alan’s “Anti-Squeal” Circuit Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Tips ’n Tricks – Working on PCBs .......................................................40
Tips ’n Tricks – Reducing RF & Other Noise in the Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Tips ’n Tricks – Drilling the Tube Socket for the 6V6 Mod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
The Output Transformer Circuit .........................................................43
Discharging Filter Capacitors ...........................................................44
CAUTION! The voltages in your amplier can be dangerous. Transformers and chokes are not user servicable
parts. Installation of these components should always be performed by an experienced technician. The simple ability
to use a soldering iron is not enough to qualify a “do-it-yourself person.” Those who are inexperienced in working
with electronic circuits should never attempt to service their ampliers. Household line currents can be deadly!!
Transformers, chokes and large lter capacitors can store dangerous charges for several days, or longer, after the
amplier has been unplugged. Never touch the terminals of these components without being certain of their charge
status. Risk of shock and damage to equipment may result from mishandling and/or improper use of these compo-
nents. Please use common sense and always think safety rst. After all, great tone is most enjoyed when you are
alive to hear it.

4 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.
READ THIS FIRST! Identifying which verion of the amp you own.
Therearecurrentlyatleast3differentversionsoftheValve Junior’sPCB(printedcircuitboard)in
circulation.BeforeyoucanbegintheUpgradeyoumustidentifywhichversionyouhavesothatyoucan
usethecorrectUpgradeinstructionmanualandparts.Usethefollowingasaguide.
2 Basic Flavors and 3 Versions
TheValve Jr.comesin2avors:Headorcombo.
Bothampsarefundamentallythesame,usingthe
samecomponents.However,theoriginalVersion1
Valve Jrs.camewithasingle4ohmoutput,whereas
thelaterVersions2and3weregiven4,8and16
ohmoutputs.
Anothercluetodeterminingwhichversionyouhave
isthechassis.Examinethechassisphotosonthe
left.Noticethelocationofthetubesockets.
Also,Version1and2PCBsweregreen,
whereasversion3PCBsaredarkbrown
(almostblack).
OtherthanthecolorofthePCBs,
Versions2and3arenearlyidentical.
However,Epiphonedidchange
thevaluesofsomeoftheminor
componentsfromVersion2to
3(whichareindicatedinthe
illustrationsinthismanual).
Note:Thereare2tutorialson
theCD-ROM;onespecically
forVersion1andtheother(this
one)forVersions2and3PCBs.You’ll
needtousetheappropriatetutorialforthePCB
versionyouhave.
Valve Jr. Head
With4,8&16ohmoutputs
(Version2and3only).
Valve Jr. Combo
Version1,2andtheoriginal3sare4ohmoutput
only.NowallVersion3sare4,8and16ohm.
Stock Version 1
Chassis
Stock Version 2 & 3
Chassis
Note the relocation of
the tube sockets.

Epiphone Valve Jr.•Mercury Upgrade Kit 5
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.
The Story Behind Mercury’s
First Transformer Demonstration Project
W
aybackin’06yourfriendsatMercury
setouttocreateabasicdemonstration
toshowexactlywhatquality
transformerscoulddoforyourtone.Ourgoal
wastorevealthesoniccapabilitiesofhighquality
magnetics–i.e.properlydesignedvs.generic
transformers.
Whatstartedoutasasimpleeducationaldemo
endedupblowingthemindsofvirtuallyeveryone
whoheardit.Therewasnodenyinghow
extraordinaryourlittletestampsoundedafter
theMercurytrannyswere
installed....
The guinea pig
Fortheexperimentwechose
Epiphone’sremarkablevalue,
theall-tubeValve Jr:
• 5watts
• Single-ended,classAdesign
• Onegeneric12AX7preamp
tube
• OnegenericEL84powertube
• Genericpower&output
transformers
• Nochoke
Epiphone’s Valve Jr.isanidealdemonstration
platformforourpurposesbecauseitissucha
fundamental,stripped-downtubeamp.Withno
digitalcomponents,notoneknobs,noadded
f/xcircuits,nothin’...youjustcan’tgetanymore
elementaryandstillhaveaplayabletubeamp!
Allthisforaround$100.00–$150.00retail?Yes,but
asyoumightexpect,thestockampisratherdull
andanemic-sounding.
The Mercury Upgrades
TheMercury teamspentabout3months
workingonthelittleampbeforedecidinguponthe
bestsoundingcombinationofUpgradesand
adaptations.
TheprojectwasheadedbySergio Hamernik,
ofMercury Magnetics,andLosAngeles-
basedampwizard,Alan Cyr.Afterexaminingthe
originalcircuitryseveralcustomAxiom-series
transformersandMini-Chokesetsweredesigned
andtested.Alanwasthenabletocleanupthe
circuit,effectivelyopeningupthe
amp’ssoundbecausemuchof
theoriginalcircuitwasdesigned
togetaroundandreducenoise
generatedfromtheoriginal
trannys–nolongernecessary
bytheMercury Upgrades.
Theresultisaremarkably
tonefullittleampthatrunsquiet
andsoundsB-I-G.
Ifyouareanexperimenteryou
maywanttotrydifferentspeaker
and/ortubecongurations,
butoddlyenough,those
componentsdeliverrelativelyminortonalchanges
comparedtotheabsolutelyH-U-G-Eimprovement
oftheMercurytrannys.
HereinLosAngeles,theMercury Upgraded
Valve Jr.isoneofthehottest,mostin-demand
insiderampsaround.Thosewho’veheardit
immediatelywantone–andatsuchlowcostto
makethemods,whocanaffordNOTtoo!
Withthiskityou’llbeabletotransformyourbland
littleValve Jr. intoakeeper.
Continued on next page è

