Hi

The temperature of the crystal is driven by the oven design. AT / SC / BT / IT
or whatever …. it is going to be over 80C. It’s not a function of the crystal. It
is what the physics of the oven force you to do. Inner oven must be hotter
than outer oven. Outer oven must be hotter than the maximum ambient of
50C.

Bob

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@gmail.com wrote:

Hi Paul,

As we have discussed a small eternity ago, the heat-up of the oscillator
gives a pretty good clue of what sits there. This is just from the fact
that the cold room temperature oscillator will shift very differently
from it's heated temperature by the oven and just observing which range
you can figure out what cut you most likely have.

I have a habbit to look at that heat-up and noted they where different.
Looking at charts for AT, BT, IT and SC cuts we could estimate frequency
offset for room temperature and those spoke to confirm. Naturally, this
was ovenized. TCXOs do not do the same thing as they are compensated,
and most generally AT cut as far as I know.

Cheers,
Magnus

On 2021-02-17 00:17, paul swed wrote:

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

Bob
That being said then this thing is way off in temp and I wonder if I can
even get it to any place close. That suggests disconnecting the oven
controller and manually controlling the heating element. The inner is 80
ohms nichrome and the outer 39 ohms. Inner is actually far easier to mess
with and to also add thermocouples and such to monitor.
If I understand this correctly as I drive the temperature up I think the
crystal will go lower in frequency. The oven heater is driven off the 15 V
supply and ground. But You would almost have to use the +15 to -15 to get
enough current I suspect. The last darn issue is why is the inner oven
meter reading in the normal range? That defies logic.
Quite the mystery/puzzle, just whats needed as the winter storms come
through.
Regards
Paul.

On Tue, Feb 16, 2021 at 9:11 PM Bob kb8tq kb8tq@n1k.org wrote:

Bob
I thought SC's were around a long time. (Not that I doubt you on that) This
thing should be the 1970s vintage from the one bit I have found on it.
Magnus always appreciate your comments. As I heat it up from room
temperature what exactly would I look for? Sort of the
temperature/frequency behaviors I see in various charts?
When cold the units sit 4Hz high. and when warm its currently .119 Hz high.
It used to go below by .6 Hz. Not sure what has changed.
Regards
Paul.

On Wed, Feb 17, 2021 at 9:31 AM Bob kb8tq kb8tq@n1k.org wrote:

Hi

SC cut:

1534592 https://ieeexplore.ieee.org/document/1534592

First really talked about in the early 1980’s and at that point an HP oddity.
At least in terms of actually being used in any sort of production product.
There are quite literally many hundreds of “known” crystal cuts that could
be used in an OCXO. Dig enough and the papers for this or that cut go back to
something that came before. Eventually you get to the 1920’s.

Based on knowing a number of the FE folks and having worked with some
of them, they had no interest in / role in the SC in the 1970’s. It takes a lot
of work to move a crystal cut from “known” to “production ready”. None of
it is very exciting, but those 100’s of man-years do have to be put in.

As an OCXO crystal, an SC with a turn at 40C would be a pretty terrible
choice, even if you could stabilize the the oven(s). An AT would be a much
better way to go.

Bob

See pages 20-29 in the Mar-1981 HPJ for the "new SC-cut" 10811 article(s):

https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-03.pdf

It talks about 10544A/C/B and 10811A/B in detail. It compares AT/BT/SC cuts.

Read especially "The SC Cut, a Brief Summary" on page 22.

/tvb

On 2/17/2021 6:38 AM, paul swed wrote:

Hi Tom,

On 2021-02-17 16:24, Tom Van Baak wrote:

Thanks for reminding us of this HPJ.

In here it is also noted that the 10544 is a BT cut, and this comes to
contrast that HP never come clean with which cut was used, as some have
said. Here we have some clear evidence.

Also note that it traces the SC-cut back to 1974, and that the same cut
also been called TTC and TS in early papers. It's interesting to note
that HP had double-angle cut machines since 1965, so the new cut did not
caused them a big challenge. Exactly which double-angle cut's they did
before SC remains to be found.

It is however interesting. They also refer to early papers in page 22
and 23.

Cheers,
Magnus