[time-nuts] 5071A Cs Oven

[Tom Van Baak]

Hi Rick,

What I've read or heard is that high-perf 5071 tubes last about 7 years (and then run out of cesium). However, the standard-perf tubes last much longer, maybe 20 years or more (and eventually fail for reasons other than ovens). But there have been different generations of tubes so I'm not sure if these numbers apply, say, to what Bob has.

You may be in a much better position than I to confirm any of this. There have been some papers on the subject. One I remember is:
http://tycho.usno.navy.mil/ptti/1997/Vol%2029_06.pdf

/tvb

----- Original 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>
Sent: Thursday, October 04, 2012 12:21 PM
Subject: Re: [time-nuts] 5071A Cs Oven


> 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