I traced a similar noise to the 240V wall outlet. Over time the heating
and cooling from numerous contest cycles loosened the screws and
annealed the #12. I found it finally when taking the amp off the shelf
for the umpteenth time and noticed the plug was excessively warm.
Replacing the outlet solved the problem.
Carl
KM1H
----- Original Message -----
From: "David Robbins K1TTT" <k1ttt@arrl.net>
To: <amps@contesting.com>
Sent: Sunday, December 07, 2008 6:55 AM
Subject: Re: [Amps] Fw: rx noise?
> 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
>> >
>> >
>> > ------------------------------------------------------------------------
>> --------
>> >
>> >
>> >
>> > No virus found in this incoming message.
>> > Checked by AVG - http://www.avg.com
>> > Version: 8.0.176 / Virus Database: 270.9.14/1832 - Release Date:
>> 12/5/2008
>> > 9:57 AM
>> >
>>
>> _______________________________________________
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>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
> _______________________________________________
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>
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