6 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.
Factoid:AMercuryMini-Choke™replacesaresistorand
addsadiscernableamountoftonaldimensiontothecircuit.
PerformyourownexperimentwhenworkingonyourValve Jr.—
tryitwithandwithoutthechokemodtothecircuit.You’llhave
nodifcultyhearinghowmuchbetteritsoundswiththechoke.
Chokeswereoriginallyusedinvintageampsbutseldomare
nowduetotheeconomicsofampbuilding(acostissue,nota
tonalone!).Chokesextendthelifeofthepower transformer
andrectier.Achokeismuchmorethanasimpleinductor.It
canalsostoreenergylikeacapacitor.Bettervoltageregulation
resultsfromusingachokethatputslessstressonyourpower
transformerhelpingittolivelonger.Chokespermithigher
loadcurrentstobedrawnfromvacuumtuberectierswithout
exceedingtheirpeakcurrentrating.Thismeanslifeextension
foryourtuberectier!Solidstaterectiersrunhappieraswell.If
that’snotenough,thetoneofyourampwillnoticeablyimprove
witha“peakedandtweaked”hand-tunedchokefromMercury.
You’ve made the Mercury Upgrade – now you’re ready to play!O
“State-of-the-Art”
Studio Samples
Followtheselinkstoaselectionofundoctored
MP3samplesoftheprototypeMercuryUpgraded
ValveJr.Justforthefunofitthesesampleswere
madeunderprimitiveconditions(seethephototo
theright).
Aspecial“Thankyou!”goesouttoLAmusician
PhilWoodwardforhisguitarworkonthese
tracks:
Mercury UpgradeSample1
Mercury UpgradeSample2
Mercury UpgradeSample3
Mercury UpgradeSample4
Mercury UpgradeSample5

Epiphone Valve Jr.•Mercury Upgrade Kit 7
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.
Parts List
YourMercuryUpgrade KitfortheEpiphone Valve Jr.(Version2or3PCBs)includesthesecomponents.
Transformers:
• MercuryAxiomPowerTransformer(part#:EPJR-P)............................................................................................... 1
• MercuryAxiomOutputTransformer(part#:EPJR-OM)4,8&16Woutputs............................................................ 1
• MercuryAxiomMini-Choke(part#:EPJR-C-3H)...................................................................................................... 1
Capacitors:
• 10mF25Vor50Velectrolytic(radial)................................................................................................................................ 1
• 22mF40Velectrolytic(axial)............................................................................................................................................. 1
• 22mF450Velectrolytic(axial).......................................................................................................................................... 2
• 22mF450Velectrolytic(radial).......................................................................................................................................... 2
• 270rFsilvermica.............................................................................................................................................................. 1
• 680rFsilvermica.............................................................................................................................................................. 1
Resistors:
• 100KW½Wcarbonlm..................................................................................................................................................... 2
• 220KW½Wcarbonlm..................................................................................................................................................... 1
• 470KW½Wcarbonlm..................................................................................................................................................... 1
• 1.5KW½Wcarbonlm...................................................................................................................................................... 2
• 1MW½Wcarbonlm........................................................................................................................................................ 1
• 470W2Wameproof........................................................................................................................................................ 1
• 3.3KW2Wameproof...................................................................................................................................................... 1
Misc. Components:
• CD-ROMwithphotographicinstructions(withschematics)............................................................................................. 1
• Jackinsulatorstoisolateinputjack.................................................................................................................................. 2
• Stand-offconnector,nut,washer&bolt...................................................................................................................... 1set
• 8-pintubesocket............................................................................................................................................................... 1
• 8-32—1/4”bolts,washers,lockingwashers&nuts(formountingthechoketothechassis)...................................2sets
• 8-32—1/2”bolts,washers,lockingwashers&nuts(formountingPTandOT)........................................................6sets
• 6”coilofUNSHIELDIEDbusswire.............................................................................................................................1coil
• 6”coilofwireinsulation“spaghetti”............................................................................................................................1coil
• 12”coilsofinsulatedblack,white,yellow,redandbluewire...................................................................................5coils
• Mercurymetalbadge.................................................................................................................................................... 1
• Mercuryguitarcasesticker........................................................................................................................................... 1
Alan’s 6V6 option components:InadditiontothestandardMercury Upgrade,youmayalsowanttoinstallAlan’s
6V6 option.It’sfairlysimpletodo,butrequiresaddingasockettothecircuit(anotherholeinthechassis).Thereisa
specialsectionofthismanualdedicatedtomakingAlan’s 6V6 option.Hereisthelistofcomponentsincludedwith
thiskit(6V6tubeNOTincluded)–
• 220KW½Wresistor(carbonlm)..................................................................................................................................... 1
Anti-squeal option:Ownersofsome,butnotall,Version3PCBampshavereportedanunusual“squeal”emittingfrom
theiramps.ThisrandomnoiseseemstoberelatedtothequalityoftheChinesecomponents.Werecommendthat
youDONOTinstallthisoptionunlessyouexperiencethisphenomenon.Thereisaspecialsectionofthemanual
dedicatedtoinstallingthisoption.Hereisthelistofcomponents(includedwiththekit)–
• 220KW½Wresistor(carbonlm)..................................................................................................................................... 1
• 47rFcapacitor(ceramicdisk)........................................................................................................................................... 1
Extra components note:Eachkitincludescomponentsforall3versionsoftheValve Junior’sPCB.However,only
thecomponentsyouneedforaVersion2and3PCBsUpgradearelistedabove(andonthenextpage).
IMPORTANT NOTE REGARDING VERSION 3 AMP ON/OFF SWITCHES:Donotattempttodisconnecttheleads
fromtheON/OFFswitchofyouramp.Wehavereceivednumerouskit-builderreportsthatanyoftheON/OFFswitches
literallyfallapartwithanyattempttodisconnecttheirleads!Instead,cutthewiressothatyoucanusewireconnectors.
We’reworkingonabettersolution.Butfornow,justcuttheleadssothattheycanbereconnectedwithwireconnectors.

