OK, got the bias set and let it idle for about an hour. Nice and stable without the oscillation, and idles pretty much cold wheras prior the sinks used to get moderately warm. Replaced the LF356's with LF351 and rechecked - bias dead on, and offset about .7 mv on both channels. Put it on my trusty 225 watt test resistor, and got good signal (and heated that bugger up quickly!)
All that remains for now is to replace the PL36 dropping resistors . . . (waiting on the parts . . . didn't have those in 5w).
All is good now, so very close to done, and my "long term" factory comp 400S2 that I have had since about 1984 will have a slightly goofier older brother
(Swapped the faceplates as well, since I had drilled mine pretty ugly way back when to rack it . . . ).
So, all told: Recap PL36, update main caps, update op-amps and pwer resistors (as per SB), added precautionary diode pairs for lockup insurance, and added Don's DC protect board, added 4x caps to stop oscillation. Should be good for another couple of decades . . .
All that remains for now is to replace the PL36 dropping resistors . . . (waiting on the parts . . . didn't have those in 5w).
All is good now, so very close to done, and my "long term" factory comp 400S2 that I have had since about 1984 will have a slightly goofier older brother
(Swapped the faceplates as well, since I had drilled mine pretty ugly way back when to rack it . . . ).So, all told: Recap PL36, update main caps, update op-amps and pwer resistors (as per SB), added precautionary diode pairs for lockup insurance, and added Don's DC protect board, added 4x caps to stop oscillation. Should be good for another couple of decades . . .