Take a real good look at the plate RF choke - you may find it has been
overheated and there are more than a few turns that are shorted together
because the insulation has melted off the wire. That would result in too
low an inductance with the bypass capacitor at the base just shunting RF to
ground on 80 meters, but enough inductance to still function well at higher
frequencies.
The solution would be to just pull off the enameled wire and rewind it with
the same number of turns with the same size wire.
Al - K8EUR
----- Original Message -----
From: "R.Measures" <r@somis.org>
To: "Bridges Donald T Capt 92 ARW/HC" <donald.bridges@fairchild.af.mil>;
<Ka7lpo@aol.com>; "AMPS" <amps@contesting.com>
Sent: Saturday, February 28, 2004 1:15 AM
Subject: RE: [Amps] SB-200 80 Meter dilemma
> The bandswitch contacts may have been toasted. The fixes are: replace
> the burned contacts, or replace the switch wafer.
>
> >Sir,
> >Thank you for your advise. I will try your suggestion. For
> >clarification, are you suggesting that the switch contacts need repaired
> >and/or the DC-blocker cap may need replacing?
> >Don
> >
> >-----Original Message-----
> >From: R. Measures [mailto:r@somis.org]
> >Sent: Friday, February 27, 2004 3:40 AM
> >To: Ka7lpo@aol.com; AMPS
> >Subject: Re: [Amps] SB-200 80 Meter dilemma
> >
> >** Sounds like the 80m Tune-C padder cap switch contacts have been
> >evaporated by occasionally arcing when they are open (40m - 10m). The
> >arcing is apparently caused by an intermittent VHF parasite. To find
> >the
> >frequency of the parasitic oscillation, unplug the amp and measure the
> >resonance present at either side of the DC-blocker cap.
> >
> >>I own the SB-200 amp. It operates fine on 40-10 meters. I have two well
> >worn
> >>tubes. But the amp does not want to function properly on 80 meters. On
> >80
> >>meters the amp indicates proper plate current but very low grid
> >current.
> >>On 80
> >>meters the amp puts out a minimal 150-200 watts as indicated on my watt
> >
> >>meter and
> >>then drifts down while exciter power is applied. Any thoughts on
> >diagnosing
> >>the problem or leads I might pursue?
> >>
> >>Help,
> >>Don
> >>_______________________________________________
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> >>Amps@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/amps
> >>
> >
> _______________________________________________
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>
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