Tube Fire What Next?

I have a melody el34 integrated amp. I truthfully don’t know much about how to maintain it. About a year ago I had a well respected tech do some work on it and put in new tubes. Last night the family was listening to music and it looked like there was fire inside of one of the power tubes. Scared the crap out of my daughter. I turned off the power and unplugged it.  I assume I need to replace the tube. Is there anything else I should do? I have never biased the amp myself but I did just buy a multimeter which ironically just came this week. Can someone walk me through this so I don’t bust my amp or more tubes. Thanks for the help. 
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Showing 1 response by atmasphere

Actually the tube arced. This usually happens when the tube has aged out, or has been damaged. The usual culprit is a sort of paint on the cathode of the tube, which can flake off, and it is conductive. This is the genesis of the arcing.

I would replace the tube and see how the amp behaves. In some amps, the arcing can cause resistors in the amp to be damaged, in which case the amp might not work correctly when the tube is replaced (it won't bias up, the tube might turn cherry red or it might sound distorted). If you can set the bias that's good; play it and see how it sounds. If that's OK, the amp is OK and you just need to be sure that your tubes are biased correctly.

This can happen even if the tubes were biased correctly, since its a function of the condition of the cathode coating and not really anything else (although if over-biased can lead to failure).