[Amps] HF amp output power dropping

[Pat Barthelow]

Last time I had this happen it was the antenna. I think something was
getting hot and changing the match. I am sure you are tuning it into a
dummy load, so it can't be that. However, it was possibly worth
mentioning. 
>     Mike
Good Idea, Mike, 

Try using a crossed needle Wattmeter/SWR meter to watch how/if the SWR changes in sync with the power drop. 
Also observe the plate CURRENT meter at the same time.

All the Best, 73,
Pat Barthelow     aa6eg at hotmail.com
http://www.jamesburgdish.org
Subscribe: http://bambi.net/jamesburg.html
Jamesburg Earth Station  Moon Bounce Team


> Date: Sat, 29 Sep 2007 22:06:48 +0100
> From: m.j.willis at rl.ac.uk
> To: amps at contesting.com
> Subject: Re: [Amps] HF amp output power dropping
> 
>     >> HAM use by someone else. It runs a 3CX3000A7 tube in
>     >> grounded grid.
>     >> Recently the output power has begun falling off rapidly
>     >> whenever I apply constant drive such as during tune up.
>     >> The tube is new and the plate voltage remains steady as
>     >> always.Is there anything else that could be causing this?
>     >> It reminds me of a tube that has gone soft although I am
>     >> sure it's not the tube.
>     >> Any help is appreciated
>     >>
>     >
>     Last time I had this happen it was the antenna. I think something was getting hot and changing the match. I am sure you are tuning it into a dummy load, so it can't be that. However, it was possibly worth mentioning. 
>     Mike