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Re: [Amps] Push pull amps

To: Victor Rosenthal 4X6GP <>,, "Tom Osborne Sr." <>
Subject: Re: [Amps] Push pull amps
From: "Mark, K5AM" <>
Date: Sat, 1 Aug 2020 19:53:20 +0000
List-post: <>

Push-pull is a nice method. The link below shows
a push-pull amp I built 59 years ago; it still runs
full power with the original Eimac tubes.


Mark, K5AM

On 2020-08-01 18:08, Victor Rosenthal 4X6GP wrote:
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.

Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
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
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