8 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.
CAPACITORS (electrolytic)
CAPACITORS (silver mica) CAPACITORS
(ceramic disk)
1.5KΩ 1/2W
(brown/green/red)
470KΩ 1/2W
(yellow/violet/yellow)
~6 in.
UNSHIELDED
buss wire
~6 in.
wire insulation
“spaghetti”
Shielded ORANGE, RED, BLUE, BLACK & YELLOW wire
8-32, 1/4” bolt, nut, washer & lock
washer for attaching the Mini-Choke
to the chassis.
4-40, 1/4” bolt, nut & lock washer for attaching
the 8-pin tube socket to the chassis.
8-32, 1/2” bolt, nut, washer & lock
washer for attaching the output
& power transformers to the chassis.
EPJR-P
(power transformer)
EPJR-O 4Ω & EPJR-OM 4, 8 & 16Ω
(output transformer)
EPJR-C-3H
(Mini-Choke™)
1x
2x
1x
1x
1x
2x
2x
2x
6x
~12 in.
coils
1x
1x
1x
1x
1x
1x
2.2KΩ 1/2W
(red/red/red)
RESISTORS (carbon film) NUTS ’N BOLTS
OTHER COMPONENTS
RESISTORS (flame-proof)
Component Identification
Use these photos to identify the components needed to make your Version 2 or 3 PCB Upgrade:
10µF 25V or 50V
(radial)
680ρF 500V
680
1x
270ρF 500V
270
100KΩ 1/2W
(brown/black/yellow)
3.3KΩ 2W
(orange/orange/red)
1x
22µF 450V (radial)
22µF 450V
10µF 50V
Mercury nameplate
Note that most capacitors have +/- polarity. Be sure to study the
schematics for the correct directions when Upgrading your amp.
1MΩ 1/2W
(brown/black/green(
22µF 40V
axial
22µF
40V
470Ω 2W
(yellow/violet/brown(
220KΩ 1/2W
(red/red/yellow)
47ρF
47
ρF
8-pin
tube socket Stand-off connector
with nut, washer & bolt
1X 1X 1X 1X 2X

