[Amps] Push pull amps

[Ron W4BIN Youvan]

    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.