Date: Sat, 31 Mar 2007 23:08:42 -0700 (PDT)
Subject: Re: Topband: Vacuum relay powering #2
From: "Rick Karlquist" <richard@karlquist.com>
A possible argument in favor of Wolff's position:
I work for Agilent (used to be HP) and they used a LOT of reed
relays. They come in form A (SPST, NO), form B (SPST, NC) and
form C (SPDT). The form C relays need a permanent magnet to hold
the NC contact when not energized. IIRC, the energizing current
is the same between forms A, B, and C, (being limited by heat dissipation)
and the result is that the contact pressure is half as much for form C.
Back when we had component engineers and a reliability lab (before
they were all fired to save money) the expects told us that form
C was inherently less reliable than A and B, presumably due to the
reduced pressure. We were instructed not to use form C unless
absolutely necessary.
As I said before, DC/DC converters are easy to get and if you put
one in a metal box with some RFI filtering, it won't cause RFI.
The K6XX circuit puts EXTRA voltage on the relay during switching
and then cuts back to NORMAL voltage. It is not intended
to operate the relay at reduced current. AG6K has a similar
speed up circuit on his web site for a QSK vacuum relay. I built
his circuit and it is indeed VERY fast.
Rick N6RK
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