Steve's approach is an acceptable method to read the filament on a
common grid HF amplifier. The 10 K resistors would optimally be carbon
film or comp and not wirewound, so that they are non inductive and have
lowest capacitance from end to end. There will be RF voltage across it!
I would probably put a 10 nF cap to ground on each cold lead to the
meter as well, keeping all of that close to the resistors in an
enclosure in the amplifier. The capacitors should be mica with short
leads or quality ceramic. The resistors should be bigger than 1/2 watt
just for the RF voltage. Not for dissipation. Just remember to test it
with and without RF drive applied to see if there is RF affecting the
reading or not. An analog rms meter will likely ignore it.
73
John
K5PRO
On 6/5/22 10:00 AM, amps-request@contesting.com wrote:
1. Re: Why does power output increase? (Steve)
----------------------------------------------------------------------
Message: 1
Date: Sun, 5 Jun 2022 16:41:35 +0100
From: Steve <g8gsq72@gmail.com>
To: amps@contesting.com
Subject: Re: [Amps] Why does power output increase?
Tack a 10k resistor to each filament pin, 10nF decoupling between the
loose ends then twisted pair out to your DVM. Should filter out the rf
and you don't have to worry about shorting the wires together.
Steve G8GSQ
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/
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|