[R-390] Apologies and R-390A Power Swictch Question

[Jan Skirrow]

Hi Robert ...

You're likely going to have to replace the switch, and Morris Odell's
approach is probably better than buying a replacement switch from Fair
Radio - assuming they have any left, they may be near then end of their
lives too.

I find it interesting that these things fuse shut. I suppose I thought the
arc on opening would - over time - build up enough material to bridge the
contacts. Yet when I repaired one of mine, the fused contacts showed some
arc damage, but other than being fused together, they were fine. When they
were separated, the moving contact sprung right back, leaving a nice wide
gap.

I thought at the time that the arc on opening was definitely damaging the
contacts. But I became convinced it was the surge on closing that welded
the damaged (and thus more susceptible) contacts together.

I've thus installed current inrush limiters on the R-390As that I've
rebuilt. I've had no further problem with the original microswitch that I
repaired. Maybe these two things are connected. Who can be sure? At the
time I thought it might be useful to put an arc suppressor on the switch to
protect against the contact opening problem, but have yet to do it as I've
not had another failure (knock wood!).

Jan Skirrow, VE7DJX

Duncan, BC, Canada

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