During the years I was running 10-40M stacks I used 24VDC surplus DPDT
relays at .50-1.00 each from All Electronics; 12 or 13A contacts if I
remember and in clear plastic dust covers. These were mounted in surplus
CATV line fixtures (splitter, power combiner, etc).
After up to 15 years of heavy use when I dismantled the arrays they looked
still as new inside and never once acted up.
IMO there is way too much fussing about things that have no effect at HF to
most users.
Note also that all Ameritron switches use open relays, even the overpriced
ones.
The supposedly idiot proof RCS-12 would be attractive at certain contest
stations with operators still with training wheels.
Tom still hasnt answered why there is only a $10 price difference between
the RCS-4 and the -8V yet users of the -8V are getting raped for replacement
relays.
Carl
KM1H
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "Stan Stockton" <wa5rtg@gmail.com>; "Milt -- N5IA"
<n5ia@zia-connection.com>
Cc: <topband@contesting.com>
Sent: Friday, October 10, 2014 8:29 AM
Subject: Re: Topband: TX relays
I have built four or five "stack matches" using these relays and have
been quite pleased with them.
http://www.mouser.com/ProductDetail/TE-Connectivity/T92S11D22-12/?qs=%2fha2pyFadujQKxyiQ9QJsU9gOmzykpctnwthD3xoZjoJPHbNrun4hw%3d%3d
73...Stan, K5GO
If you look at the contact material, it is the wrong material type for our
applications. Those relays are hot switch relays for high current
applications with Silver Cadmium Oxide. From an engineering bulletin on
selecting relay contact materials:
Silver Cadmium Oxide
Silver cadmium oxide contacts have long been used for switching loads
that produce a high energy arc. Silver cadmium oxide contacts are less
electrically conductive than fine silver contacts, but have superior
resistance to material transfer and material loss due to arcing. They do
exhibit greater interface resistance between mated contacts, and also a
slightly greater contact assembly heat rise. The minimum arc voltagerating
of silver cadmium oxide is 10 volts and, like fine silver contacts, the
silver
in this alloy will oxidize and sulfidate. Therefore, an arc is necessary
to
keep these contacts clean.
This doesn't mean they won't work and will go up in smoke. It does mean
they are subject to contact sulfidation which causes intermittent receive.
They have silver, a hard base material, and large contact area that does
not wipe well. They also are the type of relay that is subject to contact
derating from skin effect because of constant resistivity.
73 Tom
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