[time-nuts] Old Crystal.

[Ed Palmer]

On 2021-02-28 5:53 PM, Dan Kemppainen wrote:
> Hi All,
>
> I've picked up a couple of old crystals. Mostly because they look neat.
> They are 1Mhz, in a glass tube. The quartz is ~25mm dia, at about 1 mm
> thick. Was able to get them to oscillate using a Colpitts circuit. They
> will oscillate at 2.851Mhz (probably some strange mode)  if given the
> chance.
>
> I've been scouring my reference books here, and haven't had much luck
> finding any details on how one would even guess at the parameters of a
> quartz like this.
>
> There area few numbers on them, 33 stamped on the side, 1000 (KHz???) on
> the top, 87 on the top, and hand written 501 (probably a SN). Digging on
> line, I'd guess an AT cut based on thickness. I'm guessing the 33 is
> capacitance in pF. 87, might be year.
>
> If any of you have any suggestions on where to find information on how
> to get something like this to oscillate properly, guess at correct
> parameters, or even measure any of the parameters I would really
> appreciate it.
>
> I'm sure these are really nothing special, but it would be neat to give
> them a fighting chance to show what they can or can't do without
> breaking them!

Those are available from at least a couple of Ukrainian ebay sellers.  
Search for "1000 khz".  There's also one that comes complete with the 
oven assembly: https://www.ebay.ca/itm/254748662460 .  I picked up a few 
of the bare crystals to help me understand the oscillator circuit in my 
HP 104AR frequency reference.  I breadboarded a circuit that was similar 
to the 104AR (i.e. similar to the HP 103AR) and with a couple of circuit 
changes the crystal worked properly.  I changed the transistor from 
Germanium to Silicon and changed C105 from 30nf to 3nf.  Note that you 
*MUST* build the AGC circuit or you'll probably destroy the crystal by 
overdriving it.  Play with the base bias voltage to get the circuit to 
oscillate.

I used a Saunders 100HF meter to measure the crystal parameters, but I 
don't understand the results.  Cm = 16 ff and Lm = 1.6 H which are 
fine.  But Rs < 1 ohm??  Other crystals measured using the same 
technique gave me results in the tens or hundreds of ohms.  But all four 
of these crystals measured < 1 ohm.

I haven't done any temperature testing on them.

Ed