[Amps] Why does power output increase?

[Jim W7RY]

One also needs to make sure they are measuring the filament voltage with 
a true RMS voltmeter.


Most cheap meters wont do that.



Did you take a look at W8JI's site for measuring filament voltage. He 
does is successfully with drive power.


73, Jim W7RY



On 6/5/2022 6:04 AM, Victor Rosenthal 4X6GP wrote:
> I did measure the voltage at the tube pins. I haven't measured it 
> while transmitting, because the RF drives my meter crazy. I assume the 
> voltage drops a bit. Unfortunately I no longer have my trusty analog 
> voltmeter. I wish I did.
>
> I'll measure the line voltage. But the only thing I can think of that 
> would cause that to increase after long transmissions would be if the 
> breaker on the line heated up and lost resistance. I have never heard 
> of that!
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> CWops #5
> Formerly K2VCO
> https://www.qsl.net/k2vco/
> On 05/06/2022 6:19, Jim W7RY wrote:
>> *I'm curious Vic...*
>>
>> *See below"*
>>
>> On 6/4/2022 4:35 AM, Victor Rosenthal 4X6GP 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.
>> *Where did you measure this voltage. Best is to wrap a small wire 
>> around the tube pins, (all 3 of them) and measure the voltage at each 
>> tube.*
>>>
>>> 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.
>>
>> *I cant add anything about what your seeing... Other than is the line 
>> voltage changing?
>> *
>>
>> *73, Jim W7RY*
>>
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