Rick,
I have used the open frame relays you describe in several remote tuner
projects over the years, and they worked really well. With the original contact
spacing and with 1500W power output I never observed any arcing problems. With
the stock relay spacing the voltage between the NO contacts breaks down at
around 6 kV. The impedance in question would have to be quite high to get there
at 1500W.
One of the other issues with them is hot switching the relays, and in turn
slowly destroying the contacts. (I have never done that of course).
I live close to the coast, and the biggest problem with my application became
corrosion. All of the exposed metal eventually corroded, so I migrated to HC-1
or RJ-1 vacuum relays for my antenna tuners and switching applications. I never
had one of these vacuum relays fail so far.
I have a fairly large stock (100+) of HC-1 or RJ-1 vacuum relays to pick from,
some NOS, some pulls. I HI-potted them all. Upon testing them I had many
failures, even the NOS ones, so anyone buying these relays better beware, you
could be buying junk! (Reminder to myself: sell the failed relays on e-bay,
as-is, condition unknown.) I also observed the breakdown voltage to be quite
different for similar relays, all over the place up to 6 Kv +. Most crack in
the 3.5-5 kV range, the ones under 3kV I don't use.
Comtek has been using a T92S11D22-12 in their later switch boxes. It is a
sealed relay with high current rating, and quite inexpensive. Allied has it
for around $11.
Niko - AC6DD
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