Pete,
It is generally accepted that if max. power output does not
co-incide with the plate current dip, you have a parasitic
oscillation. Why such a subtle change causes it is anyone's
guess.
Mike, W1NR
Pete Smith wrote:
>
> Here's a weird one for the group.
>
> I replaced the T/R relay in my SB-220 with a pair of vacuum relays -- an
> HC-1 on the output side and a tiny Hi-G d'Italia on the input side. It
> works great, but there is one anomaly. The input SWR on 40 meters (only)
> is high (~2.2:1) and this seems to be paired with abnormally high plate
> current and output power. All other bands are fine. Just for fun, I tried
> bypassing the input relay entirely, but that had no effect on the input
> SWR, so I'm inclined to think the relays aren't the problem.
>
> Running into a dummy load at ~ 1.1:1 SWR and using my HM-102 wattmeter (no
> Bird, but power levels presumably indicative, at least relative to each
> other), I find the following:
>
> 1. power output is ~1100w on 80, declining to ~950w on 10, all with the
> exciter showing 125 watts output and the SB-220 grid current ~200 ma.
> Plate currents are ~750 ma.
>
> 2. But on 40m, power output (PLATE and LOAD tuned for maximum) is ~1450w,
> grid current ~250 ma. and Plate current ~900 ma. There is also a fairly
> striking difference between the PLATE setting in this condition and the
> setting for minimum plate current. If I tune the PLATE for minimum plate
> current and LOAD for maximum output, the figures look much more like those
> on the other bands.
>
> Any idea what's happening? I find it hard to equate higher input SWR with
> apparently higher gain.
>
> K9MA has suggested that in any case it would be a good idea to re-do the
> input tanks on all bands to raise the Q and improve the SWR, and has kindly
> given me values that he has tested in his amp, but before I embark on all
> that I'm curious what people think about this specific situation.
>
> 73, Pete N4ZR
>
> Don't forget to update your entry in the World Contest Station Database
> http://206.102.70.3/search.htm
>
> --
> FAQ on WWW: http://www.contesting.com/ampsfaq.html
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
--
**************** Give Every Man His Dew **************
Michael A. McCarthy, President
Everest Engineering Corporation, Consultants
4 Barnes Circle, Marlborough, MA 01752
(508) 460-6737, FAX (508) 460-7951
mailto:w1nr@eecorp.com
******************************************************
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|