[time-nuts] Re: Is SC the most stable cut for lowest phase noise?

[Ross P]

 I have seen that manufacturers seal their crystals in a vacuum, maybe air interaction affects Q. The point that vacuum inhibits heat flow is something I have never considered in ovenized units. My ovenized crystals take about an hour to settle. I have some WW2 surplus crystals in non-sealed packages that I have not tested... something to do.rp

    On Sunday, June 12, 2022 at 07:26:19 AM PDT, Louis Taber via time-nuts <time-nuts at lists.febo.com> wrote:  
 
 I have been of the impression for years now that most "better" crystals are
in a vacuum.  And the electrical and mechanical connections to the quartz
itself place as little mechanical load on the crystal as possible.
 Thermal conductivity from the oven to the crystal itself would be both
hard to model and hard to speed up.

IR transmission of energy to the crystal also seems problematic considering
the IR transmission of quartz and the IR reflectivity of gold
contact plating.

Is any of this an issue?

  - Louis

On Fri, Jun 10, 2022 at 9:53 PM Bob kb8tq via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi
>
> > On Jun 10, 2022, at 2:38 PM, Lux, Jim via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> > On 6/10/22 1:57 PM, Dr. David Kirkby wrote:
> >> On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >>
> >>Â  Â  On the subject of rapid warm up. I suppose if you had a need, one
> >>Â  Â  could
> >>Â  Â  dump as much power as you need into the heater. Turn on oscillator,
> >>Â  Â  lights in room dim for a few moments.
> >>
> >>
> >> Is that not likely to damage a crystal? Different parts of the crystal
> and likely to be at significantly different temperatures at the same time,
> putting a lot of stress on the crystal due to a thermal gradient. It's
> probably a bit academic, as nobody is going to make an oven that heats up
> in fractions of a second, but if one did, I suspect it might not do the
> crystal a lot of good. This is only an educated guess - I don't have
> anything to back it up.
> > Oh, it would be disastrous, although quartz is pretty strong, all the
> rest of the mounting components might not be.
>
> Indeed, breaking a quartz blank via thermal stress would be very hard to
> do.
> The “rest of the parts” actually are pretty durable as well. Most of it is
> metal and
> it is quite able to handle thermal issues.
>
> The big issue in a fast warm up AT turned out to be designing the heater
> and the
> mount to get the energy to the blank quickly….. If you use a small enough
> package
> and blank, the amount of power turns out to be surprisingly small.
>
> If you want to go bonkers, you mount the heaters *inside* the crystal
> package. This
> does indeed create some issues in various areas.
>
> Bob
>
> >>
> >> At the other extreme,  would there be any advantage in actually heating
> the crystal very slowly, over the course of an hour/day/week, so the
> temperature gradient across the crystal is very small? Of course, if an
> oven took ages to reach the correct temperature, it would be inconvenient
> for most applications, but for some applications, the advantages might
> outweigh the disadvantages. Of course, if one does this, I suspect one
> would have to cool the crystal slowly too to prevent a significant thermal
> gradient across the crystal.
> >>
> >> I know it's a bit different, but I have a 600 mm f4 Nikon camera lens.
> I was told that Nikon cools the front element over a period of 6 months to
> reduce stresses in the glass.
> >
> > Big glass mirrors for telescopes do the same.
> >
> >
> >
> >>
> >> Dave
> >
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