[time-nuts] Oscilloquartz 8601 Rebuild Question

[J. Forster]

I would avoid steel. It usually has higher thermal leakage than glass.

> I'm rebuilding an Oscilloquartz 8601 oscillator that has a smashed
> Dewar.  The 8601 is basically the same as an 8600, but with a different
> connector arrangement.
>
> Since I can't replace the original Dewar, I'm trying various vacuum
> flasks to see which one works best.  The differences are related to the
> size (how much room for a foam plug) and material (glass vs. steel).  Am
> I correct in thinking that 'best' means minimizing the current drain?

Yes, but you maqy not want to cut the leakage too much below what was
originally there. It could cause loop overshoot or instability.

> I'm thinking that minimizing the current drain means minimizing heat
> loss to the external environment and therefore most stable performance.

Only if the loop can handle it.

> Or should I try to match the thermal characteristics of the original
> flask and plug?  I could approximate this by adjusting the thermal
> characteristics to obtain the same current drain as stated in the
> specifications.

That will give you a static match, not necessarily a dynamic match.
Consider if you filled the Dewar with mercury.

> Of course, if you go too far in reducing the current, the oven could
> overheat.  The oscillator includes a precision thermistor to monitor the
> temperature of the oven to prevent this.
>
> Any comments?
>
> Ed

Good luck.

-John

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