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@gmail.com
<mailto:k2vco.vic@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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