Portacolor early model repair

[Electronic M]

Portacolor sets used series string heaters so if you pull any tube (except the HV rect which gets heater supply from the flyback and CRT which IIRC has its own heater transformer) there will be no load on any of the B+ supplies and none of the stages will draw B+.
You pretty much shouldn't pull any tubes from a series string heater set when variacing it, or if you do then at least monitor the highest B+ rail and stop the variac at the rails rated voltage to prevent damage to the lytics

There are 2-4 white ceramic tubular paper caps (IIRC Elmenco brand) that go bad and the lytics. Tin whiskers in the rear pots is definitely a common PITA.