Some of you might recall I posted a problem on receive with my Alpha
77Dx.... suspecting the RJ1-A vacuum relay, of course.
Original message:
Subject: [AMPS] Alpah 77DX rcve bypass problem
Lost the receive path somewhere in the Alpha 77DX just before the end of
the WPX test this past weekend. The direct/aux slide switch has been
by-passed so that isn't the problem. Transmit works fine. receive had
always worked fine before.
What I've seen so far: Antenna is routed fine from a cold start and thru
the 3 minute warmup. The first time it keyed it after that, it took a 1/2
second or so to get rcve back, next slightly longer and then quickly
refusing to work after that. Thumping the case had no effect. If you shut
the amp off, the rcve will come back in a few (5 to 15) seconds maybe.
What to suspect? Well the vacuum relay is about the only thing in the
path. So measuring the pull down point (Q301) on the QSK board showed that
to operate fine (55 volts pulled low when keyed, then comes back up
quickly). I thought if something was leaking here it might keep the relay
switched in tx, but that doesn't seem to be the case. Yet something is
keeping it energized as shutting the amp off lets the relay go back to
receive.
I haven't a spare vacuum relay to pop in, but that seems like the obvious
thing to do, but in the meantime, anyone have any other thoughts? Residual
magnetism holding it on or??
---------------------------------------------
end of original message
Thanks to all (and there were quite a few) for their constructive ideas. I
haven't replied up till now, as I wanted to give the amp a shakedown test
in the contest before reporting anything..... I did go as far as
reversing the leads to coils, with no change in operation. I did not
attempt to degauss the relay. To shorten the story, a "new" relay was
installed and it worked fine all during the last Canada Day (full 24
hours) contest.
The original relay behaves fine on the bench, simply switching in a small
light bulb - tried many times with no failures. I do not have access to a
hi-pot so I can't test too much further. Whatever the problem was, I'm
still not exactly sure, except that the amp works fine now. There must be
some deficiency with the old RJ1A as I'm quite sure there was no
intermittent gremlins floating around, the relay wiring was all original
and very well done.
I bought the amp maybe 8 years ago (s/n 2986) but I have no idea how much
use it got before me (I suspect not much). Here it has operated most
major and many smaller contests, lots of CW but rarely any full break in.
73 Don
VE6JY Don Moman email: ve6jy@freenet.edmonton.ab.ca
Box 127 Lamont, Alberta email forwarding: ve6jy@rac.ca
CANADA T0B 2R0
(780) 895-2925
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