A Bassman 100 on the bench.
Missing PT (burnt, I suppose …)
OK, once the new PT is in place (a Hammond 290FEX) and the four 6L6GC changed, time to rebias this thing. On this model, there is a balance bias pot and not a “real” pot to set the bias. Balance bias is easy : the minimum hum, the better !
Unfortunately, this does not allow to set the current bias, and on this Bassman, the current was as low as 18mA (for 440V to the plate). So I replace the 15k resistor by a 1k “security” resistor and a variable resistor (a 50k I had, but a 20k should be even better) :
I replaced the 40 years old Mallory caps (I keep them, maybe someday I will try to reform them ?)
I noticed a wire going … nowhere ! Soldered at one end, cut at the other end ! A previous mod ? A “factory” mistake ? Anyway, I removed it (and the amp works well after having serviced it)
New caps …
Another small issue : a very nice blue light in a 7025 tube :
Anyway, the baby can sing again !