[Amps] SB-200 80 Meter Dilemma Update

[carl seyersdahl]

When it comes to the SB200, or for that matter any other amp, 80 mtrs seems
to be a difficult band to get a decent input swr.
 What is your input swr , more or less exactly, on 80.???  I have had many
cases of troubles on 80 with the input swr.
  Of course, there are other possible problems, but on the sb200 (etc) it
can get
 troublesome. I'm not the ultimate guru on sb200's (or any other) but I've
been thru a few 200's. (oh, what fun )
    carl / kz5ca
----- Original Message ----- 
From: "R.Measures" <r at somis.org>
To: <Ka7lpo at aol.com>; "AMPS" <amps at contesting.com>
Sent: Thursday, March 04, 2004 5:47 AM
Subject: Re: [Amps] SB-200 80 Meter Dilemma Update


>
>
> >Here is an update on my 80 meter dilemma on my SB-200. Originally, I
posted
> >that my SB-200 was working great on 40-10 meters but not good on 80. I
had a
> >high swr and any noticeable power output above 150-200 watts immediately
> >dissipated.
>
> **  This suggests that your drivermight be throttling back to protect
> itself.
> >
> >The load and tune Caps (both the 100 pf and 500 pf caps) test good. No
> >apparent damage to bandswitches. The Plate choke looks good.
> >
> >I inspected the tuned input C30 cap and added an additional 200 pf to the
> >470
> >pf mica cap. My swr on 80 meters is now much improved. I now have
noticeably
> >greater output power BUT the power still quickly dissipates or diminishes
> >while keyed down. It peaks then quickly drops.
> >
> **  strange
>
> >Are my grid-ground caps off both tubes suspect? I do have two well worn
> >tubes that show excessive heat damage. Can the 572B tube work great on
40-10
> but
> >become dysfunctional on 80?
>
> **  No.
> -   I would try a Pi-network 80m tuned-input with a Q of 2.  (Xc!=25-ohms)
>
> good luck, Don
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