[time-nuts] 5071A Cs Oven

Brian, WA1ZMS wa1zms at att.net
Thu Oct 4 22:56:25 UTC 2012


Paul-
Same here! :- )
The best way is to find a REALLY dead
tube and cut it open and "see" if the EM
first and second dynodes are clean, or
covered in a film of Cs. Short of heating
the dynode to vaporize off the Cs and
let the ion pump collect it, I think it
becomes a giant physics project.

One really crazy idea is to cut the steel
casing open, but leave the glass seal
intact. If that's even possible. Then.....
you could use RF inductive heating like
what is used when you make a classic
vaccum tube, to heat the elements
inside and vaporize the occluded (sp?)
gases from the elements and let the
getter material or the ion pump gather
the crud up.

My only guess is if that was a real
practical way of adding life back to
a Cs tube, that HP or somebody would
have been doing it in the 1970's when
vaccum tubes were still in mass
production and the effort would have
paid off.

In light of the fact that Symetricom only
wants a paultry $18k for a new CBT...
and now with GPS birds running Rb's
rather than Cs....AND.... you can get a
CSAC for $1500 new, the demand for
Cs tubes has but a limited market.

Now if I could convince my XYL that
I must spend $250k on an H-MASER
then I'd be in Time-Nut's Nerdvana!

-Brian, WA1ZMS

On Oct 4, 2012, at 4:59 PM, paul swed <paulswedb at gmail.com> wrote:

> Brian
> Funny you mention the dirty emult. At the time I was wondering and if there
> was any insane way to get the Cs off the e multiplier. HV to ground or
> something to migrate them.
> Hold upside down and shake hard. ;-)
> Regards
> Paul
> 
> On Thu, Oct 4, 2012 at 4:22 PM, Brian, WA1ZMS <wa1zms at att.net> wrote:
> 
>> 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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