Yes, looks like that's a good bet. I just read the manual section on how
the dynamic bias works. There's a third set of contacts on the RF switching
relay that affects the bias. Looks like if that contact is not opening,
then the normal operating bias would be applied to the tube, hence the
100ma., which should be the normal idling current AFTER the first RF appears
from the exciter. If the contact does open, a higher bias would be applied,
cutting of the tube. I suppose a failure in capacitor C138, a bypass on the
bias line to the relay, would have the same effect as the relay not
opening.
K8AC
Floyd Sense - Angier, NC
----- Original Message -----
From: "measures" <2@vc.net>
To: "Floyd Sense" <sentek@sprintmail.com>; "AMPS" <amps@contesting.com>
Sent: Thursday, May 10, 2001 17:38 PM
Subject: Re: [AMPS] AL-80b PROBLEM - ANY IDEAS?
> >
> >Just developed a problem in my AL-80B, and not sure what's going on.
When
> >operating SSB or CW, all is well and has been since I got the amp last
year.
> >I'm getting back on RTTY and was running some tests with the new
transceiver
> >when I noticed this problem.
> >
> >I key the TS-950SDX in FSK mode with about 40 watts output, driving the
> >AL-80B to about 400 watts out on 14.080 into a dummy load. If I unkey
the
> >transceiver within a few seconds, everything returns to normal in receive
> >mode. However, if I leave carrier on for 15 seconds or so and then
return
> >to receive, I hear the relay drop in the linear, but I still have 100ma.
of
> >plate current and a resulting orange glow on the plate. Turning the XMT
> >switch on the AL-80B to STBY makes no difference. I have to turn off the
> >linear in order to get things back to normal. Perhaps a failure in the
> >AL-80B bias circuit?
>
> * perhaps the bias relay is sticking? To find out, measure the fil. CT
> to gnd V.
>
> good luck, Floyd.
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
>
>
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