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#1
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 modder’s dream.
Even though its price has increased, it’s still a great value for the money.
It’s 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 they’ve 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.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
Last edited by SomeoneYouKnew at Feb 29, 2008,
#2
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
[B]Component		Mark	V3		V2		V1[/B]

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
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
Last edited by SomeoneYouKnew at Apr 23, 2008,
#3
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/valve%20junior%20mods.htm
(V1 Decreasing hum WITHOUT changing to DC heating)

http://members.optusnet.com.au/eyes.only/vj_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. I’m 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 won’t tell you exactly what the problem is, but it’s 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 don’t 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, it’s 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 won’t help you there.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
Last edited by SomeoneYouKnew at Apr 23, 2008,
#4
Modifications


General Modding Advice:

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

Why didn’t they use better quality parts in the first place?
Put yourself in the shoes of the company making the product.
In most cases it’s 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,
You’ve just saved a million dollars!

Don’t go cheap.
You’re 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 you’re 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 shouldn’t be.
This is a great place to improve the performance and alter the character of any amp.

  • - Upgrade the filter caps to “stiffen” things up.



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


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


  • - Don’t 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 don’t recommend going over 100uF without adding some series resistance to lessen the initial current.


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


  • - 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.


  • - 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.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#7
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.
Main gear (For complete list, see profile):
Epiphone Les Paul Standard Plain-top
Basswood Telecaster, 2 single-sized HB's, both split.
Epiphone Valve Junior
B-52 AT-412 Cabinet
Oh, and I have a Squier VM Jazz Bass too.
#8
Quote 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
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#9
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.
The Laney Thread are big and clever. No exceptions.
Last edited by MrCarrot at Mar 1, 2008,
#11
Bumpety.

Yeah, I'm considering dropping a 12AU7 in the preamp position, to experiment with getting (next to) no preamp gain, purely poweramp.
The Laney Thread are big and clever. No exceptions.
#13
Yup. Just swap it for the AX.

Tell me what you think of it. It'll be quieter btw, so expect that...
The Laney Thread are big and clever. No exceptions.
#15
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.
#16
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?
#17
The chart of mods.
Thanks for making this thread, I'm still considering dropping $200 on this sucker.
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#18
I just bought one on ebay. I'll be watching this thread closely. I think its a V1 though, i just realized.
Call me Roche.

Quote by Dyers
wut is a luthier? im assuming it has to do with the luthern church
#20
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?
#23
Thanks guys; didn't want to break open my pack of 1/2th watters if I don't need them. I thought about doing the octal tube mod, but want ot cut my teeth with the Gain and High Input Jack mods.
#24
Quote by the_random_hero
The chart of mods.
Thanks for making this thread, I'm still considering dropping $200 on this sucker.
Thanks for the link, Drew!
I should make a similar chart to compare the values of the stock V1, V2, and V3 components.
The V3 already has several of the "mods" in the stock version.

Why so much for the VJ in Oz? They only cost $150 for the combo, $130 for the head in the US. Do they hit you that hard on shipping, or is there an import tax that raises the price so much?


@ don't eat baby,
The V1 is still a good amp. A few Mods, and it rocks!

@ kurtlives91 & MrCarrot,
12AU7 is a huge step down in gain. Maybe try a 12AT7 or 12AY7?

... and are you using a SPST to parallel the resistors when you use the 220k?
or are you using a SPDT to select 220k or 1.2meg?
Drawing?

Quote by CJRocker
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?
Not to worry, CJRocker. The current isn't the same throughout the PCB. And it isn't just the current, but the voltage drop across the resistor that determines the power dissipated by the resistor.

1/4 watt resistors will be just fine for many of the places in a VJ. In fact, unless you change the value of R3 to 1 Meg, you can use 1/4 watt resistors for all the resistors in the preamp section. I still prefer to use 1/2 watt for the plate resistors, though, even though they don't dissipate that much power.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#26
Quick question. So if i understand power supplies correctly, all i need to do to convert from AC to DC and remove the hum is add a bridge rectifier and an electrolytic right? and what value for the cap, 470 uf, 1000uf?
Also, where do you guys buy your parts from?
Call me Roche.

