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Re: [Amps] 3CX3000A7 on 144 MHz

Subject: Re: [Amps] 3CX3000A7 on 144 MHz
From: Ron W4BIN Youvan <>
Date: Fri, 7 Feb 2020 15:45:54 -0500
List-post: <>
  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.
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