The most dangerous of all are DC-coupled preamps and power amps. If the DC servo system in a preamp fails, the failure can propagate all the way to the loudspeaker. I saw this happen when I was visiting the home of a reviewer.
@lynn_olson The highlighted statement above is false.
I don’t contest what you saw.
We’ve been making preamps with a direct-coupled output (which we patented) and its been one of the most reliable design aspects of the preamps over the last 35 years. If it were to fail, our preamps wouldn’t make a high Voltage anyway, even as it warms up. As a result this is something that we’ve never seen.
If a tube amplifier was used, DC at the input would not have caused damage.
If a solid state amplifier was used, it should have gone into protect mode as any competent solid state amp will have a proper protection circuit!
So IMO if this anecdote is true, the designers of both the amp and preamp didn’t know what they were doing. Equipment should always be fail safe!!
Was the preamp of this story a tube preamp?