Morning Mike
Setting bias...
AMP HAS TO BE UP TO TEMP .. The small signal transistor as it heats or cools will affect this setting, so if you set it with the amp cool.. it will drift.
These amps drift a fair amount anyway.... ~ 10 mv or so... so worry about 40 mv drift, not a 10.
How clean the connectors can affect this is a BIG WAY
ALSO DID YOU SWAP THE DIODE (VD -1212) near TR-05 ?
BTW you have Ham gear... I assume you are not using it while working on this?
The RF rejection of these amps is not so great
Do you have a laser thermometer ?
R-18 & 22 in the constant current bias section are 120 ohm fuse resistors.. have those been replaced?
Might be a good watchdog move to monitor the regulated +/- 65 volt rails while running ( maybe a bit OCD ) but it might be a " tell".
Sounds good......Can I get a close shot of the #1 2507 board.....? When this round is done ?
One of my concerns is both your original amps went poof,
I assume we are using the 4 2507's that came out of the 2 old amps first AND you are taking the time to change out the E bay boards to New resistors & other components....
Wouldn't it be BETTER to change out all the passive components on the board we are testing now....?
Seems like a duplication of effort AND testing with older stuff that was put under stress.
The reg board doesn't have to do as much work as the driver, so it wasn't as critical ( in my mind ) .
I would suggest if this 2507 works ( for the most part ) is to do the wholesale change out of "R's" (test) then "C" values.
In addition do you have plenty of heat sink goo on the 2507 TR-10/11 and it's TIGHT ?
Side note if you do screw down the 2507 to chassis it will give you a LITTLE more heat sink... but not as much as you would think.. heat rises..
Ok great so what's the NEW PLAN?? ( Clean stable 1 channel at the end of 34 ) BAM !