[time-nuts] HP 5071A Electron Multiplier of Cesium Beam Tube

Rick Karlquist richard at karlquist.com
Sun Sep 6 16:49:23 UTC 2009

weijiazhen at sina.com wrote:
> Hi all,
> I got an HP 5071A,but it did not work.I think the Electron Multiplier
> decay problem. I want to change Electron Multiplier of Cesium Beam Tube .
> where to buy the Electron Multiplier and how to replace it? Thanks.
> weijiazhen

If you are not a CBT production line:

"forget about it"

On the other hand, if you are a CBT production line:

also "forget about it"

Back when HP/Agilent made the tubes, they welded them shut, baked
them out, pulled a vacuum on them, and sealed them, but did NOT
break the glass ampule that held the cesium.  They then did various
tests on the CBT.  A fair percentage of them did not pass.  In
that case, they were sent to the machine shop and placed in a lathe.
Any expert machinist cut off the weld, which went around the tube,
without damaging the structure beyond repair.  Of course, this
caused the high vacuum inside the CBT to escape :-)  The CBT's
were then sent back to the CBT line for rework, etc.  It is important
to understand that this was done with the cesium safely contained
in the ampule.  If a CBT passed the initial tests, a firing pin was
used to break the ampule, using a magnet to activate it, IIRC.

According to the CBT people, it was not practical to rework CBT's
that had the cesium released, let alone to rework used CBT's.
Used CBT's are even worse because everything is "cesiated".

Rick Karlquist N6RK

More information about the time-nuts mailing list