[Amps] SB-220 saga continues

[Rex Lint]

This condition suggests there is a short in the keying circuit inside the
amp...

      -Rex-
 
K1HI
      Rex Lint
      Merrimack, NH 

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Don Moman VE6JY
Sent: Sunday, November 09, 2008 1:28 PM
To: Amps at Contesting. Com
Subject: [Amps] SB-220 saga continues

A friend locally described a very similar situation he is having with his
SB-220 recently.  I haven't seen the amp but I have a feeling I will.... It
has worked fine for many years until a few weeks ago.  I had him unplug the
keying line from the SB-220 and the problem still happens.  When the key
line is plugged back in he can still key the amp thru his 756 (and ext relay
box).   To me that just about defies logic.  Only grasping but if that small
bypass cap leaked just enough to partially lift the tx relay so the antenna
thru path went open, that might cause it but seems pretty iffy to me...

73 Don
VE6JY

>
> > >> Alfred Frugoli wrote:
> > >> > Hello everyone,
> > >> >
> > >> > So it seems I've got a problem with my SB-220.
> > >> >
> > >> > When the amp is off, but connected in the RF path,
> > >> everything is fine.
> > >> >
> > >> > When I switch the amp on I've suddenly got lots of attenuation
> > >> > happening on the receive path.  Transmit seems fine -
> > amp tunes OK
> > >> > etc.
> > >> >
> > >> > My first suspicion was that there were dirty relay
> > contacts on the
> > >> > receive side.  Cleaned the contacts with no success.  Then
> > >> I realized
> > >> > that the problem only occurs when the amp is on.  So a
> > trip to the
> > >> > schematic tells me I don't understand.  In the RX mode
> > the RF path
> > >> > through the amplifier should be the same as when the power
> > >> is on.  So
> > >> > I'm not sure where my attenuation is coming from.
> > >> >
> > >> > Just testing it a few minutes ago I can make an S5-7
> > station almost
> > >> > completely disappear by turning on the amp, so I've got
> > >> somewhere in
> > >> > the area of 20db of attenuation happening!
> > >> >
> > >> > Thoughts?
> > >> >
> > >> > Thanks.
> > >> >
> > >> > 73 de Al, KE1FO
> > >> >
> > >> > -----
> > >> > Visit my amateur radio contesting blog at ke1fo.wordpress.com.
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> > >> >
> > >>
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>
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