Yep Joe beat me to it, lol. I'll post it anyway.
If the power transistors are already blown (open circuit) ,, then no current can flow and bulb will only glow while the transformer and stuff charges. then it will barely glow, indicating little current is flowing.
The idea is that if the circuit is dodgy and goes unstable then the *current limiting light bulb* will dump a lot of current which instantly drops the voltage stopping it blowing up expensive parts.
Over current is what kills the Actives.
Bare in mind these are nearly always Direct coupled units and if one thing goes it often takes down other actives faster than you can swipe your credit card.
Just go make a light bulb unit,, they save lotsa money and tears.
I should know as I built many discrete test power amps and I lost count of the amount of actives I blew up just trying to work out How they function.
If you have big voltage on the speaker output (this is the hum) you have deeper problems.
If it's the classic LTP (Long Tailed Pair) front end then it might help if you can understand that the bases of those first two transistors are key to the design. They have to be kept at close to Zero VDC.
The FB resistor helps stabilize this and keeps the Speaker out close to Zero as well.
Though some DC offset is usually present,, maybe ~100mV.
Though I've measured some old working Amps with half a volt on the output.
Some designs are obviously more robust than others.
Yes you will have a hard time finding schematics for Torque stuff.
I did repair a Torque Fold back a while ago might see if I can dig up the paper work.
I drew up the power stage and found it was no big deal and replaced the obscure labeled output devices with good old 2N3055 and it's now fine.
yours might be different design.