What happens when a tube amp fails?

What happens when a tube amp fails....the repair tech rings his hands in glee.

I've had a peaceful coexistence with tubes for over 10 yrs now. There have been a couple of instances but a fuse was all that "went". Cause in both cases was a short in the rectifier.

I have a tube tester and that helped identify the shorts immediately. I do test tubes with it but I think the best test is to have a backup set and put them in once a year to "test" against the aging ones.

I have seen, and heard, various modes of failure, but, amazingly, not at all in my own gear. All I've had to do was replace tubes that have started to go weak (sound becomes dull and muddy).

The most interesting was an amp at a dealership. I went there with the intention of buying the amp after a couple of auditions. The dealer offered to turn it on for one more listening. Something in the amp instantaneously vaporized (probably a resistor) and what I saw as a tiny mushroom cloud rising from the amp.

On another amp at a dealer, a bad tube socket would cause a loud pop through the speakers once in a great while; that pop was spectacular and quite unnerving to me. A friend borrowed the amp from the dealer not knowing about the condition and put them on his 105 db/watt efficient speaker. He said the "pop" rattled the windows and shook the whole room.

If you really want a big surprise, try accidentally wiring into a circuit a polar capacitor in the wrong direction--big bang and capacitor bits everywhere.

Wow!, I have owned tube equipment,always went on to the next componet before failures, never went thru these scenerios!, thinking of buying a tube digital source that I once owned before, that sounded magical to me, looking at all that has been said here about tube failures has me having second thoughts, solid state now seems ever more appealing.

Sheesh. The tube amps have the tubes in sockets for a reason. The reason is they are user-replaceable, like a light bulb.

The usual remedy is to install a new tube when one fails. Its not rocket science.

Some power tubes will require some adjustment of the amp, the procedure should be in the owner's manual. Some amps have auto bias and little if any adjustment is required.

It is true that many power tubes fail due to arcing as the cathode structure degrades and starts falling apart. The prudent manufacturer will build the amplifier to withstand this sort of behavior, but oddly enough we do continue to hear about amps that smoke when a tube fails! That says more to me about who built the amp than it does anything about the tubes... We've been seeing tubes arc for as long as there have been tubes, this sort of thing should be sorted out. I avoid amps that have this sort of design problem.

An example of a tube amp that holds together with tubes arcing is the Dynaco ST-70. Now if Dynaco could make that happen way back in the late 1950s you'd think it would be a walk in the park for a manufacturer from the 21st century :)