Mitchell Pro 50 low Buzzing

[Perkinsman]

An amp from a Riverside, Ca music store turned amp maker. I can’t find a schematic, the board used red, white & blue (& black) wires. This one is missing the reverb tank, two reverb wires stuffed into the amp. They They mounted a couple larger resistors right on the board & left burn marks.
My main concern is the low, annoying buzz that goes up & down with most of the tone controls. I’ve cleaned all controls, retouched the solders, replaced the e-caps, tested & raised the resistors off the board, changed out the cord but still have a buzz.
Is there a method to track down buzzing? What are the most likely suspects?

[J M Fahey]

You sure itīs not a hybrid?
I seem to recognize TO3 footprints in those large pads at the back.

Start from the beginning to simplify tracing.

Input jack must go to a 12AX7 grid, remember "in every amp there is a Fender", so short first tube grid to ground and then its output , after the coupling cap so you donīt have to deal with over 200V DC.
Any change?

EDIT: these guys say Mitchell was an ex Mesa Boogie employee and his amps are direct knockoffs.
The ones shown there certainly are, to the smallest detail, including polished wood cabinets and beige thick grill cloth visually similar to cane used by MB:
https://jedistar.com/mitchell-3/

Expensive to build (like Mesa ones) so I guess yours could be a simplified lower priced version: basic MK1 preamp (which itself is a "Fender with an extra tube for added gain" ) but in this case driving a 50W SS amplifier.

Not a bad choice and must still sound quite good, specially with a good speaker.

I would print a Mesa M1 (or Mk2) schematic and compare it side by side with what you have, ticking or correcting details with pencil.

Hum/buzz will be traced/troubleshooted like on any classic tube preamp.

EDIT 2: in case somebody still holds doubts, the "Mitchell Mk1":

[xtian]

I have a Mitchell Pro 100 on the bench now. It's all tube (SS recto). Had one years earlier, too. Good amps. OP's looks completely different--mine is components up. Is it going to be hard to flip the board over?

[The Dude]

FWIW: From what I've read, the Pro 50 is a solid state amp. The Pro 100 is a tube amp.

[Perkinsman]

It's the Pro50, it is solid state. There's not alot to this amp. Maybe 30lbs, 25lbs of it is the solid oak cab, at least I think it's solid. I think the buzzing is coming from inside the transformer, like the laminate plates are loose and a couple are rubbing. I've seen where someone used Deft and brushed it into the loose laminates and clamped it overnight. I might just want to replace the transformer. How do I know what size to get?