Hi wry and watchful,

I'll take a stab at this; I'm a technician.

Even after unplugging an amp, there can be high voltages present that can shock the crap out of you. Power supply capacitors, if you know what that means. Though I know how to eliminate these dangers, it would be irresponsible of me to try to describe this for you.

These are the tubes: 12AX7, 12AT7 and two 6L6. The 12AX7 and 12AT7 are smaller pre-amp tubes, the 6L6s are physically bigger final output tubes. You could probably remove the tubes(AMP UNPLUGGED, AND YES, I AM SCREAMING HERE) and have them checked if you know someone with a tube tester or a similar amp which uses the same tubes. You want to avoid getting the oil from your hand on the glass of the vacuum tubes; use a clean rag when removing the tubes. After an amp has been on, they can be quite hot also.

Having said that, I think it is more likely something else burned up other than a tube, but one never knows, do one? If you were in northwest GA, I'd take a look at it for you. Then I'd probably point my finger at it, and laugh out loud. Good luck,