SB 200

[David Wilson]

Hello John,

I would guess that the reason the output is down on 10 meters is more of
a design problem, than that of a tube problem.  I know that is the case
on the SB220 amps.  The relay adds a significant amount of inductance
and loss to the output capability of the SB220, and I would guess that
a similar arrangement was in the SB200 (even though the tubes and design
are not quite the same).

The fellow from Harbach (sp) electronics could probably confirm this.
I made several mods to my SB220 many years ago (back when the dinosaurs
roamed the earth :-) ) that made the difference between 500 watts out
on the SB220 and around 1300 watts (maybe more) on 10 meters.

If memory serves me correctly the 200 had a similar inductance problem
in output switching that caused the output to be down substantially on
10 meters.

In my case, I did some modifying to the way that the relay was constructed
to remove the sharp loop that goes to the contacts on the relay base.
I ran a new (larger flat and straight) line to the output coax from the
wiper contact.  Seems there were some other mods done (soft start, bias
changes, adding equalizing resistors across filter caps) to improve
the reliability of this particular amp.

Dave


John Barkow wrote...
>
> Hi Gang:  I am thinking about putting new finals in my Sb 200 and note that
> they are gertting haarder to find.  I have installed the new PS board and
> soft key and the amp is working fine but output is low on 10 meters--only
> about 200 watts while the other  bands run aboutg 450 to 500 watts.  Since
> these tubes are mounted horizonta. which brand of replacements shouldl I use
> and where are they available?  Thanks,  John Kd6pt
>
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--
David R. Wilson  WB4LHO
World Wide Network Services
Nashville, Tennessee USA
david at wwns.com

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