[Milsurplus] BC-221-AK Beating a dead horse with more questions

[John Hutchins]

Group -
I apologize for beating a dead horse BC-221-AK.  But this has been my 
re-ed-u-ma-cation project.

On Page 146 paper manual TM11-300 or page 159 in PDF the 6pF part number 
5; it is not noted as a temperature compensating capacitor maybe it is?
It is a ceramic tube painted black marked with 6.

I have been observing the crystal OSC frequency on the frequency meter 
over the past three weeks; for random periods of time.  The Crystal 
Reference Oscillator starts high 1000.220KHz. As the unit warms up after 
1 hour + 40Hz, after  2 hours the Crystal Oscillator comes down to 
1000KHz  +20 -6 Hz .

The Crystal Osc is a critical component; Dial Readings were based on the 
Crystal Calibration points.  If  Crystal OSC was bouncing up and down 
+/- 30Hz
that could lead to a 150Hz error or more on the high band.  It does not 
make sense that the 6pF is not a temperature compensating capacitor.  
Note: If this was SOP back in the DAY, WWII, I would have kept the freq 
meters running hot 24/7; and that is a lot of batteries.

If I were to replace the 6pF temperature compensating capacitor on the 
1000KHz crystal reference Oscillator with what would I replace it dear 
Lizor, with what?  What I think  need is a CAP that looses capacitance 
as the unit warms up to temperature.  If there is such a beast:
  How to correctly "document" the change in frequency over time and 
temperature.
  How to specify and select a capacitor that will stabilize the crystal Osc.

Any help and or direction greatly appreciated.


Thanks
Hutch