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Modifying the Valve Jr.

I got my version three (V3) Valve Jr. head way back in late October 2007. Since then I have been playing with it and modding it off and on. I originally wanted to voice it to be like a Fender. After building and finishing my Vibro Champ though I decided I want to give it more balls and gain. So I kept what I had done to the amp prior and started doing more Marshall style type mods.

Even when I voiced it to be a Fender it never really worked though. With no tone stack and that EL84 output tube the VJ doesn’t stay clean for long. It also has quite a lot of midrange frequencies because of the lack of tone-stack, this makes it break up quicker and again sound less like a Fender amp. So yeah I did some Fender mods but then I decided I wanted it to sound a bit more "Marshalley" so now my VJ has a bit of both worlds in it. It has that clear sharp Fender tone but it also has a lot of gain and grit.

(All resistors 1/2W carbon film unless otherwise noted)
R1 – 1M (increase input impedance, stock grid leak resistor is too small, makes things dark and muddy)
R2 – 22K
R4 – 100K carbon comp. Why I used carbon comp here… http://www.geofex.com/Article_Folde.../carboncomp.htm
R5 – 220K resistor. Wires go to either side of resistor. Then they go to lugs 1 and 3 of an Alpha 500K pot. Run a wire from lug 2 to the side of R15 closer to the input. Now you got a master volume control.

R6 – This resistor is my gain switch. I use a DPDT (On-On) switch to select between a 320K and 1.2M resistor with a 220pF cap in parallel. This gives me a gainey sound with balls and lots of boost. The other side is much cleaner and brighter. I call this my Fender/Marshall switch. I experimented a lot with the values these are the best in my opinion.

R7 – 39K resistor with 100K pot in series. This is an effectively a gain pot.
R8 – 1.2K
R9 – 1K
R10 – 1K 3W
R14 – 244 ohms 1W
R15 - 6.9K I played with this a lot. It can really affect the Marshall/Fender voicing of the amp.

C1 – 0.0068mF Orange Drop. Makes the tone less harsh. Orange Drops keep things clear and sharp, I used them for the coupling caps (C1 + C2)
C2 – 0.022mF Orange Drop
C3 – 2.2mF (I used these vintage Australian caps here, I really like them) The stock cathode bypass caps (C3 + C4) are 22mF, 2.2mF tightens up the bass nicely.
C4 - 2.2mF (I used these vintage Australian caps here, I really like them)
C5 – 100mF 25V (vintage Sprague)
C6 – C9 – 47mF 450V. This stiffens up the filtering, reduces hum and makes the bass more solid.

I also replaced the stock volume pot which is a preamp volume with a new Alpha 1M pot. I added a tone “tweed” style tone control while at it using a 500pF Silver Mica and a 4700pf vintage mustard cap. I used an Alpha 1M pot for the tone control.

I retubed also, I don’t like Sovtek tubes (like most people). I used JJ/Telsa, I have always liked them and they sound great. I hate EHX tubes…..microphonics bah

I also have drilled a pentode/triode switch so the amp has an output of 5W or 2.5W. After considering it for a while I decided it would be stupid to install the switch. The amp is 5W and I can crank it and it doesn’t hurt my ears and no one complains.

What I have now is a VJ that does not break up as quick as a Marshall voiced VJ. It has solid tight bass when clean or when dirty. This was an issue that took a while to fix and deal with. I always like tight bass and this VJ provides. With no tone-stack it is full of mids. And it also has nice sharp highs, the perfect frequency curve. I get a sharp clear tones when clean or dirty but yet I great a great distortion tone. The Fender/Marshall switch is just amazing. On the Marshall side there is lots of mids and the amp breaks up quickly. When on the Fender side things are crystal clear and it is hard to get the amp to break up. The distortion is thick and full. It is also dead quiet with better quality components in the signal path and new great quality filter caps. It is very versatile with more controls.

Anyways very fun amp with lots of fun controls to play with now. Not bad for a noisy amp that only had a volume control. Great tube amp that probably only cost $200 with all the mods.

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