JCM 2000 100W Blown power tube

[hyperk]

Hi

This is my first tube amp and I'm kind of a noob, so I'm wondering if anyone can chime in and give me some info about what happened.

A power tube stopped working today while I was playing. The amp suddenly went quiet and I noticed one of the power tubes was dark and it seemed to be hotter than the other 3 tubes.
The tubes are old and have been used a lot. I also didn't allow the amp to worm up properly, I began playing less than a minute after turning it on.

My questions are:
1- Did the tube failed because of wear and tear, or is it possible that there's some problem with the heating circuit and it was getting too hot?
2- Do I need to replace all of the 4 power tubes?

[martin manning]

This is my first tube amp and I'm kind of a noob, so I'm wondering if anyone can chime in and give me some info about what happened.

It's not easy to diagnose failures sight-unseen from a limited description.

A power tube stopped working today while I was playing. The amp suddenly went quiet and I noticed one of the power tubes was dark and it seemed to be hotter than the other 3 tubes.
The tubes are old and have been used a lot. I also didn't allow the amp to worm up properly, I began playing less than a minute after turning it on.
My questions are:
1- Did the tube failed because of wear and tear, or is it possible that there's some problem with the heating circuit and it was getting too hot?

So at this point it has one dark tube and doesn't make any sound? The schematic I'm looking at shows individually fused filaments, so it's likely that a blown fuse is the reason that one tube is dark. If there is no sound, the high voltage fuse is probably open too, and my guess would be that the dead tube shorted internally and took out the fuses.

2- Do I need to replace all of the 4 power tubes?

I would start by checking all of the fuses to see if there are any more potential problems. If the shorted tube hypothesis still holds up, pull all of the power tubes, replace the fuses and check voltages. If everything looks good, replace all four tubes with a matched set.

[xtian]

I also didn't allow the amp to worm up properly, I began playing less than a minute after turning it on.

There is no reason to let your amp warm up before playing. You can't hurt it this way.

[hyperk]

Thanks for helping.

Upon inspection I found that the high voltage fuse is blown, all the 4 internal fuses are ok, and the failed tube appears to have lost the mercury layer on its top, it looks like it evaporated.

[martin manning]

Upon inspection I found that the high voltage fuse is blown, all the 4 internal fuses are ok, and the failed tube appears to have lost the mercury layer on its top, it looks like it evaporated.

That material is not Mercury, it's mostly Barium. I'd replace the HV fuse, install a new set of tubes, and reset the bias.