Take your basic excelsior (schematic) and...

[tubeswell]

... lets start a discussion about how to mod this amp

I see they've included an IRF820 source follower for the trem circuit (+1 for 'them').

Might not be too hard to squeeze in a small tone control pot (in place of the switch) - or a depth control for the trem.

[Bear]

I've been waiting for this to get around. Time to start comparing to classic schematics to get some ideas.

I'd seen a couple different mention of the mosfet but no clear explanation of the precise role. Just googled some amp implementations and it sounds like a pretty useful device to integrate. So used as a CF for a stronger signal to modulate the output bias. Clever.

[tubeswell]

I used (IRF820) source followers on a few trem circuits. It doesn't have any adverse impact on the performance of the trem, and is superior in terms of reliability (compared to modern production tubes) because there's no h-k voltage to worry about.

[DonMoose]

Gonna go look at one of these tomorrow - 13W and a 15" speaker sounds pretty ideal for what I'm after.

Considering, in order of liklihood:
500k pot in place of tone switch,
Concentric pot for trem depth/rate,
Maaaaybe re-do the trem osc to solid state, convert PI to LTPI, Output to fixed bias and trem to bias-wiggler. Maybe (that's a big delta).

[tubeswell]

Yes I think bias-vary trem would be nice with those 6V6s

[Bear]

The tone switch is built in a circuit so close to the 5F11 tone control (or similar tweed Tremolux tone controls) that I would look there or at any popular mods when hunting for values.

[DonMoose]

I picked that one up and ... I kinda like it the way it is. At least for living room cleans.

Now looking for one that's electrically wrecked but cosmetically good so I can try some things - like an ODS preamp with the two top knobs as the masters, and the rest of the controls on the back.