Oh the joys of tube power amps... Seriously,before you do anything, I would check the voltage at the outlet you are using.
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Demonic possession is often NOT covered under warranty (or divorce decrees seemingly)...I think tube amps should last for about 72 years with only minor maintenance and tubes should die a long protracted death, not flame out. Wall voltage is rarely the issue but possible of course, so maybe it's speaker impedance matching, a crappy amp channel needing caps or resistors or something, or your horrible karma from another life spent as a bad, bad person.
I invested in a Variac just for this type of problem. If you bring up the line voltage slowly, you have a chance to measure the voltages on the tubes, assuming you have the schematics and a digital voltmeter. If no schematic, then compare the voltages of the working side with the one not working.
I also have a tube tester to check all the tubes before powering on the amp. Tube testers are relatively cheap and if you have tube equipment, well worth the investment. Make sure you get one that measures transconductance not just good-bad indicator. I use the tube tester to make my own matched set of output tubes rather than pay a high premium for them.
Plates glowing cherry red indicates there's a huge current draw of that tube only. This could be caused by a defective coupling capacitor which allows plate voltage from previous pre-amp stage to be on the grid of the power amp tube, thus forcing it to conduct max current.
The loud hum also indicates the most common problem: bad electrolytic caps in the power supply. I also invested in a ESR (effective series resistance) capacitor tester. This will measure caps "in circuit" if the cap is bad (leaking, shorted, etc.) and gives you the actual value. Unfortunately it gives false reading if a filter cap is attached to a choke or power transformer, so I have to clip one lead before I measure it.