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Re: [Amps] Why does power output increase?

Subject: Re: [Amps] Why does power output increase?
From: Jim W7RY <>
Date: Sun, 5 Jun 2022 08:12:49 -0500
List-post: <>
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!

Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly 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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