DC on an amps input- how bad is it?

[MikeH]

I recently spent several days debugging a design because of bad switch popping.  All the while playing it through my amp.  I'm pretty sure I even left it plugged in with power running through it overnight.  Anyway, the switch popping was because a short was bypassing the output cap, and was sending about 2 volts of DC right to the output.  Anyway, just curious; how bad is that for my amp?  It's a fender super reverb, so no cap on the input to block the DC.  Obviously the amp seems fine, but does it decrease tube life or something?

[R.G.]

On a Fender SR, it's probably fine. If there is an effect, it is on the first preamp tube.

Tube amps are AC coupled inside, so the DC may have affected the first tube stage bias, but there is a cap blocking the DC at the plate of the first stage, so an damage, even theoretical, stops there.

Some hifi setups are DC coupled throughout, as the ... um, hifi fancier-tweakos ... have this idea that your ears can hear lack of DC response as degraded audio. Interesting theory if you can keep from laughing. Anyway, if you happened to use one of these setups, the DC would be amplified all the way through and would likely have caused a speaker to burn out if it was a lunatic-fringe owner who had removed the protection mechanisms to let the audio be more pure somehow, or would have tripped the DC output detector which many of these have incorporated to protect from just such a problem.