Filament balance pot

[Rick Erickson]

[So, my hunch is that Lowell's Twin has those two 100-ohm resistors mounted on the pilot light. He'd have to take them out if he wants to use a hum balance pot,]

No he wouldnt. The hum pot will still work fine even with the resistors in place. They would be redundant though and therefore not necessary, but they wouldn't cause the pot to burn. My guess is, assuming the power tubes are good and that there is no green/yellow stripe wire to chassis, that the heater winding center tap is internally grounded to the transformer core. Seems like I just discussed this on another thread...
The orange wire is connected to an internal copper shield for noise suppression.

RE

[lowell]

Ok thanks everyone.... alot of things have become more clear to me through your posts regarding heater taps and center taps. I did not know that the center tap could be internally grounded... that MUST be it, cause there are not any 100ohm resistors to ground, and not on the pilot either. RE and RM thanks for the info on the power transormer orange wire typically being a ground for the PT - good to know. I will look for the green/yellow wire, if it's nowhere to be found then it must be an internal ground. Shea and others - I had the pot outer leads to pins 4/5 and 9 on the preamp tubes and the center lug of pot to ground. Anywho I understand this whole heater layout thing a bit better now, thanks everyone.

[Enzo]

As they said, measure voltage at each heater pin on a socket to ground. If you get 3v at each, ther is a grounded ceter tap. or with power off, is there continuity to ground from the heater pins of a socket? If so the heater is grounded, most likely at center.