I do not use this amplifier QSK, and have it set up with a speed-up circuit
in any case. Normally, I run 20-30 Ms of PTT delay to protect the relays,
but that's not really practical with hand keying. I may have been doing
some hot switching. The output relay is an HC-1
Thanks for the confirmation.
73, Pete N4ZR
At 10:34 AM 11/22/2004, R.Measures wrote:
On Nov 22, 2004, at 7:02 AM, Pete Smith wrote:
I modified my SB-220 about 5 years ago with vacuum relays on the input
and output. It has had a lot of hard contest use since then without
incident, but this weekend, after about a half hour, I noticed that I was
intermittently getting no output from the amp, even though the
transceiver looked like it was putting in normal drive. It seemed to
change from one switching cycle to the next -- sometimes it would go a
dozen QSOs with no problem, but on the 13th nothing was getting out.
About an hour after this started, the input relay (a Hi-G d'Italia
surplus job) started not closing intermittently, leaving me with no drive
either, so I shut the thing down altogether.
I have replacement relays on the way, but would like to tap the
experience on the list -- does this sound like just contact failure,
Yes, Pete. A vacuum relay equipped amplifier that is used with a modern
transceiver is at risk of hot-switching if it does not make faster than
the transceiver. Cu-contacts are especially vulnerable to erosion from
hot-switching. Since modern transceivers typically begin to produce RF in
5 - 8mS, only a few vacuum relays are capable of switching fast enough --
and even then, a speed-up circuit is needed to initially overwhelm the L
in the relay's coil. Satisfactory relays for this job are the Jennings
RJ-1A and the Kilovac HC-1. In order to get enough speed-up, 3 - 5x the
coil V needs to be available during make.
http://www.somis.org/D-a-07B.jpg
...
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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