[time-nuts] HP5065a cfield issue

[Bob kb8tq]

Hi

Well that puts it at 5/3 = 1.3 ppb low. The C field *should*adjust over a
2 ppb-ish range. Assuming you were near center, that puts the shift in the
“couple of ppb” range. Very much the sort of thing the synth could do. 

Bob

> On Dec 1, 2020, at 9:44 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Bob
> I did not see your response before responding to Poul.
> This morning I did flip those switches and agree that I may have something
> going on in the synthesizer. The offset that showed up is a drift of 5ns in
> 3 seconds and its running slow.
> I do have the offsets from past measurements. Will have to look them up.
> Regards
> Paul.
> 
> On Tue, Dec 1, 2020 at 8:51 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> The C field coil resistance is low enough that you have something in the
>> vicinity
>> of 10mv across it. If you want to check the C field regulator, I’d just
>> pop a wire and
>> put a meter in series with the coil.
>> 
>> My bet: your synthesizer has slipped a bit somewhere. I’d check it’s output
>> against the table in the manual to make sure it’s still on frequency
>> before I dove
>> into the C field. If it’s off, the switches would be my first target.
>> Rotate them a bit
>> to wipe off the contacts and see if the frequency is correct when you
>> reset them
>> to the original position.
>> 
>> If none of that works, I’d be happy to give your 5065 a new home :)
>> 
>> Bob
>> 
>>> On Nov 30, 2020, at 6:57 PM, paul swed <paulswedb at gmail.com> wrote:
>>> 
>>> Hello to the group.
>>> Was time for the quarterly Cesium and RB checks in an effort to support
>> our
>>> local power company.
>>> I discovered that there is an issue with the HP5065a Rubidium reference.
>>> 
>>> The frequency has slowed and the cfield pot can not make up for the jump.
>>> Normally a few small tick marks are ever needed. I used 3 large marks and
>>> ran out of pot. Its at 9.9. Was at 6.14. The frequency does increate with
>>> the cfield adjustment. I am assuming perhaps something has happened in
>> the
>>> cfield regulator.
>>> At least the front panel meter is indicating the +20V supply is normal.
>>> But my question is this. The schematic indicate very little current
>> travels
>>> through the cfield coil. Guessing far less than 3 ma. by adding up
>>> resistors. What I do not know yet is what is the resistance of the cfield
>>> coil? I may find that I simply have dirty contacts on the A15 regulator
>>> card.
>>> Its possible there are other things wrong but all front panel meter
>>> readings look the same as they have been for years.
>>> 
>>> Thoughts?
>>> Thank you in advance.
>>> Paul
>>> WB8TSL
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