Mystery amp, what is it?

[psychic fuzz]

Hey! This is my first post here (I think). I have this amp on another site some of you might have seen but figured I'd share it here.

Bought this amp on whim the other day online, I'm hoping someone can help me pinpoint what circuit this is based on and what's going on here.

What I do know so far from my research is that all the transformers seem to have been used in Super Reverbs, 50w OT. A member of another forum suggests it's the Normal channel of a AB763 possibly. With a MV added of course.

2x 6L6
2x RCA 7025/12AX7
1 GZ34s

Orange caps are "Torres". I'm thinking this is an early mid 2000's build.

Observations from playing: Too much bass and super loud, even with gain dialed low. Very difficult to dial in any overdrive at reasonable levels.

What I'd like to do is reduce the bass, increase the gain so the master is a bit more usuable. And eventually do some D-style mods to it. I'll start another thread eventually in the correct area once I figure out my plan.

Any insight is greatly appreciated!

FYI - My experience building is mostly basic stuff like building pedals, amp mods and cap jobs. I'm dangerous with an iron but my technical electronic knowledge is a still work in progress. I may ask a lot of questions that may seem obvious to others. Just a heads up!

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[Stevem]

To start with if you want less bottom replace those two .1 Uf caps at the end of the board with .022 Uf caps at 630 volt.

[Stevem]

To start with if you want less bottom replace those two .1 Uf caps at the end of the board with .022 Uf caps at 630 volt.

[maxkracht]

That ground lug is wild! You might try adding global negative feedback to tighten things up a bit? You might also want to change the master volume to post phase inverter if you add a negative feedback loop.

[psychic fuzz]

To start with if you want less bottom replace those two .1 Uf caps at the end of the board with .022 Uf caps at 630 volt.

The two .1uf on the right side of board? thanks!

[psychic fuzz]

That ground lug is wild! You might try adding global negative feedback to tighten things up a bit? You might also want to change the master volume to post phase inverter if you add a negative feedback loop.

I know it’s insane! Also Per someone else suggestion I’m going to rewire the ground switch and delete the caps there. No idea why they included it

[sluckey]

A member of another forum suggests it's the Normal channel of a AB763 possibly. With a MV added of course.

I agree.

[psychic fuzz]

*

[psychic fuzz]

Did a quick bias probe and getting around 440v-ish plate voltage.

Using master volume and cranking gain, it's a kind of an unpleasant tweedish/bassman distortion. (Not the nice expensive vintage kind). I think some tweaks to the EQ will help that.

You can dial in some decent fuzzy tones, but bass needs to be very low and mid all the way down and treble around 2.

Are these circuits candidates for "D-style" stuff or am I better off tweaking without that in mind.

[Phil_S]

Stuff should not be grounded on transformer bolts, particularly not the mains ground. If you aren't able to solder directly to the chassis, drill for a new bolt anywhere near where the mains ground enters the chassis. It is a good practice to make the mains ground wire long enough that, in case the power cord is getting yanked out, the ground is the last one to go.