Epiphone Valve Jr.•Mercury Upgrade Kit 9
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.
Recommended tools for this project:
• SetofPhillipsscrewdrivers
• Wirestrippers
• Goodqualitysolderiron(capableoftempsat>800ºF)
• Electronicsgradesolder
• Soldersuckerand/orwick
• Dremel Toolwithpolishingandcarbidecuttingtips*
• ExactoknifeforcuttingandscrapingPCBtraces*
• Smallneedle-noseplyers
• Smallratchetset(AmericanandMetric)
Synopsis of Upgrade Sequence:
1. Disconnectchassisfromampanddischargethecaps.
2. Removeoldtransformers.
3. DisconnectMainandOutputPCBsandremove/
desoldercomponentsthatwillbechanged.
4. Drillnewtransformersandchokemountingholes.If
you’llbeaddingAlan’s6V6option,drillthesocketand
mountingscrewholesforthat.
5. Mounttransformersandchoke.Install6V6socketand
stand-offconnectorbracketifyouareaddingAlan’s
6V6option.
6. Drillholesforlamentwiresandenlargeholesfor
otherconnectionsintothemainPCB.
7. CuttracesonthemainPCB.
8. SolderbusswirejumperstothemainPCB.
9. Solderinupgrade’sresistorsandcapacitorsontothe
mainPCB.
10.MakeandsolderinlamentsupplyleadsbetweenV1
andV2(EL84and12AX7)sockets.
• Sharpknifeforscrapinginsulationlayerfromtraces
• Electricdrillwith1/16”and11/64”bits
• 1”and9/16”Varibitorsteppeddrillbit
• Silicongoo
• Loctite 290(green)
• PureisopropylalcoholandQ-tips
• Variacandcurrentmeter
*Dremel ToolcanbeusedtocuttracesanddrillholesinPCB.
11.Forthe6V6option,install8-pinsocket’scomponents
andconnectingleads.
12.SolderOT’sleadstotheoutput’sminiPCBand
reconnecttothechassis.
13.Completeconnectionstothe6V6option.
14.SolderremainingleadsforthePT,chokeandtheOT
tothemainPCBandtheOn/Offswitch.
15.ReattachmainPCBtochassis.
16.Usingthesupplieddiagrams,triple-checkyourwork
toensurethatallconnectionsaremadeandare
correct.
17.Powerupusingavariacandampmeter.
CAUTION: DO NOT POWER UP THE AMP
WITHOUT THE SPEAKER CONNECTED!!!!
18.ArrangeleadstominimizeRFandnoise.
Reference photo of a stock Version 2 or 3 Valve Jr. chassis. Photo shows external chassis layout of
transformers and tubes. Note that hte EL84 and 12AX7 tube (or valve) sockets are identical. Be care-
ful NOT to accidentally switch these tubes!
Original Power Transformer
Generic EL84
Power Tube
Tube Retainers
Original Output
Transformer
Generic 12AX7
Preamp Tube

10 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.
Epiphone Valve Jr. • Version 2 & 3 Chassis
Locations of Mercury Magnetics transformers & choke mounting hole modifications
Mercury Magnetics: 07-19-10
www.MercuryMagnetics.com
[email protected]
[phone] Back of chassis
3/16” dia. hole
3/16” dia. hole
3/16” dia. hole
Mercury’s
Axiom EPJR-P
POWER
TRANSFORMER
mounting
hole
locations
3-1/2”
Hole location:
2-1/16“ x 2” from the front
left-hand corner of the chassis
Hole location:
4“ x 2-3/16” from the front
left-hand corner of the chassis
Enlarge existing hole
Mercury’s
Axiom EPJR-C-3H
CHOKE
mounting
hole
locations
2”
Hole location:
9-1/8” x 4-1/4” from the front
left-hand corner of the chassis
6V6 Mod (only!)
Hole location:
6-1/2” x 5-1/4” from the front
left-hand corner of the chassis
1” dia. From the center of the 1“ dia. hole
drill 2 mounting screw holes
exactly 1-1/2” apart. Mercury’s
Axiom EPJR-O
OUTPUT TRANSFORMER
mounting hole locations
2.5” x 2” sq.
3/16” dia. holes
Front of chassis
(Outside chassis: 12-1/4” x 7”)
Copyright © 2006–2010 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks licensed to Mercury Magnetics. Axiom is a registered trademark licensed to Mercury Magnetics.
Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
3/16” dia. hole
1/8” dia. hole 1/8” dia. hole

Epiphone Valve Jr.•Mercury Upgrade Kit 11
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.
1-5/16”
2-1/2”
4“
3“
2-1/4“
1-5/16”
ORANGE/WHITE
YELLOW
ORANGE
RED RED
ORANGE
BLACK
YELLOW
RED
3-1/2“
3/16” DIA
RED
B+
YELLOW
BLACK
RED
SECONDARY
(OUTPUT)
ORANGE
ORANGE
6.3V with CT
filament
winding
ORANGE/WHITE
PRIMARY
(INPUT)
120V
Low flux/high impedance inductance design
with primary to secondary humbucking
winding configuration.
Mercury Magnetics
9167 Independence Ave. • Chatsworth, CA 91311
[phone] • FAX [phone]
[e-mail] • www.MercuryMagnetics.com
100% of our products are designed & handmade in So. California, USA. • Established in 1954
TM
(All dimensions are nominal)
EPJR-P
EPJR-P
CLASS: Axiom®
TYPE: Power Transformer
PART NO.: EPJR-P
ORIGINAL EPIPHONE PART NO: TC00273
MOUNTING: Horizontal A-Frame
VA RATING: 30VA
DATE: 03-30-06
Copyright © 2006–2010 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks licensed to Mercury Magnetics. Axiom is a registered trademark
licensed to Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
Epiphone Valve Jr.
Origin: Stock Valve Jr.
purchased in April 2005
specifically for modification
purposes.

