[time-nuts] Hp 5060A C-field

Tom Van Baak (lab) tvb at leapsecond.com
Fri Jan 3 13:13:06 EST 2014


Hi Paul,

About cesium clocks: hp 5060A and early versions of the hp 5061A needed to be able to keep *either* atomic time (true, accurate, stable, SI seconds) or astronomical time (inaccurate, unstable, slow, and gradually slowing, earth rotation time).

The larger C-field range allowed this user choice of time-scales. I have many examples of both clocks here. 

It appears most time & frequency labs converted to "atomic time" in the late 60's and 70's which is why all later 5061A, all 5061B, every 5071A, and all modern atomic/ion/optical clocks tick "atomic" seconds instead of the slightly larger and monthly / seasonally / climatically / geologically / gravitationally variable "earth" seconds. And why we have leap seconds.

In the past 50 years even die-hard astronomers have thrown in the towel and conceded that atomic time is a more stable time reference than earth rotation rate. In order to point modern, super-accurate telescopes they use a high-precision (sub-millisecond!) "DUT1" correction to convert physics-stable atomic time into engineering-accurate astronomical time; "close enough for government pointing work" as they say.

Now that we're well into the post-astronomical time age, the narrow C-field range is adequate. If you have a 5060 or older 5061 there is no harm in using resistors to restrict the C-field range.

/tvb (i5s)

> On Jan 3, 2014, at 7:51 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Corby
> Having a good time tinkering with the 5061. Did change the resistors for
> the cfield regulator so that its much close to the schematic and am
> experimenting with that.
> The system does seems to be able to be tuned through a stable position that
> reduces the drift to 2 min/10ns drift and the CS is slow compared to the
> 5065 RB set to loran C when its on the air.
> I do have a older synth div board. No thumbwheel switches. It appears to me
> to be jumpered at 8634. I think that may be wrong. The book says 2095 for
> atomic time.
> Appreciate your thoughts.
> Regards
> Paul
> 
> 
>> On Thu, Jan 2, 2014 at 4:52 PM, paul swed <paulswedb at gmail.com> wrote:
>> 
>> Corby
>> I pulled the a15 board and there are no resistors, just a short across
>> what would have been r19 and 21. So I suspect that there is to much current
>> actually. Further speculation is that when the pot is toward ground more
>> current flows from what I see in the schematic.
>> I may guess that more current equals lower frequency?
>> Regards
>> Paul.
>> 
>> 
>>> On Thu, Jan 2, 2014 at 4:22 PM, <cdelect at juno.com> wrote:
>>> 
>>> Paul the C-field current is the same for the 5061A and 5060A.
>>> 
>>> The 5060A C-field pot has LOTS more range than the later 5061A where they
>>> installed resistors on each side of the pot to reduce the range.
>>> 
>>> Corby
>>> 
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>> 
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