Quote by Dyers
wut is a luthier? im assuming it has to do with the luthern church
#27
Quote by don't eat baby
Quick question. So if i understand power supplies correctly, all i need to do to convert from AC to DC and remove the hum is add a bridge rectifier and an electrolytic right? and what value for the cap, 470 uf, 1000uf?
Also, where do you guys buy your parts from?


I was told the rule of thumb for calculating the capacitor is 2200uf/amp of current drawn. If you twist the heater wires, you could get away with 470uf, but I'd go up to 1000uf just to be sure. Anything above that is getting to the overkill level, from what I've read/been told.
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#28
^
Hey Drew, this is an amp, not a pedal. So size isn't an issue. Only cost.
And 4700 uF is only a few pennies more than a 1000 uF.

The value of the cap on Version 3, is 4700 uF / 16 volt.
Just click on the Version 3 schematic to see the large drawing.

I get most of my parts locally, but I've ordered a few things through Newark Electronics.
Mostly for other things that had nothing to do with Guitar amps. They do very fast shipping.
I hear Mouser is good, too.
For amp specifics parts, Here's a quote from s.r.v.'s Ultimate Pedal building thread.
Quote by s.r.v.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
Last edited by SomeoneYouKnew at Mar 3, 2008,
#29
All my mod points are using 1/4w resistors, that's the preamp ones, cathode spots and input ones and the EL84 Grid Resistor. Apart from a Carbon Comp 1/2w for the extra harmonic dirt at R4 it's all fine..
The Laney Thread are big and clever. No exceptions.
#31
I don't think it has a voltage regulator? I've not seen one in it...

And on another note I was considering experimenting with changing the preamp section to be the same as the Marshall 18w Normal Channel, minus tone control, although I may add a tone if it turns out well.
The Laney Thread are big and clever. No exceptions.
#32
Another stupid question: When it says to "jumper" across R6, does that mean remove R6 and replace it with a jumper or something else?
#34
Quote by kurtlives91
Does the VJ use a LM7812 for a voltage regulator?


"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#35
Quote by kurtlives91
Yes remove R6 and put a wire across it.

Thanks again. Kind of new at this of course Had to get a new soldering gun (the tip and the screw that held it in was coming apart due to being 20 years old...), and I don't feel like doing it tonight, but tomorrow it's going to rain so I'll have plenty of time to work.
#36
Quote by the_random_hero
I was told the rule of thumb for calculating the capacitor is 2200uf/amp of current drawn. If you twist the heater wires, you could get away with 470uf, but I'd go up to 1000uf just to be sure. Anything above that is getting to the overkill level, from what I've read/been told.



Quote by SomeoneYouKnew
^
Hey Drew, this is an amp, not a pedal. So size isn't an issue. Only cost.
And 4700 uF is only a few pennies more than a 1000 uF.

The value of the cap on Version 3, is 4700 uF / 16 volt.
Just click on the Version 3 schematic to see the large drawing.


Wait, so which would be better? 1000uf or 4700 uf? Cause i have a few 1000uf laying around, so if i don't need 4700uf that would be nice.

Also, i'm adding a 100uf fliter cap in parallel with the other filter caps. How much tonal difference can the type of cap make? In other words, would it be worth it to use a Sprague Atom, etc. or just any old filter cap?
Call me Roche.

Quote by Dyers
wut is a luthier? im assuming it has to do with the luthern church
Last edited by don't eat baby at Mar 3, 2008,
#38
Ok, but to answer my other question, how much does brand matter?
Call me Roche.

Quote by Dyers
wut is a luthier? im assuming it has to do with the luthern church
#40
Ok thanks.
Call me Roche.

Quote by Dyers
wut is a luthier? im assuming it has to do with the luthern church
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