[time-nuts] AN/URQ13 reference AT cut crystal?

[Bob kb8tq]

Hi

If it was made before 1981 it pretty much certainly is *not* an SC. That’s
not to say it is an AT. A lot of crystal cuts got used in OCXO’s over the 
years. 

My guess, it broke, somebody took it apart and threw away the defective
crystal. It was replaced with a random unit from the junk box and the ovens
were (effectively) turned off. 

Bob

> On Feb 16, 2021, at 8:18 PM, paul swed <paulswedb at gmail.com> wrote:
> 
> After a bit of research I am wondering if this odd unit was actually an
> attempt at a AT cut crystal reference. The temperatures seem to line up.
> Its certainly an alpha or less product.
> It was stable at 43 F.
> Was thinking about disconnecting the oven and bringing the leads out to
> manually control the temp. With a quality external temp meter. Then see as
> the temperature is adjusted, does it follow an AT cut curve.
> As someone on the thread said "it maybe working as intended".
> Regards
> Paul
> WB8TSL
> 
> On Tue, Feb 16, 2021 at 6:17 PM paul swed <paulswedb at gmail.com> wrote:
> 
>> Hello to the group still working and decoding the AN/URQ-13 reference
>> oscillator. Bob had mentioned that the crystal should be at 85 C and thats
>> right for a SC cut crystal. Would there be any reason that this oscillator
>> is perhaps a AT cut crystal thats in the 30 C range. Just odd that the
>> front meter reads in the normal temperature range and the real
>> measurement is 40C. Makes no sense but they build AT cut crystals for some
>> reason.
>> Ehat about the smaller ovens like Piezo's. Pretty sure I can find many
>> details on the Morion oscillators like the MV200.
>> 
>> Other bits of details.
>> There are 2 discreet regulators that simply produce most likely a low
>> noise +/-8.5V. The Oven heaters seem to run on +15V and the divider analog
>> circuits need 13V min to work. But not 15V. That seems to cause some
>> distortion.
>> The other circuit on the board attached to the oscillator is a buffer amp.
>> It does have several meter resistors on it also.
>> 
>> Regards
>> Paul
>> 
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