I would suspect the HV diodes rather than the filter caps. You did say there
was plate voltage fluctuations?
73
Jim W7RY
----- Original Message -----
From: David Robbins K1TTT
To: 'Amps'
Sent: Saturday, December 06, 2008 3:46 PM
Subject: Re: [Amps] rx noise?
I really, REALLY hate intermittent problems like this... it wouldn't do it
cold. So I started warming it up, after 1/2 hour or so I got the
transformer up to 225f, the rf deck surface about 150f, the tubes about
130f, the case was nice and toasty... and I got about 15 seconds of noise
from all of that. It may have been modulated a bit by line voltage
fluctuations from the 160m contest op on the next station, but wasn't
dependent on it. There was no measurable grid or plate current when it did
it. I did get to cycle the stby/op switch a couple times and the noise
dropped but didn't go away when I went to stby... so perhaps it could be
something in the control board oscillating when it hits some particular
temperature, but its darn hard to reproduce.
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: Joe Subich, W4TV [mailto:w4tv@subich.com]
> Sent: Saturday, December 06, 2008 18:54
> To: 'K1TTT'
> Cc: 'Amps'
> Subject: RE: [Amps] rx noise?
>
>
> Check the bias switch (relay, transistor, ?). If cutoff is
> not being applied in receive, the tube will generate wideband
> noise ("shot" noise).
>
> 73,
>
> ... Joe, W4TV
>
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> > [mailto:amps-bounces@contesting.com] On Behalf Of Paul Kraemer
> > Sent: Saturday, December 06, 2008 12:57 PM
> > To: n8de@thepoint.net; K1TTT
> > Cc: Amps
> > Subject: Re: [Amps] rx noise?
> >
> >
> > How about from a zener diode in a bias supply.
> > They make dandy noise generators and were the source of
> > widband rf for the
> > old Omega noise bridge. The current to make noise is
> > critical, line voltage
> > upset could put it at that point?
> > Just fuel for thought.
> > Paul K0UYA
> > ----- Original Message -----
> > From: <n8de@thepoint.net>
> > To: "K1TTT" <K1TTT@ARRL.NET>
> > Cc: "Amps" <amps@contesting.com>
> > Sent: Saturday, December 06, 2008 11:24 AM
> > Subject: Re: [Amps] rx noise?
> >
> >
> > > Dave,
> > > Sounds like a leaky power supply capacitor. Might be a cold solder
> > > joint in the capacitor chain. Good luck
> > > Don
> > > N8DE
> > >
> > > Quoting K1TTT <K1TTT@ARRL.NET>:
> > >
> > >> 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
> > >>
> > >
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps
>
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