[AMRadio] Class C modulation

[W7QHO at aol.com]

In a message dated 3/20/02 11:12:38 AM, brett.gazdzinski at wcom.com writes:

>I think the best way to modulate these tubes is with the separate
>mod transformer winding.
>You can do fine with the choke in the screen circuit, but
>the peak power seemed to be lower than with other tubes.

The military T-368 feeds the 4-400 PA screen through a dropping resistor from 
the 2500 volt (non-modulated) supply.  No screen choke, the 80K resistor 
provides sufficient impedance for the screen to self modulate.  Seems to work 
FB.  I have tried tying the hot end of the screen resistor to the modulated 
B+ feeding the plate circuit but this made no apparent difference in 
modulation characteristics, either as viewed on  the scope or during 
on-the-air tests.  BTW, the book says additional grid drive will be required 
with self modulating screen circuits.

Dennis D.  W7QHO
Glendale, CA