[R-390] 2nd xtal osc temp control

[Perry Sandeen]

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