12 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.
BLACK BLACK
BLACK
1-3/8“
1-11/16“
1-1/8“
9/16”
9/16”
3/16” DIA
2-3/8“
2“
BLACK
BLACK
3.0 Henry
200ma maxium
Mercury Magnetics
9167 Independence Ave. • Chatsworth, CA 91311
[phone] • FAX [phone]
[e-mail] • www.MercuryMagnetics.com
100% of our products are designed & handmade in So. California, USA. • Established in 1954
TM
Copyright © 2006–2010 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks licensed to Mercury Magnetics. Axiom is a registered trademark
licensed to Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
Epiphone Valve Jr.
Origin: Stock Valve Jr. purchased in April 2005 specifically
for modification purposes.
(All dimensions are nominal)
EPJR-C-3H
EPJR-C-3H
CLASS: Axiom®
TYPE: Mini-Choke™
PART NO.: EPJR-C-3H
ORIGINAL EPIPHONE PART NO.: N/A
NOTE: The introduction of the first Mini-Choke™. This choke was
specially designed by Mercury Magnetics for the Valve Jr. but may
also be used in almost any amp style. (Call for more information.)
MOUNTING: Horizontal A-Frame
POWER RANGE: 3 Henry / 200ma max.
DATE: 03-27-06

Epiphone Valve Jr.•Mercury Upgrade Kit 13
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.
2-1/2”
2”
2“
1”
GRAY
YELLOW
BLACK
YELLOW
GRAY
BLACK
GREEN
YELLOW
2“
3”
2-1/2”
BLACK
YELLOW
BLACK
Attach to Output Jack
Module “GND” (ground)
Attach
to PCB
location “T4”
Attach to PCB
location “T3”
(left hole)
GREEN (4Ω)
YELLOW (8Ω)
GRAY (16Ω)
Attach to Output Jack
Module “4R”
Attach to Output Jack
Module “8R”
Attach to Output Jack
Module “16R”
SECONDARY
(OUTPUT)
PRIMARY
(INPUT)
Mercury Magnetics
9167 Independence Ave. • Chatsworth, CA 91311
[phone] • FAX [phone]
[e-mail] • www.MercuryMagnetics.com
100% of our products are designed & handmade in So. California, USA. • Established in 1954
TM
(All dimensions are nominal)
EPJR-OM
MULTI-TAP VERSION
EPJR-OM
CLASS: Axiom®
TYPE: Output Transformer
PART NO.: EPJR-OM
ORIGINAL EPIPHONE PART NO.:
YW TF-VALVE JUNIOR-5W
MOUNTING: Horizontal L-Bracket
POWER RANGE: Our OTs are rated
to handle up to 50% more power than
the original manufacturer spec.
DATE: 04-24-07
MULTI-TAP VERSION
Copyright © 2006–2010 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks licensed to Mercury Magnetics. Axiom is a registered trademark
licensed to Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
Epiphone Valve Jr.
Origin: Stock Valve Jr.
purchased in April 2005
specifically for modification
purposes.

14 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.
B2 B1
B3 B3
.022 µ F
100KΩ
2.2KΩ
1.5KΩ
2.2KΩ
1.5KΩ
1.5KΩ
220KΩ
22
µ F 22
µ F 22 µ F
68KΩ
1MΩ
68KΩ
1MΩ
1MΩ
1MΩ
100KΩ
(Unmodified stock version • ”Version 2 & 3” PCBs)
220Ω 2W
.022
µ F
NOTE: Values in BLACK indicate
Version 2 PCBs, values in RED
indicate Version 3 PCBs.
R2
R1
R8
R3
V1B
C1 R6
R7
R4
R15
R14
R5
C2
V2
C3 C5
R9
VR1
V1A
C4
EL84
12AX7
12AX7
EL84
12AX7
Valve Junior Head
DRAWN BY MERCURY MAGNETICS
08-03-07
REV. 04-09-10
www.MercuryMagnetics.com
www.Amp-Exchange.com
This project and its documentation are 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 expressed or implied license to use
such materials. Copyright © 2006–8 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks of Mercury Magnetics. Axiom is a registered trademark of Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries.
Mercury Magnetics is not affiliated with Gibson Guitar Corp.
4Ω
8Ω
16Ω
B1 B2 B3
22 µ F
(to filaments DC)
220Ω
220KΩ
4.7KΩ 1W 10KΩ
22µF 22 µ F
R12 R13
C9
22 µ F
C6
4700 µ F
470
µ F
C12 C7
B3
.1 µ F
C11 C8
R10
R11
B1
D1-4

