I think the main reason they liked putting triode amplifiers in
push-pull was to simplify the neutralization. Of course it is possible
to neutralize single-ended amps with a bridge circuit or to use
inductive neutralization, but I think it's easier to obtain complete
neutralization with a push-pull circuit.
The change came about with the popularity of tetrodes which are easy to
neutralize in single-ended configuration, the popularity of pi-network
output circuits, and the desire to get away from plug-in coils (think
about bandswitching a balanced tank circuit). Also, TVI shielding was
difficult with plug-in coils.
I think probably the change happened after WWII, when surplus coax
became available. Shielded, single-ended circuits with pi-networks
running into coax-fed antennas became the hot setup.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 01/08/2020 20:02, Tom Osborne Sr. wrote:
I recently purchased some QST's from '47, 49, and 50. I notice a lot of
transmitters and amps back then used 2 tubes in push-pull circuits, instead
of parallel, like we mostly do now.
What was the idea behind push pull compared to parallel, and when did the
change take place? Thanks and 73
Tom W7WHY
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