Bias Tests
Tonight I checked out the bias circuits. Some of these points are difficult to get a mini grabber on, but I managed to find another component that was connected, and clipped to that lead. After recent setbacks I am careful to shut the DBT off before repositioning the mini grabbers.
First I tested per John's description and put a DMM between TR15/B & gnd, and between TR17/B & gnd. I turned VR03 2 turns CW and took readings, turned it 2 more turns CW and took readings, then turned it 4 turns CCW to get it ~ back to where it started. The results are shown in the attached graphic, including readings from the 'good' right channel.
The lower rows show the relative difference of the readings in mv, so I can conclude that my circuitry is working as John described.
Then I moved to the emitters of TR 15 &17 and they followed the same pattern when I adjusted VR03, as did readings taken at the base leads of the OP TRs.
B+ and B- going to the collectors of the OP TRs is a solid ±52vdc.
The emitter leads of the output TRs do not change when VR03 is adjusted. They both drift around, and read between -12 & -14mv, as does the junction of the two emitter resistors. Voltage readings across the emitter resistors ("Bias Voltage") is solid at 0.00mv.
Looks like I need to remove the OP TRs and the emitter resistors and check them out of circuit.