i finally got it back from the repairman! and it sounds wonderful.
the choke had melted before, which he fixed, then it melted again. i brought it back to him a second time and he said that the
vibrations from the cabinet caused current to jump between the power tubes, overloading the choke (which then filled my
basement with a nice thick cloud of smoke).
he also said that 6L6 tubes in it were nearly dead. which is funny because i bought them brand new from
my local music store, leading me to believe that i got sold some bunk tubes.
this is day 2 and it is still functioning. things are looking pretty good.
Looking at a diagram of that amp... it could be that some dodgy/vibrating connections at/around the tube sockets (like Will says) were interrupting the bias voltage that normally keeps the power tubes in their safe range. Cut off that voltage, and the tubes would pass way too much current, part of which would overheat/damage the tube plates, and part of which would stream through the tube screens and then heat up the choke.
So it could be that the tubes were of OK quality originally, but were suffering along with the choke. Hopefully nothing else got damaged?
