What is this circuit?

[Tonesheriff]

A friend built me this amp as a pedal platform years ago and has since passed. I’m very interested in understanding the circuit and what it may be comparable to. Would anyone like to help me understand. Im obviously not an amp builder but have been reading up in an attempt to learn.

[Stevem]

Without looking long and deep under the hood the amp looks like it uses Reissue gold lion KT66 output tubes.

The Hammond 262F6 transformer is a added filament transformer to power the preamp tubes I am guessing.

The filaments for the 4 output tubes I guess are powered off of the main large silver transformer.
The power supply choke is mounted right next to that 262F6 .

That leaves the black transformer as the amps output transformer.

That’s all I have time to look at right now, I guess others will chime in for you with what the derive from looking over your pictures.

Please post up a rear of chassis shot.

[trobbins]

Output stage is simple PP quad pentode, with 1k screen resistors, (likely) 1k8 grid stoppers, grounded cathodes, common negative grid bias, long tail PI with feedback point and shunt output cap for hf roll-off.

You'd need a bias-rite or similar attachment to check quad balance, as there are no cathode resistors.

[Ten Over]

That leaves the black transformer as the amps output transformer.

No banana. P-TM0100 is the output transformer.

OT Marshall P-TM0100 Schematic copy.png

[Stevem]

Sorry !
I fell into assuming that the pt on it stood for power transformer.

[Ten Over]

Here is a preliminary schematic. I need pictures of the line-out tube wiring before I can even guess what's going on.

Surface to Air 100.png

[Ten Over]

I have attached numbers to the parts so that you can reference them when you tell me what the values are.

Surface to Air 100.png

[Matthews Guitars]

If the drawn schematic is right, then this circuit is similar to your standard Fender Bassman topology. Gain stage to gain stage to cathode follower to tone stack to phase inverter to push-pull output stage.

However the volume control is after the tone stack rather than being after the first preamp stage which is typical of the Bassman circuit. So it's a master volume without a preamp volume?

I don't know what amplifier type/category that falls into. It's not Trainwreck, it's not Fender or Marshall, and not Vox..

So what kind of amp has a post-cathode follower tone stack followed by the volume control pre-phase inverter?

I'm no expert, I'm here to watch and learn. Don't take my statements as gospel.