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Old 02-29-2008, 08:39 PM   #1
SomeoneYouKnew
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the Epiphone Valve Junior Resource thread

This thread is a Work in Progress.

For links to many other great threads, check out the GB&C Central Hub.

The VJ is a great little tube amp that was introduced at an unheard of price.
It has limited features, but good tone, and is a modderís dream.
Even though its price has increased, itís still a great value for the money.
Itís simplicity makes it easy to understand and mod.
Similar amps have now appeared in the marketplace.
That comes as no surprise.
Small tube amps are here to stay.


Objective:

To create a collection of data for repair and modifications for the Epi VJ.

Perhaps this will also expand into other similar 5 watt amps,
like the Blackheart, Harley Benton, Champ, and Champion
but for now, just the VJ.

Users are encouraged to submit mods theyíve used, or are interested in trying.
And links to appropriate sites or useful threads found on UG.


All useful info will be absorbed into the OP(s) of the thread.

If worthy, a link to this thread will be added to the tutorial thread.



Resources:

Post #2 - Identification/schematics for the differing versions of the stock VJ as it evolved.

Post #3 - Links to VJ project threads on UG and VJ mod pages elsewhere on the net

Post #4 - Analysis of modifications / component values / effects on the character of the amp.


The first 4 posts will be edited and updated, as needed, periodically.
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Quote:
Originally Posted by Jackal58
I release my inner liberal every morning when I take a shit.
Quote:
Originally Posted by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.

Last edited by SomeoneYouKnew : 02-29-2008 at 08:43 PM.
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Old 02-29-2008, 08:39 PM   #2
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Identification:

Version 1:

Schematic


(combo only)

1 - AC filaments. (more hum)
2 - One output jack (4 ohms)
3 - Pinstripes across the center of the front panel.
4 - Printed board has 7 mounting screws. Board color is GREEN.
5 - Speaker: Weber Ceramic Signature 8
6 - Tubes: Sovtek ???


Version 2:


Schematic


(We need pics of version 2 amps)

1 - DC filaments.
2 - Output jack 1 (4 ohm) (notes - 1&2)
3 - Pinstripes across the top of the front panel.
4 - Printed board has 6 mounting screws. Board color is GREEN.
5 - Speaker: Weber Ceramic Signature 8 (note -2)
6 - Tubes: Sovtek (note -2)



Version 3:


Schematic


Head


Combo

1 - DC filaments. (less hum)
2 - Three output jacks (4/8/16 ohms)
3 - Pinstripes across the top of the front panel.
4 - Printed board has 6 mounting screws. Board color is BLACK.
5 - Speaker: Eminence Lady Luck 8
6 - Tubes: EHX 12AX7 / JJ EL-84 (note -2)




Component Values Comparison Chart
Refer to Version 3 schematics for mark
Code:
Component Mark V3 V2 V1 Grid bias 1 R1 1Meg 68k 68k Grid Stopper 1 R2 68k 68k 68k Plate 1 R3 1Meg 100k 100k Cathode 1 R8 1k5 2k2 2k2 Cathode Byp 1 C4 22uF/50v 22uF/50v 22uF/50v Local shunt C11 1uF/400v 22uF/450v none Coupling cap 1 C1 .022uF/400v .022uF/400v .022uF/400v Vdivide T R6 1Meg 1Meg 1Meg Vdivide B R7 1Meg 1Meg 1Meg Volume pot R6 1MegA 1MegA 1MegA Plate 2 R3 100k 100k 100k Cathode 2 R9 1k5 2k2 2k2 Cathode Byp 2 C3 22uF/50v 22uF/50v 22uF/50v Coupling cap 2 C2 .022uF/400v .022uF/400v .022uF/400v Grid bias 3 R5 220k 220k 220k Grid Stopper 3 R15 1.5k 1.5k 1.5k Output Transformer - OT-VJ5 Power Transformer - PT-VJ5 Diodes (B+) x4 - 1N4007 1N4007 1N4007 First Filter C6 22uF/450v 22uF/450v none Drop resistor R10 220R/2w 100R/3w none Plate Cap C9 22uF/450v 22uF/450v 22uF/450v Bleeder resistor R11 220R/2w 75R/3w none Screen resistor R12 4k7/3w 4k7/3w 4k7/3w Screen Cap C7 22uF/450v 22uF/450v 22uF/450v Preamp resistor R13 10k 10k 10k Preamp Cap C8 22uF/450v 22uF/450v 22uF/450v Hum balance x2 - none none 100R Filament Bridge B1 8amp 8 amp none Filament Cap C12 4700uF/16v 4700uF/16v none




Notes: (contributors)
1 - info provided by rafarquhar
2 - info provided by MrCarrot
3 - info provided by the_random_hero
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Quote:
Originally Posted by Jackal58
I release my inner liberal every morning when I take a shit.
Quote:
Originally Posted by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.

