You know, I was just thinking this morning... I forgot about those 50K resistors on the plates of the 12AX7. A measurement of around 9VDC on those sounds about right. I never actually measured mine. :oops:
Mine are all 47k's - I've never even seen any 50k resistors !!
I just tried some decoupling caps to ground from the op amp pins 4 & 7
( TL071 remember ) and also from the trimpot + & - to ground, plus a
10uf from "bias" to - on trim pot.
I got a slightly "smoother" sounding OD, but still have a serious "level"
drop on full gain.
At clean gain pot setting, I have a volume lift above unity and no more
"farty" stuff going on.
If I used an output boost on this, it would be sounding fine, though at
full gain, its still only a "mild overdrive" tone .... ??
BTW - it's not re-built yet and is starting to look like "Frankensteins baby"