According to clarence at snyder dot on dot ca:
On 24 Sep 2007 01:10:00 GMT, (DoN. Nichols)
wrote:


I suspect that portable radios in the past (tube days) used F
cells more commonly than today, which is why the 6V lantern battery was
designed to be just the right size to hold four F cells.

The "F" designation was for "F"ilament use. Lots of old batteries had
1.5 volt filaments in the rectifier tubes, so you had an "A", a "B"
and an "F" battery.

But the "F" here indicates the *physical* dimensions of the
cell, not its function in the circuit, just as the 'D', 'C', 'AA' and
'AAA' cells which are still common designate a physical size. I'm
trying to remember the designator for the *big* single cells with a pair
of knurled nuts on the top for connection (or sometimes a Fhanestock
clip for each terminal). Those may have been 'G'. I know that as a kid
I made lots of things working from those.

The 'A' and 'B' designations were irrespective of physical size
(and the 'B' batteries covered a fairly wide range of voltage as well.)
I've used ones with 45V, 67-1/2V, and 135V. And, IIRC, the 'A'
batteries were the filament supply, 'B' for plate voltage, and 'C' (if
used) for negative bias supplies to get the filament closer to cutoff.
Most more recent tube circuits added a resistor in series with the
cathode, and bypassed that with a capacitor to provide a fairly stable
bias voltage, thus reducing the number of batteries (or supplies)
needed. This was termed "self bias".

Enjoy,
DoN.
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