Last edited by SomeoneYouKnew : 04-23-2008 at 05:28 PM.
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Old 02-29-2008, 08:40 PM   #3
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Links


UG links:

Kerry's Valve Junior Mods
(call1800ksmyazz's version 2 head)

Kerry's Valve Junior Mods 2!
(call1800ksmyazz's version 3 head)

Valve Jr Mods, Finally
(MrCarrot's version 2 head)

kurtlives Valve Jr. Moddin


Net links:


http://www.valvejunior.com/
(V1 includes Light bulb Attenuator)

http://duhvoodooman.com/VJr/VJr_mods.htm
(V1 includes a Brightness Switch)

http://www.euthymia.org/DIY/VJmods.html
(V1 includes Output Impedance Switch)

http://www.diycustomamps.com/valvejunior.htm
(includes Tweed style Tone Control and Biasing the EL84)

http://users.telenet.be/svokke/valv...nior%20mods.htm
(V1 Decreasing hum WITHOUT changing to DC heating)

http://members.optusnet.com.au/eyes...j_mods_3/vj.htm
(V1 adding a second 12AX7)

http://www.sewatt.com (note 2)
(amp forum - requires membership to view)

Chart of component values for several mods (note 3)






Comparison to other Amps::

VJ schematic adapted to Gibson GA-5 values.

*Click on image for larger version*




VJ schematic adapted to Blackheart BH5 values.

*Click on image for larger version*





Basic Troubleshooting


I have chosen the V2 version for this discussion because the diagram I have already has typical voltages listed on it. Iím asking anyone who has a V1 or V2 to make similar measurements so I can update the drawings.



Most likely causes of failures:
Tubes
Resistors (Open or higher resistance than normal)
Capacitors (Shorted or resistive)
Poorly soldered joints (resistive / poorly conductive)
Carbon tracking / solder bridged between foil traces

1 - Voltage drop across cathode resistors.
This is usually my first stop during troubleshooting. A slight variance between the reference values and the measured values is usually nothing to worry about. But a large variance indicates a problem. It wonít tell you exactly what the problem is, but itís a good start.

If the voltage measured across the cathode resistor is much higher than the reference value, the resistor itself may be open or have a higher resistance than normal. The higher voltage could also mean too much current is flowing in the tube. One possible cause is a shorted or resistive coupling cap from the previous stage. The control grid in these amplifier stages is referenced to ground. If there is a conductive path from the previous stage, this will bias the grid to a positive voltage. This is a particularly ugly situation. The control grid will draw current. It is a fine, delicate structure that was never intended to do that. The tube may be damaged when this happens. At the very least, the positive bias on the grid will cause the tube to conduct heavily. This will cause severe distortion, or even put the tube so far out of normal operating conditions that no change in plate current will occur when the grid voltage changes because of the input signal. ie: No sound.

If the voltage measured across the cathode resistor is much lower than the reference value, the cathode bypass capacitor may be shorted be resistive. Or there may be a solder bridge between foil traces or carbon tracking. If everything is right with the cathode circuit, the voltage might still be low because of an open (or much higher resistance than normal) plate resistor.

2 - Plate voltages
In an amplifier that is working properly, the same amount of current is flowing in the plate resistor as in the cathode resistor. So the voltage drop across the plate resistor is equal to that current times the resistance. This will be the difference between the supply voltage (3) and the voltage measured between the plate and ground. This is one more place where you can determine the source of the problem when things donít add up.

If the plate voltage is low (or the voltage drop across the plate resistor is high) this either means there is too much current in the tube, or the plate resistor is open or has a higher than normal value.

