[R-390] 2nd xtal osc temp control

[Larry H]

You are absolutely correct, Jacques.  The only thing is that the normal
mode of operation is with the oven switch off and that turns off the 2nd
crystal osc oven, also.  Unless the circuit has been modified.  I'd say
that the usual temp of it after warm up is about 30 degrees C, that is not
any where close to the correct temp for those crystals.  My experience with
the 17 MH 1st osc running at 55 degrees C is that it is the same stability
as running it at the prescribed 75 degrees.  Perhaps the temp curve has
changed with age as the crystals frequency has.  I have  not tested for
that and not sure I can.

Regards, Larry

On Sat, Nov 2, 2019 at 8:33 AM Jacques Fortin <jacques.f at videotron.ca>
wrote:

> Hi Larry, Perry, group,
>
> I am sorry, but it is not as simple as that.
> When Xtals are made to be used in an oven, the cut angle in the raw crystal
> have to be selected to minimise the drift around the oven temperature, not
> around the ambient or any other temperature.
> If the R-390/390A crystals were originally made to have a "flat"
> temperature
> characteristic around 75C, moving the oven operating point by
> re-calibrating
> the thermostat may not yield to the best results...
>
> 73, Jacques, VE2JFE
>
>
> Perry, Good point on the temperature of the ovens and I agree with you.  I
> found an ovenaire 55 degree 2 crystal plug in one that I'm using, but I
> don't see how to adjust the 2nd osc temp.  How is that done?
>
> Regards, Larry
>
> On Fri, Nov 1, 2019 at 10:23 PM Perry Sandeen via R-390 <
> r-390 at mailman.qth.net> wrote:
>
> > Yo Bubba Dudes!,
> > The thermostats used for the VFO and 2nd xtal osc circuits are
> > commercial ones that can be adjusted over quite a wide range.  75C is
> > 167F and is not good for longevity of any circuits.  Try adjusting it
> > down to a much lower temperature. All the xtal box needs is a
> > temperature just a bit higher that the receiver chassis gets during
> normal
> operation for stability.
> > If that doesn't work one could consider a simple thermistor
> > proportional heater circuit if your are a Heretic like me.
> > Regards,
> > Perrier
>
>