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From pwz@cw-f1.umd.umich.edu Tue Oct 13 12:21:47 1998Date: Tue, 13 Oct 1998 12:21:43 -0400 (EDT)
From: Paul Zitzewitz <pwz@cw-f1.umd.umich.edu>
X-Sender: pwz@bael.umd.umich.edu
To: Clarence Bennett <bennett@OAKLAND.EDU>
Subject: Re: B battery
MIME-Version: 1.0
Clarence,
I'm off campus and can't reply to the list serve, but here is the answer
to the C battery problem.
In the real early days, before indirectly-heated cathodes, the filament
reference voltage was fixed. It is necessary to bias the grid negative
with respect to the filament. Small batteries were used because there
was no current drain. I actually saw such batteries on a battery-powered
portable radio my grandmother had.
When the indirectly-heated cathode was developed, the cathode could be
biased independently of the filament, now called the heater. The cathode
resistor was then used so that the cathode current could establish a
potential difference between the cathode and ground. Then the grid could
be left at the ground potential.
Paul (ex K9EXL from the 50s)