If the plate voltage is high (or the voltage drop across the plate resistor is low) this either means there is too little current in the tube, or the plate resistor has been shorted by a solder bridge or carbon track.

3 - Supply voltage
A low supply voltage can be caused by too much current being drawn, or by a failure in the power supply. A high supply voltage can be a symptom of too little current being drawn. The supply for the preamp tubes is not regulated, and is fed by a resistor. The amount of current drawn by the tubes greatly affects the supply voltage. Although there may be a problem with the power supply, such as a shorted or resistive filter capacitor, or a burnt series resistor in the PS, itís more likely a low voltage supply voltage is a symptom of too much current being drawn.

USE YOUR EYES.
Look for poorly soldered joint, solder bridges, carbon tracking, burnt resistors, and swollen filter capacitors. You can confirm your suspicions by making resistance or voltage measurement. But often your eyes alone will lead you to the problem.

Faulty coupling capacitors rarely show any external signs of damage. Sorry, but your eyes wonít help you there.
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Quote:
Originally Posted by Jackal58
I release my inner liberal every morning when I take a shit.
Quote:
Originally Posted by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.

Last edited by SomeoneYouKnew : 04-23-2008 at 05:27 PM.
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Old 02-29-2008, 08:41 PM   #4
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Modifications


General Modding Advice:

Some modifications will be replacements of components with the same values, but the quality of the parts are better.

Why didnít they use better quality parts in the first place?
Put yourself in the shoes of the company making the product.
In most cases itís a matter of a few cents difference.
But those pennies add up.
If you can save a total of $10 in parts cost on each amp,
And you sell 100 thousand amps,
Youíve just saved a million dollars!

Donít go cheap.
Youíre only modding one amp at a time.
The savings are x1 not x100k.

Don't waste money on hype.
Get good quality parts for reasonable prices.
$1 each for film caps -vs- $.29 for ceramic is a no-brainer. Film caps, ftw.
$20 a piece for paper/oil caps gets ridiculous.

Do clean work.
If youíre going to spend the time and effort to do it,
Spend the little extra time it take to get it right.
Make sure the work is properly done and looks good, too.



Individual Modifications:


The power supply is the most neglected area for modifications
But it shouldnít be.
This is a great place to improve the performance and alter the character of any amp.
  1. - Upgrade the filter caps to ďstiffenĒ things up.

    1. - The output stage of an SingleEnded amp will transfer more noise from the Power Supply than a Push-Pull amp.

    2. - The filter caps in a VJ are a measly 22uF. Increasing the size will make a huge difference in performance.

    3. - Donít get ridiculous. The caps have to charge, initially. 40uF makes a big difference. The bigger they are, the more strain on your rectifiers and PT, during startup. I donít recommend going over 100uF without adding some series resistance to lessen the initial current.

    4. - Adding small capacitors (~.1uF) in parallel with the electrolytics helps with spike noise. Large electrolytics have internal inductance in series with them. They are less effective with high frequencies/sharp edged waveforms, than you would expect.

  2. - Add series resistance to increase sag, decrease voltage, and improve filtering.

  3. - Bias the heaters to a positive potential. This will stop filament emission to the cathode. Very effective with AC filaments. Not as important, but still a nice touch to add to DC filament supplies.

  4. - Upgrade the diodes and/or add de-spiking caps. The VJ uses 1N4007 diodes. Cheap and effective. But the slow switching times cause spikes. Add de-spiking caps and/or replace the diodes with UF4007s.


Note: The image below is not a drawing of a VJ power supply.
I chose to use it, because it already had the de-spiking caps on it.


... more in a few days.
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Quote:
Originally Posted by Jackal58
I release my inner liberal every morning when I take a shit.
Quote:
Originally Posted by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
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Old 02-29-2008, 08:47 PM   #5
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Mad props man. May actually direct me into buying one just for modding purposes.
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Old 02-29-2008, 09:44 PM   #6
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Great thread idea, SYK. You talked me into getting one to practice tube amp modding (when I get the cash). :p
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Old 02-29-2008, 11:39 PM   #7
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You might want to know!
There's a version 2 of the combo. Significant changes from version one to two are that the stripe across the front of the chassis is moved from going across the center to being on the top. The amp has DC filaments and it also only has a single four ohm tap in the rear.
(I own it. I'm pretty sure that it has DC filaments, because mine does not seem to have much hum except for a very tiny bit when cranked 100%.)

