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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.
Last edited by old_coot88; 04-14-2020 at 12:25 AM.
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