FireFly Tube Amp Oscillation

[noah_swanson]

So I built a firefly tube amp. I modified it a little by adding a tone stack and a 6CA4 rectifier.

It sounded great for the first week. Now it will randomly "shift" tones and sound like a wah pedal all the way forward.

Also, if I put the volume knob past "8" on the "boost channel," it starts oscillating.

I tried bypassing the tone stack and neither of the problems were resolved.

I've attached my schematic as well as the original. Any help is appreciated!

[txstrat]

This all might be a problem of lead dress inside the chassis.
I'd take a chopstick and try moving the cables around to see if that recreates the "funny" sounds and/or the oscillating.
The oscillating might be damped/stopped by using shielded grid wires in the first stages.