Tube Fire What Next?

You may have been running the amp too hot. Ensure biasing does not cause the tube plates to glow red. Check in the dark.

Thanks everyone. Millercarbon my melody has the same set-up so thanks for pointing that out. Just to be crystal clear when I bias the amp the amp should be plugged in and turned on, correct?
Noromance, thanks for that comment. in the future I will check. 

Pull the old, check the pins, tighten if needed, install the new, (give them a good visual).

It's never a bad idea to back the bias off a bit (Counter Clock Wise), FIRST. Then TURN the machine ON, and warm it up, 10-15 min.

LOOK!! Make sure your new valve are not red plating for the first 10 minute or so.. pay attention.. Now do what millercarbon said. Set your DMM (digital multi meter) or an analog.. I don't use analog meters,  EVER.. Set to mA.

Turn the volume DOWN all the way.. ok. They say it doesn't matter, it may.. or may not. To be on the safe side.. Turn the volume down...

Be sounding like heaven in no time..

Recheck in 24 hours.. Keep it tuned up..

Regards

Yes. Plugged in, turned on, and warmed up. 

For now while its missing a tube I would leave it unplugged. Unlike SS amps that don't care tube amps don't like to be on without being connected to a speaker. Its overkill, but just to be safe I turn off and unplug when changing tubes or speaker cables.  

When its warmed up half an hour or so the black neg lead goes in the center and the red goes to one side or the other. You want a really small screwdriver like for glasses. Do it right and the probes will hang in there leaving a hand free to turn the screw. That's my preferred technique as otherwise you're trying to hold two probes with one hand while twidding the screwdriver with the other which is a dexterity test I have passed but would rather cheat my way out of, if you get my drift.

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).