Re: Tube amp volume fluctuation?
This is why it's a good idea to always keep your old tubes handy, or have a bunch of spares lying around. Anytime something fishy happens, you can troubleshoot it with your other tubes.
First, change the power tubes. If it's still acting up, then change the pre tubes.
If it's still happening, clean all the jacks and turn all the knobs. After that, it's most likely a cold solder joint or a capacitor on it's last leg.