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Re: [Amps] Why does power output increase?

To: Shane Youhouse <>, Victor Rosenthal 4X6GP <>
Subject: Re: [Amps] Why does power output increase?
From: gudguyham--- via Amps <>
Reply-to: "" <>
Date: Sat, 4 Jun 2022 13:26:32 +0000 (UTC)
List-post: <>
I agree with Shane and was exactly my thought, however resistors usually go up 
in value when they get hot.  I would get rid if that resistor faster than you 
can say Rumpelstiltskin.  

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On Saturday, June 4, 2022, 8:23 AM, Shane Youhouse <> wrote:


1.  You want 5.0 volts under full bore TX, not at receive.

2.  I'd suspect the filament primary resistor.  If it's heating up and
dropping resistance, more current will be allowed through.  This will cause
the voltage on the filaments to rise su sequently increasing emissions from
the tubes.

Is the resistor in the airflow to keep it cool?

--WP2ASS / ex KD6VXI

On Saturday, June 4, 2022, Victor Rosenthal 4X6GP <>

> This isn't a problem, just a phenomenon that I would like to understand.
> I have a TL922. Mods include directly grounded grids. I also measured the
> filament voltage with my Fluke true RMS meter and put a small resistor in
> the primary of the filament transformer to provide exactly 5.0v in standby.
> It has been running with the same genuine Eimac 3-500Zs in it for about 6
> years.
> So here is what happens: after a longish CW transmission, the power output
> INCREASES. On 20m, for example, it may go from 1200 to 1400 watts. When it
> cools, the power drops back.
> I've noticed this with several wattmeters. I have observed no change in
> SWR when this happens (it's 1:1 thanks to a Johnson KW Matchbox).
> It happens when the amp is driven with an Elecraft K3 and also a TS890s.
> I'm interested in hearing theories about why this might occur.
> --
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> CWops #5
> Formerly K2VCO
> _______________________________________________
> Amps mailing list
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