[Milsurplus] BC-221 temperature compensating capacitor question -

[John Hutchins]

Oh grand wizards -
temperature compensating capacitor question
The BC-221-AK 1000Khz reference Oscillator has been observed starting 
about 220 HZ high, 4000.220KHz on cold start 4000.220 KHz then after 
about 2 hours of warm-up drifts down to about 20 Hz below 4000 KHZ at 
measured 3999.080 KHZ end of high band.  This found by finding the zero 
beat taking a frequency reading on the Freq counter then doing the same 
process periodically over a 2 hour period.  240Hz swing so far.

The temperature compensating coils are clean and can move freely, so 
that is not the problem.

Is this the norm expected considering the period in which the unit is made?

If not what considerations and procedures would  I use to re-compensate 
for the temperature environment.

Thanks
Hutch