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The heaters are not run on DC, but on AC from winding XY.
The Z tap raises the heaters to the same DC voltage as the cathodes.
This high power resistor network (R47, R48, R49) provides the cathode bias without requiring a separate low voltage rectifier and transformer winding, but I haven't figured out why they draw current from both the 285 volt and 375 volt points to do that.
Edit: probably because a simpler arrangement would require an even higher wattage resistor somewhere?
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Old TV literature, New York World's Fair, and other miscellany
Last edited by old_tv_nut; 03-14-2021 at 08:23 PM.
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03-14-2021, 08:18 PM
Hybrid Mode
