Crown DC300A

The DC-300 and 300A were the ultimate in technology back in the 70s. They are still sought after as they are reliable but can die if overloaded for too long.
Because they work down to DC, if your pre amp has a fault a pushes a volt or so of DC out, the DC-300 will amplify it, (as it is designed to do), fry the speakers and the resulting short circuit load will overload the amplifier.
In my experience of over 40 years of sound engineering with these and newer Crown amps have never had a problem but then, I am looking after the PA.
Transistors do not degrade and the semiconductors in the DC range are good for up to 75 Centigrade, at that point the amplifier will feel like a room heater and shut down.
Back in the 50s and 60s, germanium transistors were the latest semiconductor, (Westinghouse produced XB113 type) and they had a gain around 5 – 10 if you were lucky. They have a shelf life of 25 – 30 years, silicon is not the same.