Hi bass,
first of all it’s a BF bandmaster head, with 6L6 tubes.
the power tubes are quite new (well, nearly a year old now) but maybe they just been through some hard beating due to a resistor being nearly dead (don’t know the exact name, it was a 470ohm resistor crossing one valve base, I replaced it a month ago). the filter caps were replaced three months ago, it should not be that but who knows? anyway after the capacitor replacement a lot of hum and noises disappeared, so the new ones seemed to work. could it be dead tone circuit condensers?

I looked for some info on the internet, next week I’ll try to check if any of the preamp tubes does not light up or something like that.
when I last played the amp two days ago there did not seem to be any sparkling anywhere but I do not know it there was anything going on in the inside of it.
it might even be a dead solder joint, after all this is a 42 years old amp.
anyway next week I’ll check if the joints are ok, and leave the results here.
thanks for now! have a nice weekend.