[time-nuts] HP 10544A Repair

Bob Camp kb8tq at n1k.org
Mon Feb 29 07:39:58 EST 2016


Hi

An SC cut OCXO stabilizes a bit faster from the temperature steps. The procedure Rick described
is indeed the right way to do it for an SC. It takes less time and is reasonably accurate. For a super
duper job you might come back a day later, but the pot its self (backlash etc) will probably limit you. 
With another parameter to read out (pot voltage maybe) as you do the set, things could get more
precise. 

AT’s and BT’s are not quite as forgiving as an SC. The process I outlined is a bit of an exaggeration, but
it gives you a good idea of what you are in for. Doubly so if this is your first attempt to do a blind hole
adjust on a pot to 1/32 turn ….(engage without moving it, back off for the backlash, return, past 
previous point, stop at 1/32 .. so much fun).

Bob


> On Feb 28, 2016, at 11:19 PM, Glenn Little WB4UIV <glennmaillist at bellsouth.net> wrote:
> 
> While in the navy, I had to repair a hp cesium standard.
> The control circuit had the oscillator slewed to one limit, I do not remember whether high or low.
> We had no spare parts to support this standard.
> The only option was to run the standard open loop.
> Over a period of two hours, I had the standard off for no more than 15 minutes total.
> To get the standard back on frequency, I had to compare this standard to the other standard using an oscilloscope to produce a Lissajous pattern.
> I set the oscillator on frequency by stopping the rotation.
> I checked it again in 6 hours and the pattern was fastly rotating.
> I reset the frequency and checked it at 6 hour intervals.
> It took two weeks for the oscillator to thermally stabilize after being off only 15 minutes.
> Be prepared to have to wait to get the oscillator thermally stabilized.
> 
> I am not positive that this was a 10544A, but, it was a similar ovenized precision oscillator.
> 
> 
> YMMV
> 
> 73
> Glenn
> WB4UIV
> 
> 
> On 2/28/2016 8:10 PM, Bob Camp wrote:
>> Hi
>> 
>> Except ….
>> 
>> The big steps give you more “thermal shock” on a BT and that slows things down.
>> 
>> Bob
>> 
>>> On Feb 28, 2016, at 7:28 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
>>> 
>>> 
>>> 
>>> On 2/28/2016 7:01 AM, Bob Camp wrote:
>>>> Hi
>>>> 
>>>> It’s not an electrical issue as much as a heat issue ….
>>>> 
>>>> Before you start, consider that you will be doing something like:
>>>> 
>>>> Move trimmer 1 turn CW
>>>> Wait 10 minutes
>>>> read frequency
>>>> Move trimmer 1 turn CW
>>>> wait / read
>>>> Move trimer 1/2 turn CCW
>>>> wait / read
>>>> Move trimmer 1/4 turn CW
>>>> wait / read
>>>> Move trimmer 1/8 turn CCW
>>>> wait / read
>>>> Move trimmer 1/16 turn CW
>>>> wait / read
>>>> Move trimmer 1/32 turn CW
>>>> wait / read
>>>> 
>>>> That is indeed an ideal version. You likely will do multiple steps at each of the stages rather
>>>> than get it right the first time. The part needs to be warmed up for a few days before you
>>>> can get to the 1/32 turn level. You also need a good standard to compare to.
>>>> 
>>>> Bob
>>>> 
>>> 
>>> Instead of that, start with the pot at max temp, and have the counter make measurements at, say, 1 second intervals as the oven warms up.
>>> You can tell by looking at the plot what the peak frequency is.  Now
>>> that you know the peak frequency you are shooting for, it will take
>>> a lot less trial and error to find the oven setting that produces it.
>>> 
>>> Rick
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> 
> -- 
> -----------------------------------------------------------------------
> Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
> Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
> QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
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> of the Amateur that holds the license"
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