[Radio Wrangler]

Multiple revisions of a power amp is a sign that the manufacturer had problems with it.

Looking at the schematic there seem to be a few gotchas. Things that bitten designers have learned to avoid.

Switched speakers and no catching diodes across the power devices to keep the output voltage within the rails.

Darlingtons without resistive pull-downs on the first emitter

no capacitor across that series pair of bias diodes

Nothing to protect the darlingtons from reverse b-e voltage on transients.

I'd EXPECT these to keep blowing up

0.5A seems an awful lot. As Alan says, the bias should be rather low. Notice the darlington bases are separated by two 1N4148 drops, yet the darlingtons will need four Vbe drops to start turning them on, so there really isn't any bias voltage at all left to appear across those emitter resistors. By rights it should be showing poor crossover distortion.

So, you still have a deeper fault left in this amp.

From that schematic I would not consider such a unit to be a 'keeper'. I'd have doubts about whether it was worth fixing to be honest.

David