Hi Folks,
Happy New Year , I finished my AA wreck build a few months back, It turned out great, played around with it and have got it where I like it .
I ended up putting the grid resistors directly on the sockets and not on the board ,
I played around with output tubes, tried 6V6's , KT66's and ended up with EL34's ,
Also added the Fischer PPIMV #3 that phase cancels the signal from the grids to of the EL34's , it works OK to a point , from full to about 1/2 is useable , after that it just loses its mojo. I actually keep it on full now .
I squeezed it into a combo cabinet slightly bigger than a 5E3 cab, it's so compact that people don't realise the beast inside 😂 and played around with speakers, I ended up with the Eminence Wizard which is great with the circuit , it's a very efficient (103db) 75w take on the Celestion G12H30 , it can handle the EL34's with ease.
I did have some issues with the biasing , I tried everything from 50 to 70% plate dissipation , there was serious harsh grainy squawks on certain notes when biased too cold ,I discovered the circuit is best suited to 70% plate dissipation , that's the Wreck spot , anything lower just doesn't seem to cut it .
After a few months of testing and playing in gigging situations , I think I'm pretty happy with the results.
I used a combination of Jupiter and Sozo coupling caps, basically what I had in my stash , they're still burning in so it'll only get better with age ....
It's a little compact combo , a wolf in sheeps clothing .... very happy with the results ... next up a Rocket and a Liverpool
here's some pictures
regards
Mark
Commenting on your harsh distortion...
Since you've ruled out most of the possibilities, you might be right about oscillation. PO is pretty difficult to diagnose without a scope. If you have a scope, watch the AC as it goes through the amp. Watch each stage with no input, but volume and tones up, and look for high frequency wave forms coming out. They're usually pretty ugly, like static.
I hope that helps
Bob