Hello..my first TV

[Donj]

jr,
Tube is a 12at7. Split filament maybe?

[jr_tech]

Originally Posted by Donj

jr,
Tube is a 12at7. Split filament maybe?

Yes, so indeed, the heater for 1/2 of the tube runs on AC and the heater for the other 1/2 runs on DC.... I don’t believe I have seen that before. Curious!

jr

[old_coot88]

Yes, the whole 12AT7, 'AU7, 'AX7 family have split heaters with pin 9 as common. So they can be run in series on 12V, or in parallel on 6V. But V2 in your set evidently has 6V DC on one and 6V AC on the other.

(Edit) jr_tech nailed it first. I never seen that arrangement before either. Just a SWAG, but since V2a is the tuner's oscillator, the DC heater scheme is to minimize 25 cycle "FM-ing" of the oscillator.