The outputs are not in a friendly location, Can I install a resistor on each rail that feed the collectors of the outputs?
As long as the resistors are between the power rail and the collectors, and not between (say) the power supply and the amplifier board itself.
I was thinking, which is dangerous, but this unit draws 450watts at full power. I can run the volume up all the way with no signal with no problems in 2 channel mode. I can also run volume up very high in 4 channel mode with a FM signal. I am using a 100 to a 200 watt bulb. The volume will get higher with the 200 watt bulb with no problems. I also have a variac if needed.
I would recommend no testing with any input right now.
I would want to see you being able to wind the volume all the way up, and down, and at any speed, with nothing much happening.
Just to minimise the risk of picking up noise, I would short the inputs to ground.
I did find a 1000MFD 35V cap that tested at 922mfd. It was attached to the power supply feeding the 400hz oscillator and Dolby processing boards.
That's within spec for an electrolytic capacitor. If you have any reason to be suspicious about it, you could replace it, but I suspect it won't really make any difference to the problem you're having.
Do you think it would be smart to try unit off of the dim bulb at this point?
With the resistors in series with the output transistors, and with caution, and with a hand close to the power switch, yeah.