[Amps] Why does power output increase?

[Victor Rosenthal 4X6GP]

Yes, I found it here:
<https://www.w8ji.com/filament_voltage_life.htm>

He notes that the Eimac specs for the 3-500Z call for 4.75-5.25v.

What I should do is check my line voltage (it is usually pretty close to 
230 here) and measure the voltage at the tube pins in standby when the 
line voltage is at the highest expected value. Then adjust it to be just 
under the maximum value. That way when it drops, it will be more likely 
to stay above the minimum.

So by setting it to 5.0v in standby I have been doing it wrong all 
along! Probably 5.2v would be a better choice.

73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/
On 05/06/2022 6:25, Jim W7RY wrote:
> W8JI has some filament voltage measurements for the AL80B on his web 
> site and how he measured it under load.
> 
> 73. Jim W7RY
> 
> 
> On 6/4/2022 8:51 AM, Victor Rosenthal 4X6GP wrote:
>> 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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