Tetrode amplifiers for SSB using 4-400A were popular in early 60's.
They had a good following for high level AM, (used a the class C rf
stage and the PP modulator) and Eimac wrote some very extensive app
notes for them. I support GG triodes hadn't really matured into the
standard 3-500Z circuit yet.
The Johnson Thunderbolt: we have one at work for use as a general
purpose driver for experiments. It runs pair of 4-400As in AB2 -- yes
thats a 2. So grid current is drawn. The Heathkit Chippewa KL-1 used
a pair of the same tubes in AB1, and was better load for the exciter
stage. Both amps had a resistive input position and tuned circuits
that were selected by band. The Thunderbolt stuck the iron in the
same box, making for one heavy amplifier. Also it was QUITE ugly, in
my own opinion. See Electric Radio magazine for more info.
I was in WA last week and finally looked at a Chippewa. It was a
heavy duty unit compared to SB220, but had a screamer blower. I
wanted one to convert to plate modulated AM. This one had been
converted to grounded grid/grounded screen and cathode driven with
very little input tuning if any. Unfortunately all the original input
tuning circuitry for grid drive were removed and gone. Making a high
level plate modulated TX with cathode drive requires modulating the
driver stage as well. Oh well.
73
John
K5PRO
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