[R-390] Wanted: 14mHz Crystal

[Bob kb8tq]

Hi

The delta frequency from ovens off is about 25 to 35 ppm. At 14 MHz that puts you about 500 Hz off. 

The “tolerance” on many of these low cost crystals is around 200 to 1,000 ppm. That’s a much bigger shift.

The load capacitance of the circuit vs the test load for the cheap crystal also matters. That can easily
put you another 400 ppm off frequency. 

There are a mind boggling multitude of these crystals. There is no “one single way” to look at them.

Fun!!!

Bob

> On Jul 5, 2026, at 9:55 AM, Francesco Ledda <k5urg at yahoo.com> wrote:
> 
> It probably doesn’t matter, as the turning point of the original R-390’s crystal is at the operating point of the ovens, and most owners keep the ovens turned off.
> 
> Best, Francesco K5URG
> 
> 
> Sent from my iPad
> 
>> On Jul 5, 2026, at 07:00, Bob kb8tq via R-390 <r-390 at mailman.qth.net> wrote:
>> 
>> Hi
>> 
>> A generic crystal from Digikey is not going to have the same temperature characteristic
>> as the original. The radio may drift a bit as a result.
>> 
>> it also may not have the ability to tune to the correct frequency.
>> 
>> For < $1, try it and see is not that bad an idea. Just be willing to check things out a bit
>> and possibly buy a couple candidates.
>> 
>> Bob
>> 
>>> On Jul 4, 2026, at 6:42 PM, Fred Moore via R-390 <r-390 at mailman.qth.net> wrote:
>>> 
>>> Bill (and others needing crystals),
>>> 
>>> 1.  I do have one from an R-390 (not A) oscillator unit.  Fair Radio was
>>> selling these for $20 near their end, plus shipping.  Payment by check.
>>> 
>>> 2.  But other crystals will fail from time to time.  So I went on
>>> Digikey.com... They have a bunch of crystals, mostly SMD types.  These could
>>> be put inside the original holder.  Even MHz are pretty common there.  What
>>> about drive levels?  Is a tube osc too much drive for this little thing?
>>> There is a datasheet for it on this page.  So this approach might help others
>>> in the future.
>>> 
>>> Here is one by CTS for $0.72:
>>> https://www.digikey.com/en/products/detail/cts-frequency-controls/406C35B14M00000/604558
>>> 
>>> So this approach might help others in the future.
>>> 
>>> -Fred
>>> 
>>> ------ Original Message ------
>>> Received: Sat, 04 Jul 2026 05:22:44 PM GMT
>>> From: Bill Cotter via R-390 <r-390 at mailman.qth.net>
>>> To: r-390 at mailman.qth.net
>>> Subject: [R-390] Wanted:  14mHz Crystal
>>> 
>>> Happy July 4th!
>>> 
>>> Does anyone have a donor crystal bank with a 14mHz crystal they
>>> would be willing to part with? Please advise with price + shipping
>>> to my QTH (below).
>>> 
>>> Thanks es 73 Bill N4LG
>>> 
>>> 
>>> 
>>> 
>>> ------------------------------------------------------------
>>> Bill Cotter, N4LG              E-mail: n4lg at qx.net
>>> 173 Carolyn Lane               Cell: (859) 552-7481
>>> Nicholasville, KY 40356-9340 https://www.qrz.com/db/n4lg
>>> 
>>> ARCI #9878, QRPl #1646, QCWA #29393, FISTS #4535, NAQCC 7470
>>> ------------------------------------------------------------
>>> 
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