[Amps] Push pull amps

[Carl]

Cross netralization is often a single band afair with plug in coils and home 
construction.

Parallel is far easier since the input can be swamped to burn off exciter RF 
as well as eliminate the need to neutralize.

Perhaps the primary reason for parallel is the ease of bandswitching, the pi 
network, and matching directly into that new fangled coax

Carl


----- Original Message ----- 
From: <sm0aom at telia.com>
To: <amps at contesting.com>
Sent: Saturday, August 01, 2020 5:34 PM
Subject: Re: [Amps] Push pull amps


> 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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