It's the second time I have this problem with my SF Deluxe Reverb, as soon as I turn on in play mode I hear this 60 Hz hum in the speaker, and no sound. There is also a tiny bit of smoke and a hint of that lovely burnt smell. The last time it happened I noticed the two 100ohm resistors going to ground from the pilot light 6.3v heater wires looked burnt (I had already changed them before). I saw nothing wrong inside the amp, tried another 5U4GB rectifier and everything seemed back in order for a few days. Then today the same thing happened again at practice. I noticed that those 2 100ohm resistors are absent on the AB763 schematic and appear on the AB868 and later schematics & layouts. My other Deluxe Reverb (from 1979) seems totally fine, the original 100ohm resistors look and test good. I also have a 77 Princeton Reverb on which I had to replace those same two 100ohm resistors, they were so burnt, they were severed in half. Maybe I'm chasing the wrong thing here, any idea? Are those resistors necessary for the SF amps, and not for the BF ones? Slightly different PT? Nothing got damaged yet, but I would like to know what the recuring issue is, and if anybody experienced the same problem.