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RE: Why is Square / Rectangular Wave Deal of the Day?

Posted by Triode_Kingdom (A) on December 8, 2016 at 09:32:24

In Reply to: RE: Why is Square / Rectangular Wave Deal of the Day? posted by dave slagle on December 8, 2016 at 07:38:03:

"Suddenly the tube will draw in the realm of 13ma of current and if we switch to 7.5Vac the bias reference goes to the midpoint of the filament and we get 8ma."

Maybe we have a miscommunication, but I think you're not grasping the concept of a floating, differential heater supply. The only ground reference is the tap on the hum pot. If that's electrically centered, bias voltage and current are unaffected by the AC heater supply, even when analyzed for instantaneous changes. Put this into SPICE, insert a 0.1 ohm resistor in series with the hum pot wiper connection, and you'll see no HF current flowing to ground. Yes, there's a constantly changing gradient across the filament. However, it's balanced with respect to ground, always sums to zero, and has no effect relative to bias voltage or the common mode signal path.

Edits: 12/08/16

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