Topband: Engineering ?? @ relays

[Larry Higgins]

> > So how does Ameritron get reliable connections?  And Com-Tek with their
> > phased arrays?  Are relays unsuitable for this application?  Should the
> > contacts be gold?  What am I missing here?
>
Back in the days before digital tv tuners, when channels were selected by
mechanical switches, contact oxidation was an ongoing problem.  I worked for
a tv shop for a few years back then.
Tuner cleaning was probably our most frequent repair service in those days.
There were chemicals on the market for cleaning them.  They fell into two
categories: either the can was marked "leaves no residue" or "leaves a
protective residue" or similar wording.  We found that if the contacts were
heavily corroded the no residue cleaners were somewhat better for cleaning.
But if we used only the no residue type, the tv was likely to be returned
for another cleaning within a short time.  If we used the residue type, we
didn't see it again for several years.The residue type also works well for
carbon potentiometers.

 I've since cleaned literally millions of contacts and controls with
excellent  results.  The residue is sometimes called a lubricant and in fact
probably is one.  But I think its more important attribute is that by
coating the contact with a film, air cannot get to the metal.  No air, no
oxidation.

Just about every  electrical or electronics distributors, or places like
Radio Shack, still sell both types.  Use the residue type and there should
be no further problem for a long time to come.

Incidentally, my amp uses a very large open frame relay for changeover.
It's been at least five years since I cleaned its contacts.

73

Larry, N9DX



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