[time-nuts] Buying and using used Cesium Beam Standards

[Taka Kamiya]

I am a Time-Nut in training.  I am still learning.  So I can only contribute a small amount.
I have an old Cesium standard by FTS, model FTS4040A.  Amazingly, it still locks.  Amazingly, it's still holding stable.  So far, works every time and frequency is the same.  But a big question remains....  for how long?  The answer is, I'll know when it no longer locks.  In talking to professionals and TimeNuts, there is a way to extend life time a bit, and if you keep watching, it will show tell-tale sign of the tube about to quit, but there is no really big red light warning about its death.
Even when you don't use the box and is turned off, "the time clock" (I mean wearing out) slows but still is ticking.  All things sealed will leak very very slowly.  Everything contained will slowly be consumed.  Per manual, every 6 months, you must turn it on and let the vacuum pump do its thing, or otherwise you will end up with contaminated and compromised tube.  I understand newer machines has a stand-by mode where pump is running but the rest is not.  Mine does not have such feature.  Every time I need it, I turned it on and wait for few days, then use it for a bit then shut it down.  It's not as useful as you might think.
But as mine is still usable after 25 to 30 years and with original tube, I guess rarely used and well cared for standard can last.

I bought mine from a local dealer for a good price.  So if it quits, so be it.  Replacement tubes are $30K to $40K range.  There is no way I can afford it.  Getting one in second hand market, forget it, unless you luck out.  There is an individual on this mailing list whom in the past had a batch of it and helped out many, as I understand.  But still usable tubes just don't become available.  Personally, I have never seen it on eBay in few years I've been watching.  Just to show how "sad" the situation is, I bought a non-working HP5071A with high-performance tube for $50.  I just took it apart for parts.  This is a $70K equipment!  It's really worth only for parts.

I will be more than happy to answer any "don't know what to ask" question you may have.  If I know it, I'll help you out.  You can ask me anything without fear!  But chance of me knowing something is rare at this moment.
By the way....  if I am going to buy one in used market, it will either be from a local source or from someone on this mailing list.  It is a well known secret that most dealers on eBay who advertise "tested" mean turned it on and red light came on.  
--------------------------------------- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

    On Tuesday, March 10, 2020, 8:00:45 PM EDT, Forrest Christian (List Account) <lists at packetflux.com> wrote:  
 
 I noted Skip Winthrow's message about the listing of a Cesium standard on
eBay.

I've had some questions generally about these used standards for some time
now, figured this was a good time to ask them.

So let's assume I buy a used unit in working condition.  I get it here, it
works fine, and everything is up to spec.  Let's also assume that I really
only need it operational a week or two a couple of times a year during
periods I'm doing measurements that require the stability of the Cesium
standard.

What is the best way to improve the odds that this used gear is
working properly when I need it?  I'm asking primarily because I know that
the cesium tube itself wears out, and replacing the tube does not often
make financial sense.  I guess I'm asking is if the 'wearout clock' on the
tube stops if the unit is powered off and is on the shelf, or if there's
something else one does to extend the life of these units.

All of the other questions I have are probably more in the category of "I'm
not sure what questions to ask".  I've owned/used/fixed a fair bit of used
test equipment over the years, but this seems to be in an entirely
different category.  I've never had any experience with these at all, so if
anyone would like to pontificate with any wisdom or experience in the
basics of acquiring and using a Cesium standard I'd appreciate it.

-- 
- Forrest
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