Success

[redshark]

At some point I had something similar, not identical. Playing a f# note was giving me a rattle, so I though that it was the obvious microphonic tube. At same time I was moving wires in the volume and tone controls and that wire that goes from the 500pf cap in the board to the treble control I was adjusting the distance in relation to the volume pot of that one to try to minimize noise and after moving all those wires I noticed that I could never get that "microphonic like" rattle when I play a f# note again. Very strange. Also moving those wires in diferent combinations gave me the "feel" of more or less gain and more or less high end...who knows, I ended up most of those things that were inducing some feedback in the preamp stages by using a second shielded wire from V1a (pin2) to the volume pot. That second shielded wire helped the transition from long sustain to the harmonic feedback (bloom) and made the amp sound less congested.
Still I would check for cold solder joints, doing some chopsticking could expose some joints that maybe look good on the outside but are not as solid as they seem.

[Big Jim]

Gotcha Redshark,
I am on a brief trip. When I get back the 1st of the week, I will get back on it. I will probably change the preamp tubes first, again just to rule them out. I have an extra piece of shielded wire to go to the volume pot, so that will follow next. And while I'm at it I will continue to search for another cold joint, and chopstick the thing etc. Got it. By the way, would it be a good idea to ground the shielding to the bus wire or something at the pot side? Thanks for the help, Redshark. Jim

[PlinytheWelder]

I took a lot of ideas from Allyn's 80w build for mine. Check the layout here:
[img1250]http://verosurfcam.com/80W.jpg[/img]

Note the 2 shielded cables on V1...

[Big Jim]

Thnanks for the info...I'll shield that wire to the Volume pot and see what comes of it!
Jim