[time-nuts] Double ovened 10811-60158 on ebay

Rick Karlquist richard at karlquist.com
Sun Jul 20 15:42:57 EDT 2008

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

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