[Amps] 3CX3000A7 on 144 MHz

[Ron W4BIN Youvan]

   Jim w8zr MU 4CX250B wrote:

>       Seems to me this problem may not be so troublesome. The dc
> resistance of the hot filament is 7.5V/51A=0.15 ohms.  If the B- return
> is on one side of the filament, and if we assume the plate current is
> 1ADC, then the maximum DC voltage drop across the filament would be
> only .15V

   There is none the less, a 7.5 Volts difference between the ends of 
the filament
and that (in a directly heated cathode) is a 7.5 Volt bias difference 
between ends.

>      Furthermore,  the filament emission is distributed across the
> entire length of the filament and not just at one end, so the average
> resistance is actually less than .15 ohm. What this means is that the
> variation in operating bias from one end of the filament to the other
> by using a switch mode power supply is at most a tiny fraction of a
> volt. For practical purposes, I think it could be neglected, which
> means a user would see no difference in performance, compared to
> using a center-tapped filament transformer.
-- 
   Ron  W4BIN - Understanding is much better than
                                     knowing how.