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

[paul swed]

Forrest as Taka says pump it down. But I can add a bit to that. Old cesiums
seem to have trouble pumping down. Say you get it to pump down but it took
a week or two. In 30 days does it pump down quick or take a week. To me
that establishes how often the tube needs to be pumped down. I typically do
that about every 90 days. But I have a mix of old cesiums.
Like you I turn them on for critical measurements or when eLORAN is on for
solid comparison. The eLORAN signal is using a HP 5071.
GPS has seriously made me lazy by the way and saves a lot of money on power
these days.
A warmed up cesium is about 40 watts. Four of them is more. :-)
The other great things about time-nuts is there really is a lot of good
knowledge on the care and feeding of the old 5061s.
Regards
Paul.
WB8TSL

On Tue, Mar 10, 2020 at 8:34 PM Taka Kamiya via time-nuts <
time-nuts at lists.febo.com> wrote:

> 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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