[R-390] VFO End points, pressurization

[Tisha Hayes]

I would of been really surprised if any of the VFOs still have positive
pressurization left in them. The little O rings may be in decent shape but
still, we are talking about +40 years.

Lots of electronic/avionic gear was pressurized with a purge gas like inert
nitrogen. Theoretically the mechanical filters had that at one time as
well. The goal was to keep a semi-controlled atmosphere at a positive
pressure so moisture would not affect the circuitry. For avionics there was
also a need to minimize corona discharge from a rarefied atmosphere (low
pressure arching, the same thing can happen in spacecraft).

If there was going to be a leak, it would be outwards and not in a way
where humidity would be sucked inwards. Other devices like the R-392 were
supposed to be pressurized as well. I have not heard of many exploding
R-392's over the decades and that would be a much larger volume of gas.

If you are going to crack the case on the VFO to do work at least clean up
and lube the O rings and cover with something like a very thin touch of
silicone grease (more is NOT better). I also would not reassemble the VFO
outside in the middle of a jungle or in your shower stall. Try to keep
moisture out of the electronics before you button it back up.

-- 
Ms. Tisha Hayes/ AA4HA

"Objective considerations of contemporary phenomena compel the conclusion
that success or failure in competitive activities exhibits no tendency to
be commensurate with innate capacity, but that a considerable element of
the unpredictable must invariably be taken into account." -- George Orwell