It sounds like a preamp side issue as the amps set up properly but that's just a guess. But it could be in the amps somewhere. You can cross patch the preamp outputs to the opposite main amp inputs with RCA cables if there are separate jacks on the back. Some will disagree with me (and that seems to be sport for some people) but I'd suggest to recap the tone amp board after the power supply rebuild to see if that remedies the left channel issue. In general though if headphones sound fine and speakers don't that's sometimes due to open output transistor junctions. The DUB out jacks are before the tone control amp and except for the tuner and phono are pretty much coming from the aux or tape in jacks directly, via the function selector switch.
The front ends of that era did get rather cheesy and I've seen the shafts come out. I think this may be "normal" and while not ideal is okay. The drum wheel that the dial cord goes around will keep the shaft in place mechanically. It is unsettling, I agree! Kind of like those multi deck rotary switches that the flat shaft can back out on. I've adopted the standard procedure of fashioning a brass keeping tab and soldering it to the back so that can't happen. That great tip came in from my friend Tom/Catrafter. Anyway if the dial cord pulleys need to come off, say for a lamp housing repair or replacement, tape down the dial cord to all pulleys and tuner drum with masking tape (the good stuff, not blue painter's type) and tape the front end drum so it can't come off.
The front ends of that era did get rather cheesy and I've seen the shafts come out. I think this may be "normal" and while not ideal is okay. The drum wheel that the dial cord goes around will keep the shaft in place mechanically. It is unsettling, I agree! Kind of like those multi deck rotary switches that the flat shaft can back out on. I've adopted the standard procedure of fashioning a brass keeping tab and soldering it to the back so that can't happen. That great tip came in from my friend Tom/Catrafter. Anyway if the dial cord pulleys need to come off, say for a lamp housing repair or replacement, tape down the dial cord to all pulleys and tuner drum with masking tape (the good stuff, not blue painter's type) and tape the front end drum so it can't come off.


