[time-nuts] Old Crystal.

[Bernd Neubig]

Hi,
 Sorry for the late  answer.  I was too busy to provide my suggestions for
the measurement of those crystals.
Using a network analyser, in this case you do not necessary need a
PI-network with 12.5 Ohm impedance at either side of the crystal port.
That PI-network was "invented" to "match" the typical resonance resistance
of Normal crystals which is in geometrical average in the range of about 25
Ohm. You crystal may have a higher R1, so inserting it in series between tow
10 dB attenuation pads would be appropriate to isolate it from the cable. It
will show 100 Ohm to the crystal.
The easiest test procedure (after calibration) is as follow:
1. Make a "first order" calibration by inserting a short in place of the
crystal and note the output amplitude (Vo) 2. Set the network analyser to
zero phase (if it is a scalar NWA: set it at maximum amplitude, this is
sufficiently accurate at 1 MHz). Note the frequeny fs and the amplitude (Vx)

     Frequency setting either manually or by slowly sweeping (it is slow
enough, if the zoomed resonance curve of the amplitude is symmetrically
bell-shaped 3. Note the amplitude at this point. From the voltage divider
formula you can derive the resistance as:
    R1 = RT*(Vo/Vx - 1)  with RT = 100 Ohm 4. Tune the frequency to the left
till the +45° point (scaler NWA: left 3 dB-point), note the frequency f1 5.
Tune the frequency to the right till the -45° point (scaler NWA: right 3
dB-point), note the frequency f2 6. From the frequency difference between 5
and 4 calculate the loaded QL  = fs/(f2-f1) 7. Calculate L1 = QL*(R1+100
Ohm)/(2*PI*fs) 8. Calculate C1 accordingly C1 = 1/(QL*(R1+100)*2*PI*fs) 9.
Measure C0 with a normal RLC tester 10. You got it

Regarding your idea to let the crystal glow: Cancel this idea !!!
a) it (the plasma discharge) will only work, if the crystal enclosure is
filled with Argon or similar. But most probably it is "filled" with vacuum
b) you need to drive the crystal with a very high drive level, which is
sufficient to energize the ions. This will destroy your crystal finally.

Enjoy

Bernd
DK1AG

----- Dan Kemppainen wrote-----

Hi All,

Many thanks to all who replied. I've beep picking my way through the
suggestion, videos, and other information.
The next steps will be to try to measure some of the crystal parameters with
the stuff I have laying around the lab. The supplied information will keep
me working on this for a while.
I did find one ebay seller who managed to make these tubes glow blue! 
Not sure how much voltage or what frequency it was getting hit with, but it
appears to be arcing in/on/through the crystal. Hopefully the ones I have
weren't mistreated this way!