The plate voltage fluctuation is from line sag from another amp running the
160m contest. It may have been modulating the noise a bit, but didn't
appear to be the cause or a direct effect of the noise. I was also
concerned about the bias switching, but I did lots of tx/rx cycles with no
apparent triggering of the noise, nor did the noise start instantly after
going to rx when it did happen as I would expect shot noise from loss of
cutoff bias would occur, so a bad contact wouldn't seem likely. I'm still
looking though.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of gary@7-media.net
> Sent: Sunday, December 07, 2008 02:06
> To: amps@contesting.com
> Subject: [Amps] Fw: rx noise?
>
>
> ----- Original Message -----
> From: <gary@7-media.net>
> To: "K1TTT" <K1TTT@ARRL.NET>
> Sent: Sunday, December 07, 2008 3:04 PM
> Subject: Re: [Amps] rx noise?
>
>
> > Hi
> > '
> > Check your parasitic suppressor in the plate circuit. The symptoms you
> > describe point to the amp taking off.
> >
> > The fact the plate voltage was down a little suggests it is operating
> > whilst on receive.
> >
> > You may also have a bias relay contact problem. Often amps have a relay
> > contact that allows the bias to increase on receive and thereby turns
> the
> > tube off
> >
> > during receive and that may be a dirty relay contact etc.
> >
> > Cheers and good luck
> >
> > Gary ZL3SV
> >
> >
> >
> >
> >
> > ----- Original Message -----
> > From: "K1TTT" <K1TTT@ARRL.NET>
> > To: "Amps" <amps@contesting.com>
> > Sent: Sunday, December 07, 2008 4:11 AM
> > Subject: [Amps] rx noise?
> >
> >
> >>I have a commander hf-2500 (pair of 3cx800a7's, no qsk) that seems to be
> >> working fine. However, during cqww cw last week I had to pull it off
> the
> >> 20m station because it was making a broadband noise while on receive.
> I
> >> put
> >> it back on the station today and it isn't doing it now. I tried
> warming
> >> it
> >> up a bit and it still didn't do it....though its obviously not as
> warmed
> >> through as after 40 or so hours of cqww. The only other thing I
> noticed
> >> is
> >> when it was doing it the plate voltage dropped a bit, maybe 50-100v,
> but
> >> I'm
> >> not sure if that was a cause or effect since the line voltage sag from
> >> the
> >> other stations can make the hv sag a bit here. Any ideas where to
> start
> >> looking??
> >>
> >>
> >> David Robbins K1TTT
> >> e-mail: mailto:k1ttt@arrl.net
> >> web: http://www.k1ttt.net
> >> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >
> >
> > ------------------------------------------------------------------------
> --------
> >
> >
> >
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> 12/5/2008
> > 9:57 AM
> >
>
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