Tom W7WHY 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
Push pull is not gone, most rice boxes use a push pull final
amplifiers to this day.
Pros
1. Ease of neutralization (if you know how, it is called cross
neutralization)
2. Automatically suppresses (cancels out) the second harmonic. (and
fourth … )
3. If biased properly class "B" operation is the most overall
efficient mode.
Cons
1. Bandswitching tube amplifiers is cumbersome, requiring center
tapped coils
and dual (ganged) tuning capacitors. (Wideband transistor amplifiers
need
only wideband transformers.)
--
Ron W4BIN - Understanding is much better than
knowing how.
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