[Boatanchors] 1930's era cw transmitter

[bcarling@cfl.rr.com]

Push pull operation the easiest to neutralize? Not!

In my experience it was impossible to neutralize. I had to give up and sell a Globe King 400  that had p-p triodes.
Impossible to tame.

Bry Carling


----- Reply message -----
From: "KA4INM" <ka4inm at gmail.com>
To: <boatanchors at mailman.qth.net>
Subject: [Boatanchors] 1930's era cw transmitter
Date: Sat, Jun 1, 2013 9:06 pm


  On 06/01/13 20:20, Brian Clarke wrote:

> Push-pull RF PA for AM at HF is most unusual. Most designs, including Dr
> Drake's ARC-5 and its clones, Collins, General Dynamics and Harris put
> RF tubes in the PA in parallel.

  Most 100 Watt "rice box" rigs use an output circuit of push pull design.
This reduces the idling current and suppresses the second harmonic output.
AM broadcast transmitters that used push pull RF amplifier circuits were able to get twice or three times the tube life out of a pair of tubes of parallel operation.

> Why? In push pull, each tube is working half the time - so you won't get
> 100 W input, let alone output. In parallel, both tubes are working all
> the time. And the killer? Neutralizing push-pull is a bear - so much
> easier in parallel designs.

  With push pull operation you can operate each tube at twice the current and with two tubes (or transistors) get out twice the power of one tube.  Push pull operation allows linear operation with a minimum idling current/power.

  Push pull operation allows "cross neutralization," the easiest to design and implement.

> The RCA Transmitting tube manual lists 60 W maximum input for CW as ICAS
> operation for the 807 - less for CCS and for telephony. But if you are
> in the land of plenty and you can afford the time to keep neutralizing
> the tubes you melt, go right ahead.

  Once a circuit is properly neutralized it is neutralized on any frequency.
The adjustment is based on capacity, not frequency.
-- 
  Ron  KA4INM - Youvan's corollary:
                Every action results in unwanted side effects.
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