[time-nuts] 5071A Cs Oven

Brian, WA1ZMS wa1zms at att.net
Thu Oct 4 20:22:45 UTC 2012


Rick can correct me on this...
but my understanding is that it is
almost never a case of running out
of Cs from the oven, but that the
dynodes of the electron multiplier
become covered in used Cs and so
the ultimate SNR and effective beam
current falls to a point where there is
no dependable beam current left to
do much with.

The tube that I sent to Paul, he was
able to get some more current by
running the Cs oven at a higher temp
and as such is vaporizing off LOTS of
Cs and can get a tiny bit of beam
current to work with. But it is a down
hill slide, since to keep the beam
current up with a "dirty" E-mult, over
time you need to keep running up the
Cs oven temp to the point where you
may just run out of Cs....or.... get an
E-mult that is so covered with used
Cs that there is no beam current to
work with. You can always try and
run up the E-mult voltage as well, but
you then run the risk of arcing in the
E-mult and an issue of burning up
the resistor divider stack that I believe
is part of the E-mult.

I can see it now...... an end-of-life Cs
tube that needs 35kV on the E-mult
to get any beam current to work with! 
: -)


-Brian, WA1ZMS

On Oct 4, 2012, at 3:41 PM, paul swed <paulswedb at gmail.com> wrote:

> Rick
> Well I have the old 5060 and 61 tubes and indeed they run out O gas.
> I am using a 5060 tube in a 5061 and the Frankenstein works though it has
> only a few Cs. But heck it all locks after 48 hours.
> So someone said with humor lets buy some 5071 tubes for a couple hundred
> each.
> Guess I could have some fun getting that into the 5061. Suspect that would
> be the bride of Frankenstein then.
> Thanks for sharing the insights and experience.
> Paul
> WB8TSL
> 
> On Thu, Oct 4, 2012 at 3:21 PM, Richard (Rick) Karlquist <
> richard at karlquist.com> wrote:
> 
>> 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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