[Amps] Why does power output increase?

[Victor Rosenthal 4X6GP]

1. I have often wondered whether the filament voltage should be measured 
under full power or in standby. I operate CW only, so even during a 
transmission, 50% of the time the voltage is at the key up value. And 
probably more than 90% of the time the amp is on, I am not transmitting. 
That means that the filament voltage would be high most of the time.

I guess the question is whether the high filament voltage condition 
during standby would reduce tube life -- or if slightly low voltage in 
key-down would be worse. Another interesting question!

2. See my previous message.

73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/
On 04/06/2022 15:23, Shane Youhouse wrote:
> Vic,
> 
> 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 <k2vco.vic at gmail.com 
> <mailto:k2vco.vic at gmail.com>> wrote:
> 
>     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
>     https://www.qsl.net/k2vco/ <https://www.qsl.net/k2vco/>
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