[time-nuts] Aging rate of crystals

Richard (Rick) Karlquist richard at karlquist.com
Mon Feb 18 12:31:34 EST 2008



Tom Van Baak wrote:

> Rick,
> 
> For these experiments did you remove the 10811 guts from the
> outer case? I realize the case is not sealed, but the air gap is
> very small; how could humidity get inside so rapidly?
> 
> Did you look into /why/ the 10811 was humidity sensitive? The
> resonator and most individual board components are sealed, so
> that doesn't leave too much. Maybe the coarse tuning variable
> capacitor, which is exposed to air through its 2 mm hole?
> 
> Do you know if most modern high-end OCXO, which are solder
> sealed, and which have no screwdriver tuning access hole, are
> immune from all humidity variations?
> 
> /tvb

I did not remove the 10811 from the case.  OTOH, I tried some
experiments with so-called "hermetic" epoxy.  I think I used
the 10811 version with the feedthrus in place of the edge connector.
I sealed all the holes and seams etc.  I am fairly confident
the oscillator was "waterproof", meaning you could dunk it
in a bucket of water with no ill effects.  In any event, what
I found was that the epoxy was not only not hermetic, but it
virtually didn't even slow down the frequency shift due to
humidity.  BTW, the individual board components are definitely
NOT sealed, being epoxy dipped or plastic molded.  Except for
the 2N5179 transistors and some of the glass diodes.

I am fairly certain that solder sealed oscillators are actually
hermetic and will not be influenced by humidity.

Rick Karlquist N6RK



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