[AMPS] SB-220 conundrum

[Fisher]

Hi Pete N4ZR -

I can't help but wonder if you haven't had this situation all along and that
your new relays (or something to do with their installation) exposed it.

I call this a situation rather than a problem because those 40 M numbers
sound like something one might reasonably expect from a pair of 3-500's
being driven by 100W.

I know that you were accustomed to the dips in plate current to coincide
with maximum power output prior to this, and I certainly am too light-weight
to be able to get into that.  All I can say is the obvious which is we
usually tune for max output partly, at least, for that very occasion when
the two don't line up, but I don't know ramifications of that, yet - been
too busy just trying to get to a point where I can understand some portion
of the emails posted on this list.   If the plate current dip is not present
at max power out and if max power out is too high, then does that mean that
some garbage is being created and transmitted - and, in your case, rather
efficiently?

What do on air tests reveal?  It sounds to me like you could find out if
most of that output power is all on the fundamental frequency by just
transmitting key down and having someone try to precisely note the db
increase from 100W to 1450W.  So, what will it mean then if an exact 11db
increase is noted?  Beats me.  But if only a 6 db increase were noted, then
that would surely indicate a real problem.

I hope your respondents to this thread will post to the list or copy to me.
I have had more than my share of these kinds of weird situations.

73, Lu K5YP


----- Original Message -----
From: Pete Smith <n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Tuesday, January 18, 2000 16:19
Subject: [AMPS] SB-220 conundrum


>
> 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
>
>
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>


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