Hi, I have an AC-30 style amp. The other day (right before a gig) , the following problems began to occur: *Turn on and get volume at about 5% of what it should be (95% drop). What volume there is, sounds distorted. There's also a fairly loud hum once I take the amp off of standby. Oh, and there is some intermittent crackly pops (that last less than a second) andI believesignify the transition between working properly and not (though I haven't tested this enough to confirm it yet). After a minute or two, the amp would work properly and played fine for the first set. Left everything on during intermission so as to minimize a reoccurrence. Same problem when I pick up my guitar again for 2nd set: about two minutes of heart attack while everybody waits for me, and then it plays fine. Yesterday, I checked out the back of the amp and found two el84s to be redplating while the amp is malfunctioning. After a minute, I heard the crackle-pop, my volume comes back and the tubes cool down. There are 4 el84s, it's the two on the right side (as seen from the back) that are getting hot. Again, the problem is intermittent. My first thought is to switch the two power tubes on the right with the two on the left and see if the redplating follows the tubes or stays with the tube positions. I'm puzzled that two tubes are redplating, not one. The amp does have a 1/2 power switch, and I briefly tried diagnosing it in half-power, but the problem was too intermittent to draw conclusive results. Your thoughts and insights are greatly appreciated!