Epiphone Valve Jr.•Mercury Upgrade Kit 15
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.
B2
PRI SEC
B1
B3
B1 B2 B3
680ρF
47ρF
SQUEAL BYPASS
OPTION
B3
.022µF
100KΩ
1.5KΩ 2.2KΩ
4Ω
8Ω
16Ω
1.5KΩ
1.5KΩ
250-750ρF
220KΩ
220Ω 2W
470Ω
22µF
(AC to filaments)
B+ 3.3KΩ 1-2W 10KΩ
22µF
10µF 22µF
1MΩ
68KΩ
470KΩ
220KΩ
RC NETWORK
6V6 MOD OPTION
100KΩ
1MΩ
1MΩ
100KΩ
.022µF
22µF 22µF 22µF 22µF
Mercury
Magnetics
Axiom®
EPJR-P
power
transformer
Mercury Magnetics
Axiom® EPJR-C-3H
Mini-Choke™
R12 R13
C9 C6 C12 C7
B3
.1µF
C11 C8
R10
= Modification
= PCB location
= Squeal bypass
22-47µF
25V
Mercury
Magnetics
Axiom®
EPJR-OM (head)
output transformer
R2
R1 R8
R3
V1B
C1 R6
C11
R16
R7
R4
R15
D1-4
R14
R5
C2
V2 7
9
3
2
8
4
3
5
C3 C5
R9
VR1
V1A
C4
12AX7
12AX7
12AX7 EL84/7189
6V6
12AX7
VERSION: 05-09-06 (original)
6V6 REV. 07-28-08 (updated)
REV. 12-02-10
Valve Jr. head • Mercury Upgrade with 6V6 Mod
This project and its documentation are 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 expressed or implied license to use such materials. Copyright © 2006–9 by Mercury Magnetics. All Rights Reserved. Axiom and ToneClone are registered trademarks of Mercury Magnetics. Mercury Magnetics, “The Heart & Soul of Your Amp,” FatStack & Mercury
Vintage are trademarks of Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries.
Mercury Magnetics is not affiliated with Gibson Guitar Corp.
FILAMENT CONNECTION
TYPE EL84 6V6*
*You can use 6V6, 6L6, 6550, etc.
PINS 4 & 5  2 & 7
(Alan Cyr / Mercury Magnetics • Version 2 & 3 PCBs)
9167 Independence Ave., Chatsworth CA 91311 • [phone]
www.MercuryMagnetics.com • www.Amp-Exchange.com
12AX7
1
2
3
4 5 6
7
8
9
HT 2P
2G
2K
H
H
IP
IG
IK
6V6
3
2
1 8
7
4 5
H
Nc K
H
P
G2 G1
EL84
1
2
3
4 5 6
7
8
9
Ic
G1
K
H
H
Ic
P
Ic
G2

16 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.
B2 B1
B3
B1 B2 B3
B3
.022 µ F
100KΩ
2.2KΩ
1.5KΩ
2.2KΩ
1.5KΩ
1.5KΩ
220KΩ
22
µ F
22 µ F
(to filaments DC)
220Ω
220KΩ
4.7KΩ 1W 10KΩ
22
µ F 22
µ F
68KΩ
1MΩ
68KΩ 1MΩ
1MΩ 1MΩ
100KΩ .022
µ F
22 µ F 22 µ F
(Unmodified stock version • ”Version 2 & 3” PCBs)
R12 R13
C9
22 µ F
C6
4700 µ F
470
µ F
C12 C7
B3
.1 µ F
C11 C8
R10
R11
B1
220Ω 2W
R2
R1
R8
R3
V1B
C1 R6
R7
R4
R15
D1-4
R14
R5
C2
V2
C3 C5
R9
VR1
V1A
C4
12AX7 EL84
12AX7
12AX7 EL84
12AX7
Valve Junior Combo
DRAWN BY MERCURY MAGNETICS
05-09-06
REV. 04-09-10
www.MercuryMagnetics.com
www.Amp-Exchange.com
This project and its documentation are 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 expressed or implied license to use
such materials. Copyright © 2006–8 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, ToneClone, FatStack & Mercury Vintage are trademarks of Mercury Magnetics. Axiom is a registered trademark of Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries.
Mercury Magnetics is not affiliated with Gibson Guitar Corp.
NOTE: Version 3 EVJ Combos are now appearing
with 4, 8 & 16Ω outputs. See the head version
of the schematic if you have one of these amps.
NOTE: Values in BLACK indicate
Version 2 PCBs, values in RED
indicate Version 3 PCBs.

