MusicMan 65, transistor driver

[JC@]

I guess this is going to be a long hunt. The amp works perfectly, but at a good volume setting when I hit hard a "low" note on the guitar there is a clean high pitched scratchy cold solder like sound coming out from the speaker. I'm testing it with the chassis on the bench and an external speaker.
Please help if possible

[Enzo]

Sounds like a parasitic. Apply a sine wave from a generator and advance the level - I use 100Hz a lot myself. Does the scratchy sound come and stay after a certain level is reached?

Scope the output. Is there a little fuzzy action on the peaks?

[JC@]

Sounds like a parasitic. Apply a sine wave from a generator and advance the level - I use 100Hz a lot myself. Does the scratchy sound come and stay after a certain level is reached?

Scope the output. Is there a little fuzzy action on the peaks?

Wow! Yes sir, it does.
The amp has been heavily modified for harp.
How should I chase down that parasitic?

[Enzo]

scope scope scope.

[JC@]

I get the point Enzo. So there's no magic button to press here then...
These MusicMans have quite a few HV picofarads range caps all around the power tubes and a couple more I've added, so that's not the cure in my case
Thank you

[Enzo]

It could be so many things, including interwinding arcs in the OT even.