[AMPS] Filament supply?

[Tom Rauch]

> Why is there no AC hum on the transmitted signal?


Thermal lag and balance. 

The filament (and cathode) does not have time to change 
temperature. Emission level is constant.

A directly heated filament can be balanced so the ac component 
caused by voltage drop across the filament is almost totally nulled 
so far as the cathode's emission current is concerned. That's why 
we normally use center tapped transformers in directly heated 
tubes. 
73, Tom W8JI
W8JI@contesting.com 

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