Epiphone Valve Jr.•Mercury Upgrade Kit 17
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.
B2
PRI SEC
B1B3
B1 B2 B3
680ρF
47ρF
SQUEAL BYPASS
OPTON
B3
.022µF
100KΩ
1.5KΩ2.2KΩ
1.5KΩ
1.5KΩ
250-750ρF
220KΩ
220Ω 2W
470Ω
22µF
(AC to filaments)
B+ 3.3KΩ 1-2W 10KΩ
22µF
10µF22µF
1MΩ
68KΩ
470KΩ
220KΩ
RC NETWORK
6V6 MOD OPTION
100KΩ
1MΩ
1MΩ
100KΩ
.022µF
22µF22µF22µF22µF
Mercury
Magnetics
Axiom®
EPJR-P
power
transformer
Mercury
Magnetics
Axiom®
EPJR-C-3H
mini-choke
R12 R13
C9C6 C12 C7
B3
.1µF
C11C8
R10
22-47µF
25V
Mercury
Magnetics
Axiom®
EPJR-O (combo) or
output transformer
= Modification
= PCB location
= Squeal bypass
R2
R1
R8
R3
V1B
C1 R6
R7
R4
R15
D1-4
R14
R5
C2
V2 7
9
3
2
8
4
3
5
C3 C5
R9
VR1
V1A
C4
12AX7
12AX7
EL84/7189
6V6
12AX7
FILAMENT CONNECTION
TYPE EL84 6V6*
*You can use 6V6, 6L6, 6550, etc.
PINS 4 & 5  2 & 7
VERSION: 05-09-06 (original)
6V6 REV. 07-28-08 (updated)
REV. 04-09-10
Valve Jr. head • Mercury Upgrade with 6V6 Mod
This project and its documentation are 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 expressed or implied license to use such materials. Copyright © 2006–9 by Mercury Magnetics. All Rights Reserved. Axiom and ToneClone are registered trademarks of Mercury Magnetics. Mercury Magnetics, “The Heart & Soul of Your Amp,” FatStack & Mercury
Vintage are trademarks of Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries.
Mercury Magnetics is not affiliated with Gibson Guitar Corp.
(Alan Cyr / Mercury Magnetics • Version 2 & 3 PCBs)
9167 Independence Ave., Chatsworth CA 91311 • [phone]
www.MercuryMagnetics.com • www.Amp-Exchange.com
12AX7
1
2
3
456
7
8
9
HT2P
2G
2K
H
H
IP
IG
IK
6V6
3
2
18
7
45
H
Nc K
H
P
G2 G1
EL84
1
2
3
456
7
8
9
Ic
G1
K
H
H
Ic
P
Ic
G2

18 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.
ReadthethismanualBEFOREbeginningthe Upgrade.Inthatwayyou’llbemoreawareof
what’srequiredandwhetherornotitiswithinyour
ability.Also,besuretoreadthroughthevarious
appendicesforhelpfulhintsandtips.Ifyouhave
anyquestions,pleasedonothesitatetocallushere
atMercury Magnetics!
OUTLINE
You’reabouttostripyourstockampandprepareitfor
theMercury Upgrade.It’sgoodpracticetoplaceall
ofthecomponentsyouremoveintoholdingcontainers
sotheyareeasytolocateandwon’tgetlost.Mostofthe
componentsyouarestrippingwillnotbeusedagain.But
holdontoeverythingfornowuntilyourUpgradedamp
isupandrunning.
Let’sgetstarted:
1. Unplugtheampfromthepowersource(AC).
2. Removeallchassisretainingscrewsfromtheback
andthetwoonthetopoftheamp.
3. Removethechassisfromtheamp–disconnectthe
twospeakerwiresrst.
4. Dischargethecapacitors.
5. RemovethefollowingfromtheMainPCB(printed
circuitboard):
a. Tubes
b. Transformerclips
c. UnboltthemainPCB.
d. Unclipand/orunsolderallotherdirectconnections
tothemainPCB.
e. Unboltandremovethestockoutputandpower
transformers
Special note:Thesolderusedintheseampsis
RoHScompliant–atermforanewindustrystandard
thatbasicallymeansthesolderislead-free.This
alsomeansthatyou’llneedtouseagoodquality
ironrunninghotterthantraditionalsoldermelting
temperatures(setitforabout800°F)–RoHS
compliantsoldermeltsathighertempsthanthe
originalsolderingalloysbutit’slikelyyou’llbeusing
regularelectronicssolderforthisproject.Youmayalso
wanttodoawebsearchtostudyuponworkingwith
RoHSsolder.
Fordrillingorresizingholeswerecommendthatyouuse
aDremel Toolwitha1/16"bit.Aholereamingbitwillalso
comeinhandytoenlargeexistingholes.Andasmall
grindingheadwillserveasatrace-cutter.Asharppocket
knifeorExactoisrecommendedforscrapingawayPCB
insulationtorevealtraces.
Seeappendixesforspecialinstructionsregardingtrace
cutting,tracerevealing,andaddingjumpers.
6. Usetheillustrationsasareferencetostripthemain
PCBinthisorder:
a. Unsolderitems
b. Holedrillingandenlarging
c. Cuttraces
d. Revealtraces
e. Addjumpers
7. Carefullycompareyourstrippedandmodied
MainPCBsothatitmatchestheillustrationsinthis
Sequence.Amissedstepormistakewillbiteyoulater
on.Takeyourtimetodoamethodicalandthorough
approach.
8. Thechassisneedstobemodiedtoholdthe
Upgradedpower andoutput transformerandthe
Mini-Choke.Ifyouwillbeaddingthe6V6 Mod,you’ll
needtoaddthetubesocketaswell.Referencethe
chassistemplate,makethemodicationsandbolton
thetransformersandMini-Choke.Ifyou’llbeaddingthe
6V6Mod,seethespecialsectionregardinghow.
VERSION 2 & 3 PCBs ONLY!
An Overview of the Upgrading Process

