[time-nuts] 5071A Cs Oven

tcurlee@sbcglobal.net tcurlee at sbcglobal.net
Thu Oct 4 15:53:47 EDT 2012


I've read that the 5071A has an almost indefinite tube life.  However, the 'high stability' option only has a 9 year life.  What happens after 9 years?  The tube stops working, or it degrades to the normal tube performance?

Tom  WB6UZZ
Sent from my HTC Inspire™ 4G on AT&T

----- Reply message -----
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: "Tom Van Baak" <tvb at LeapSecond.com>, "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Subject: [time-nuts] 5071A Cs Oven
Date: Thu, Oct 4, 2012 12:21 pm


These ideas are "interesting".  AFAIK, there is very little
chance of running out of Cs in many years, long past the
time when something else in the tube will have reached its
end of life.  Where did this idea come from?  Certainly, not
anyone working at HP, Agilent or Symmetricom.  A LONG time
ago, if you bought a high performance 5061, the increased
Cs beam flow might have been an issue, but the amount of Cs
shipped with the tube was increased before the 5071A
such that running out of Cs is no longer an issue.

If you turn off the Cs, you simply have a 10811 to connect
to your GPS.  Except this 10811 has 10X the EFC range vs
a stock 10811.  Again, this doesn't make a whole lot of sense,
IMHO.

BTW, another "interesting" idea is degaussing the CBT.  According
to Len Cutler, this is completely unnecessary in the 5071A.  As
anyone who knew Len can attest, if he thought something was
good enough and didn't need to be improved, you could be
sure about that.  For example, Len wanted us to use tantalum
filter capacitors for energy storage in the power supply.
Fortunately, we talked him out of that (actually the $100+
cost helped to convince him).

Due to customer demand (the customer is always right :-) the Santa
Clara Division eventually released a degausser.  One of the reasons why
this is not necessary in the 5071A is the Zeeman line measurement
of the magnetic C field.  The 5061 was open loop.  So again there
may have been a grain of truth behind the folklore.

Rick Karlquist N6RK
Member of the 5071A design team

On 10/4/2012 9:45 AM, Tom Van Baak wrote:
> Bob,
>
> Right, not good. There should be a fault message associated with it. Check the internal log.
>
> OTOH, to conserve cesium, I've heard that some people run 5071A in standby mode most of the time and only turn on the cesium for a fraction of an hour a day or a week (to recal the quartz). Running in this standby mode is also advisable if one wants the best short-term performance out of a 5071A, without the loop noise. In this respect it's just like a GPSDO - you get the best short-term performance if you turn off disciplining.
>
> /tvb
>
>> Hi
>>
>> Is "Cs oven: 0.0V" a good thing on a 5071A?
>>
>> I suspect not, since either it or GPS is off frequency.
>>
>> Bob
>
>
>
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