I tried everything I could think of but nothing effected the oscillation in any way whatsoever------ lead dress, shielded cables, grid stoppers, snubber caps, etc. I had to put the amp away and work on other amps several times due to the frustration of getting nowhere with troubleshooting this one.
I had swapped countless preamp tubes but had always used the same true NOS matched pair of RFT EL34's------ tonight I installed/biased a pair of the Chinese GG (Guigong) EL34 "Super Tubes" that CE sells (I had put the other pair of a matched quad in a hi gain 50 watt prototype earlier in the night and this pair of EL34's was on my bench)
OSCILLATION GONE !!!!!!-----
- - - 
I re-installed the RFT's and the oscillation returned----- the RFT's tested matched and strong in my new Orange Valve Tester but were a problem in the amp at high volume levels.
I put in a good matched pair of used Mullard XF4's---- no oscillation
A lightly used matched pair of St Petersburg Svetlanas----------- no oscillation
Now I have to remove the circuit changes/tweaks that I installed to try and eliminate the oscillation in the preamp (which was never the problem--it was that pair of RFT output tubes)---- snubbers, etc---- then I can see how the circuit is going to sound in stock/near stock spec.
Then I can re-install the Lar/Mar PPIMV that I initially built the amp with and later removed as part of the troubleshooting process.
This build has been a thorn in my side for a few years now---- I'm a happy amp builder now that i'm on the way to getting it 100% operational and tweaked to my ear.
It looks like this:
http://s46.photobucket.com/user/gldtp99 ... t=3&page=1
http://s46.photobucket.com/user/gldtp99 ... t=3&page=1
Gut shots?
