Neville Michie wrote: > Silicon rubber is quite transparent to water vapour, at least in the
I believe it is Viton, not silicone > concentrations that are > important to the HP 10811. The seal on the screw will only slow the > response of the oscillator to humidity. > Epoxy is a much better barrier but not perfect. Vapour barriers must > be perfect. My tests showed that epoxy has no effect whatsoever on humidity. Goes right through it, right away. Viton is certainly a lot better than epoxy. > Water vapour adheres to oxygen atoms, so has an affinity to all > metals which have an oxide film. > It will also adhere to quartz being SiO2. The glass frequency trim > capacitor is a good candidate for humidity sensitivity, > but so are all the insulating materials. Obviously, the first thing I tried was to replace the trimmer with a fixed capacitor. Didn't help. 30 years ago when the 10811 first went into production, the trimmer was a problem, but IIRC the problem was that lubricating oil migrated around causing slow drifing. That trimmer was replaced by one from another vendor. > Solder seals are good against humidity as are glass to metal seals. > The way to make a HP10811 immune to humidity is to seal it in a metal > container with glass leadthrough seals > after it has been flushed with dry nitrogen for a few days. > Another method is to seal a small quantity of P2O5 in it as a > humidity "getter". An added improvement is to wind > two platinum wires on a P2O5 containing fibre glass pad, and > electrolyse any water absorbed to oxygen and hydrogen gas > after it is sealed. > Vacuum tube sealing and evacuation works well. > cheers, Neville MIchie Rick Karlquist N6RK _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.