[time-nuts] Need HP 5061A setup help

Skip Withrow skip.withrow at gmail.com
Fri Mar 17 11:37:46 EDT 2017

Hello Time-Nuts,

I have an HP 5061A (relatively new chassis) with a very old Cs tube
installed (working) and I’m trying to wrap my head around the set up and
calibration of this unit, and just hoping for some help.

As a little background, HP changed the Zeeman modulation frequency, C-field
intensity, and A1 synthesizer frequency at serial number prefix 1336A.  This
is detailed in CHANGE 20 (pages 7-9 and 7-10) Model 5061A Manual Changes in
the 5061A Manual, and covered in much more detail in HP Service Note
5061A-9 (document 05061-9061 6/80-02).

                                    OLD                            NEW

Zeeman frequency            42.82kHz                    53.53kHz

C-field                          61 milligauss                      76

Synth. Frequency            12,631,771.6 Hz            12,631,772.5 Hz

I can put the tube on frequency at the new synthesizer frequency by
changing the C-field current (closer to the old C-field value, by changing

1. The Zeeman modulation frequency is a complete mystery to me.  Is it
related to the value of the C-field that you are running?

2. If you are comparing the unit to GPS to calibrate it do you really care
what the Zeeman frequency is?  Adjust the C-field to put it on frequency
and call it a day?

I’m not sure if there was a physical change in the Cs tube as well.  But HP
mentions that the new values should have better stability.

3. Would I be better off changing the synthesizer frequency back to the old
value and adjusting the C-field (I would think lower) to put the unit on
frequency? My first thought is to leave well enough alone.

Thanks for any insight.

Skip Withrow

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