[time-nuts] Old Crystal.

[Bob kb8tq]

Hi


> On Mar 1, 2021, at 12:52 AM, Ed Palmer <ed_palmer at sasktel.net> wrote:
> 
> 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.

That would give you a Q > 10M. While this would be a wonderful outcome,
it’s not likely to happen with a 1 MHz fundamental quartz crystal. 

Best guess: Your 100HF needs to be calibrated. Check the manual for details.

Bob

> 
> I haven't done any temperature testing on them.
> 
> Ed
> 
> 
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