Welcome to the
Epiphone Valve Junior Amplifier Tutorial Website.
Please note that the information contained here is not owned by this web site; owner and has no implied guaranties.
Many people have contributed to the information here, credit will be give to the author if it is known.
This is a simple static page to get you on your way with the Epiphone Valve Junior Guitar Amplifier
PLEASE: Use the Forums for current issues and discussions found at:
http://www.gibson.com/products/epiphone/forum/toast.asp
http://www.sewatt.com
http://www.valvejunior.com
Wonder what the good voltages are in a Valve Junior
Click this link: http://home.graffiti.net/valvejunior101/Voltage.html
HERE is a spread sheet to caclculate the power dissipation: http://home.graffiti.net/valvejunior101/vjr-bias-calculator-master.xls
Explanation of what the various components do from S2 amps
http://www.s2amps.com/docs/vj_kit_inst.pdf
Reference for stock vs modified values for components
http://turretboards.com/valve_junior_page.htm
First version VJrH schematic
http://i166.photobucket.com/albums/u103/cgil155/epi_vjh_schem_stock_144.jpg
Second version VJrH schematic (June 2007 release)
http://i166.photobucket.com/albums/u103/cgil155/EVJr_schematic_V2b.jpg
S2 Amps VJr upgrade slideshow
http://s2amps.phanfare.com/album/91114#imageID=4728384
SEwatt Epi VJ Mods repository and the legendary Epiphone Valve Jr. monster thread. Plan on spending a lot of time living and learning here.
http://www.sewatt.com/forum/36
How to bias a valve junior
http://www.diycustomamps.com/valvejunior.htm#vjbias
Bias calculator using an Excel spreadsheet
http://www.sewatt.com/files/sewatt/sewatt/files/vjr__bias_calculator.xls
Great tech info from general electronics formulas on down to the nitty gritty particulars of tube amps.
http://www.aikenamps.com/
http://www.sengpielaudio.com/Calculations03.htm
http://ax84.rru.com/FAQs/general.html
http://www.duncanamps.com/technical/ampclasses.html
Everything you wanted to know about tubes but were afraid to ask
http://www.vacuumtube.com/FAQ1.htm
http://www.kbapps.com/tubes.html
Resistors in parallel calculator
http://www.electronics2000.co.uk/calc/calcrsp.htm
Name that resistor
http://www.breakup.de/resources/resistor.html
Good place to find schematics
http://www.schematicheaven.com
Amp squeals when you roll the volume (and/or MV, and/or tone) up to the top?
Or sizzling noises as the amp warms up and volume drops to nothing?
http://www.gibson.com/products/epiphone/forum/toast.asp?sub=show&action=posts&fid=4&tid=180067
Silver/Gold Mods plus MV info
http://www.gibson.com/products/epiphone/forum/toast.asp?sub=show&action=posts&fid=4&tid=158801
L-Pad Attenuator info
http://www.gibson.com/products/epiphone/forum/toast.asp?sub=show&action=posts&fid=4&tid=175731
12ax7-Rk/Ck chart for tone tweaks
http://aikenamps.com/RC-FHz.htm
Vendors for components
http://www.tubesandmore.com/
http://www.turretboards.com/valve_junior_page.htm
http://www.stf-electronics.com/Page0002.Html
http://tubestore.com/modkits.html
http://www.tedweber.com/
http://www.hammondmfg.com/125SE.htm
http://www.angela.com/catalog/transformers/Hammond_Transformers.html
http://www.mouser.com/index.cfm?handler=home
http://www.hoffmanamps.com/
http://www.s2amps.com/products.html
Here's the annotated schematic from 18watt.com's VJr repository. This should help you find your way around in there.
[IMG]http://i166.photobucket.com/albums/u103/cgil155/epi_vjh_schem_stock_144.jpg[/IMG]
And annotated pictures, also from 18watt!
[IMG]http://i166.photobucket.com/albums/u103/cgil155/mvc-019f.jpg
[IMG]http://i166.photobucket.com/albums/u103/cgil155/mvc-018f.jpg
[IMG]http://i166.photobucket.com/albums/u103/cgil155/mvc-017f.jpg
[IMG]http://i166.photobucket.com/albums/u103/cgil155/mvc-020f.jpg
[IMG]http://i166.photobucket.com/albums/u103/cgil155/evjrstock_pcb3.jpg
[IMG]http://i166.photobucket.com/albums/u103/cgil155/evjrstock_pcb1.jpg
This list is very helpfull when ordering parts from mouser.
Recommended minimum mods from 18Watt.com
Mouser.com stock #
Description 1 Description 2
R1 1meg 660-MF1/2CL1004F KOA Speer 1/2Watt Me 1Mohms 1% 50PPM
R2 10K 660-MF1/2CC1002F KOA Speer 1/2Watt Me 10Kohms 1% 50PPM
R6 shorted out (also 100k or 470k works well here)
R7 replaced with 500K or 250k pot, for Gain control or 31JA505-F Taiwan Alpha 16mm Ca Audio 500K (from Greg J)
R7 91k 660-MF1/2CL9092F KOA Speer 1/2Watt Me 90.9Kohms 1% 50PPM
R8 1k or 1.5k 660-MF1/2CL1501F KOA Speer 1/2Watt Me 1.5Kohms 1% 50PPM
(The S2 document also states that 820ohm or 620ohm works here as well)
R9 620-820 ohms 660-MF1/2CL6800F KOA Speer 1/2Watt Me 680ohms 1% 50PPM
(The S2 document also states that 820ohm or 620ohm works here as well)
R14 240 ohms 594-5083NW240R0J Vishay/BC Components 2watts 240ohms 5%
(some have found that R14 has to be ajusted from 240 to 270 depending on the voltages in you amp)
1K 2W EL84 pin9, grid trace (1W to 3W will work) 71-CPF2-F-1K-E3 2W Flameproof Metal Film 2watts 1Kohms 1%
(2.2k and 2.7k have also been used as a screen grid resistor, as noted on aother thread, anything above 500 will start to change the sound of the amp)
C3 3.3uf 647-UVR1H3R3MDD Nichicon Radial Alum 50V 3.3uF 5X1 (or anything between 2uF to 4.7uF to your taste)
C4 3.3uF 647-UVR1H3R3MDD (or anything between 2uF to 4.7uF to your taste)
C5 1000uF 647-UVR1H102MHD Nichicon Radial Alum 50V 1000uF 12.5X25
Must have for the correct B+ voltages: R10 (see the voltages page link)
R10 1K 3W (1.2k also works well here, 3watt or 5watt will work)
Optional Parts
T2 Standby switch 103-0132-EVX Mountain Switch Togg ON-OFF TOGGLE SWITCH
Chickenhead knob w/set screw(for match w/vol-gain order 2) 5164-2300A Davies Knobs BLK NO-LINE 1/4X1/2
Hammond 125DSE Output Transformer http://www.stf-electronics.com/Page0009.Html
This link is for those that want to know more about why things are: http://www.tpub.com/content/neets/14178/