Epiphone Valve Jr.•Mercury Upgrade Kit 19
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.
T7 T8 T9
T3
V2
V1
T10 T11
T12
GND
C6
C9
C7
C8
T1
T2 D3
T4
T5 R10
R11
T6
B1
C12 D4
D1 D2
IN
G
IN S10 G
VALVE JUNIOR
VER051122
HBO1570
9
8
7
6
5
4
3
2
1
1
9
8
7
6
5
4
3
2
1
1
R12
R14
C3
C5
JP3
C4
R2
R15
R5
R4
R3
C1
R13
R1
R8
JP1
JP2
R9 R6 R7
C2
C11
68KΩ
(V2) 68KΩ
(V3) 1MΩ
100KΩ
100KΩ
10KΩ 4.7KΩ
220Ω 220KΩ
220KΩ
220Ω
1.5KΩ
(V2) 2.2KΩ
(V3) 1.5KΩ (V2) 2.2KΩ
(V3) 1.5KΩ 1MΩ
1MΩ
22µF
22µF
(V2) 4700µF
(V3) 470µF
22µF 22µF 22µF
22µF
22µF
.022µF
.022µF
.1µF
VERSION: 05-09-06 (original)
6V6 REV. 07-28-08 (updated)
www.MercuryMagnetics.com
www.Amp-Exchange.com
Valve Jr. • STOCK MAIN PCB
(VERSIONS 2 & 3)
Copyright © 2008 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, 6V6 Mod and Mercury Upgrade are trademarks of Mercury Magnetics.
Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
Note: This is a reference diagram. To date, Epiphone has released 3 versions of the Valve Jr. This diagram shows the Main PCB of
Versions 2 & 3. The value changes from Version 2 to 3 are indicated in RED. Also note that Version 3’s PCB is DARK BROWN and
not GREEN in color.

20 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.
T7 T8 T9
T3
V2
V1
T10 T11
T12
GND
C6
C9
C7
C8
T1
T2 D3
T4
T5 R10
R11
T6
B1
C12 D4
D1 D2
IN
G
IN S10 G
VALVE JUNIOR
VER051122
HBO1570
9
8
7
6
5
4
3
2
1
1
9
8
7
6
5
4
3
2
1
1
R12
R14
C3
C5
JP3
C4
R2
R15
R5
R4
R3
C1
R13
R1
R8
JP1
JP2
R9 R6 R7
C2
C11
MAIN PCB PREP SEQUENCE:
1. Remove clips (T1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 11 & 12).
2. Remove rectifier (B1).
3. Remove capacitors (C4 & 12).
4. Remove resistors (R1*, 7, 8*,
9**, 10, 11 & 12).
*Remove for Version 2 PCBs.
Do not remove for Version 3 PCBs.
**Remove for Version 3 PCBs.
Do not remove for Version 2 PCBs.
5. Make 5 trace cuts as indicated.
6. Drill new 5/64” holes as
indicated (holes 1 to 6).
7. If you will be installing the
6V6 Mod then enlarge holes
7 & 8 with 1/16” bit.
8. Add 2 buss wire jumpers
as indicated.
Hole 1 Hole 2 Holes 3 & 4
Jumper 1
Enlarge hole 7
Jumper 2
(before soldering, remove
lacquer to reveal copper trace)
Trace cut 1 Trace cut 2
Trace cut 3 Trace cut 4 Trace cut 5
Holes 5 & 6 Enlarge hole 8
VERSION: 05-09-06 (original)
6V6 REV. 04-09-10 (updated)
www.MercuryMagnetics.com
www.Amp-Exchange.com
Copyright © 2008 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, 6V6 Mod and Mercury Upgrade are trademarks of Mercury Magnetics. Epiphone is a registered trademark of Gibson Guitar Corp. or its subsidiaries. Mercury Magnetics is not affiliated with Gibson Guitar Corp.
Valve Jr.
VERSION 2 & 3 MAIN PCBs