[Amps] Why does power output increase?

[Adrian]

That's a good take on a likely reason.

A voltmeter across the resistor then monitored, would confirm it,

if VD drops.


vk4tux

On 4/6/22 22:23, 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>
> 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/
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