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@telia.com>
To: <amps@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@gmail.com
Datum : 2020-08-01 - 20:08 (CEST)
Till : amps@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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