[Amps] Push pull amps

[sm0aom at telia.com]

Easier cross-neutralisation has been mentioned, but another major argument for push-pull,
especially at higher frequencies, is that it becomes easier to get the proper L/C ratio
as the circuit tuning and stray capacitances essentially are in series.

73/
Karl-Arne
SM0AOM

----Ursprungligt meddelande----
Från : k2vco.vic at gmail.com
Datum : 2020-08-01 - 20:08 (CEST)
Till : amps at contesting.com
Ämne : Re: [Amps] Push pull amps

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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