There was also a really easy chart somewhere that told you which components to replace with what to make the amp sound more like a Vox or Fender or a Marshall, but I forget where I saw it.
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Old 03-01-2008, 01:33 AM   #8
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Quote:
Originally Posted by rafarquhar
You might want to know!
There's a version 2 of the combo. Significant changes from version one to two are that the stripe across the front of the chassis is moved from going across the center to being on the top. The amp has DC filaments and it also only has a single four ohm tap in the rear.
(I own it. I'm pretty sure that it has DC filaments, because mine does not seem to have much hum except for a very tiny bit when cranked 100%.)

There was also a really easy chart somewhere that told you which components to replace with what to make the amp sound more like a Vox or Fender or a Marshall, but I forget where I saw it.
Yes! Thanks.
These are exactly the kinds of things that will help a great deal.

Is the cabinet the same as version 1, but the pinstripe on the front of the chassis is moved up?

Is the INPUT jack on the front, in the same location as version 1 or version 3?

If you happen to run across that chart again, be sure to drop a link on this thread.
I have several thoughts on voicing this amp, through altering values of cathode capacitors, coupling caps, and biasing. This in addition to adding a tonestack. It will be interesting to see if the values they recommend are the same as what I have in mind.

Thanks,
SYK
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Originally Posted by Jackal58
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Quote:
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Old 03-01-2008, 06:16 AM   #9
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Nice thread.

I've got a small modding thread in my sig.. But I've done a hell of a lot of mods to my V2 combo in the year I've owned it... I'd say I knew a bit about it

Also, I HIGHLY recommend the www.sewatt.com forum for all this VJ modding. Loads of resources and helpful minds on there.

Edit: And the V2 Combo has the Weber Sig ceramic 8 also. Sovtek tubes, too. Afaik all the V3s come with EHX/JJ tubes.
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Last edited by MrCarrot : 03-01-2008 at 06:55 AM.
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Old 03-01-2008, 11:56 AM   #10
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Ill post my Ulimate VJ Mods later...I am still working on mine and tweaking.
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Old 03-02-2008, 11:03 AM   #11
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Bumpety.

Yeah, I'm considering dropping a 12AU7 in the preamp position, to experiment with getting (next to) no preamp gain, purely poweramp.
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Old 03-02-2008, 11:11 AM   #12
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Hmm I have two 12au7 on me at the moment. I think I will try this.

This is a straight swap right?
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Old 03-02-2008, 11:16 AM   #13
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Yup. Just swap it for the AX.

Tell me what you think of it. It'll be quieter btw, so expect that...
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Old 03-02-2008, 11:30 AM   #14
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Ahh alright....I am going to try now.
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Old 03-02-2008, 11:43 AM   #15
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hmmm.....

So with a 12au7 my output it significantly reduced. I had to set both the pre and master volume at 3 o'clock to get the volume to hear my self clearly. It was a nice clean tone though, smooth, Fenderish.

With the 12au7 though the amp could not be pushed into saturation. With gain and all the volumes maxed and R6 at 220K it was still squeaky clean....

It was worth a try though.
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Old 03-02-2008, 08:20 PM   #16
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I have a switch on R6 to select either a 1.2M resistor or a 220K resistor. I would like the 1.2M side to be brighter and crisper. I would the 220K side to be ballesy with nice mids.

Now I tried a small cap in parallel with the 1.2M and that gave me a nice bright sound. But it seemed to carry over into the 220K side aswell.

Ideas, help?
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Old 03-02-2008, 09:22 PM   #17
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The chart of mods.
Thanks for making this thread, I'm still considering dropping $200 on this sucker.
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Old 03-02-2008, 11:06 PM   #18
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I just bought one on ebay. I'll be watching this thread closely. I think its a V1 though, i just realized.
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Old 03-02-2008, 11:11 PM   #19
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^saftey first
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Old 03-02-2008, 11:14 PM   #20
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Pretty sure I know the answer to this, but who it goes: The resistors in the VJ are all 1/2 watt correct? So I can NOT use a 1/4th watt resistor, regardless of spot in the circuit right (R1 is what I'm looking at) as I assume the current is consistent through out the PCB and will fry it?
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