Thicknening up Valve Junior tone

[guitarcam123]

I'm planning to open up my valve junior head soon and do a few mods to it. Can someone recommend me some mods which I can perform on it to thicken up the tone and add a bit more gain?

Also while I'm at it, will the following "tone stack" work properly if I install it or are further modifications to the circuit required?


Cheers

[Steve Conner]

Plug it into a 4x12, that'll thicken it up nicely!

The tone stack will work, but if you want more gain, adding a tone stack is the wrong thing to do: all tone stacks have insertion loss.

If it were me, and I wanted to mod a VJr, I'd clip out the cathode bypass capacitor on the second stage, replace the first stage one with 1uF, replace the first stage cathode resistor with 1.5k, and remove the two 1Meg fixed resistors around the volume control (re this schematic: http://3.bp.blogspot.com/_iQOTeAgvE8...BSchematic.jpg)

Season to taste with a bright cap on the volume control.

This might not "thicken" it but it would give more usable gain, a tighter distortion with less fuzzing and farting. You could also insert your tone stack in place of the volume pot after the above mod: losing the two 1Meg resistors might compensate the insertion loss.

A larger output transformer might be worth considering too. The stock VJr one isn't that impressive. A Hammond or Edcor might give you a bit more volume and bass. But at the end of the day, if you want it to really punch you in the gut, that's not going to happen. It's a 3 watt amp.

[mooreamps]

Yes, add a 6V6 in parallel with the EL-84 power tube. Both the stock O/T and power transformer can handle the extra load. The total output power would still be around 5 to 6 watts ; given the load current rating of the power transformer.. Yes you could also swap the O/T for a Hammond or something.. That does tend to open up the tone some...

-g

[guitarcam123]

Its actually got this 15W O/T installed now as I recently burnt out the original. I'll have a look at installing a 6V6 in parallel with the El84. What sort of tonal changes should I expect?

I'm not to concerned about losing a bit of gain from the tone stack as I'm going to do some other mods which have been recommended such as replacing R7 with a 100k pot for a "gain control" and replacing R6 with a 320k resistor which is supposed to make it sound more "marshally" which will hopefully compensate for the loss in gain from the tone stack. I'm mainly just trying to get a thicker, more bassier tone from the amp.

[mooreamps]

Its actually got this 15W O/T installed now as I recently burnt out the original. I'll have a look at installing a 6V6 in parallel with the El84. What sort of tonal changes should I expect?

.

When I did it on my first 5 watt engineering prototype, it caused quite the stir on the other internet forums. I began to start seeing others trying to reverse engineer the concept after seeing some of the uploads I posted ; and backdating some schematics saying they were doing before I was.....

Here is a clip of my 5 watt prototype ; much like what the kind of mod you appear to be writing about.... In this clip ; Mike Osborn plays through my 5 watt engineering prototype on stage at the Quarternote in Sunnyvale ; thru my backloaded 2x12 cab... As you will see, 5 watts thru the right speaker cab is pretty gigable... Of course this amplifier has my electronic power brake for those "Overdriven" tones ; which you may not get unless you put a pedal in front of your amp ; like a Mesa V-Twin or something...

YouTube - Model gm-5 ; 5 watt guitar amplifier #3


-g