Help. High freq noise

[Danplifier]

I'm betting on a parasitic oscillation. The fact the the pitch increases with the brightness setting up into the ultrasonic is the reason. I've NEVER seen a microphonic tube do this.

Is this amp the ordinary Special 6 or the gainier model??? I'm looking up info for it. The first thing I notice in the open chassis shot is that the input lead is too long and the OT is on the input side of the amp.

EDIT: Still looking at the chassis shots... The OT secondary leads are WAYYY too long and run right under the preamp board and input!!! The input lead is stuffed under the board on top of the OT!!! The output jacks are located center chassis under the tone control!!! I would be much more surprised if the amp DIDN'T oscillate. Someone with experience could stabilize it, maybe. But it'll take some tweaking and a long effort. Relocating leads, possibly grounds, maybe adding a bleeder cap. Trying to idealize that layout isn't for a novice.

Oh no. That doesn't sound too good.

It's just the ordinary special 6 - head version.

I'll just have to leave the volume at 12:00. Should be loud enough on stage with it mic'd up.
Either that or have the tone set at 12:00, so then I can have the volume at 1:00 to 3:00, and just buy an EQ pedal.

I've already ordered new tubes now so I'll see if they make any difference. I should get better tone even if it doesn't fix this problem so not to worry. I will report back in a few days.

Not a bad amp for £100 anyways