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

J. Forster jfor at quik.com
Sun Sep 6 17:04:35 UTC 2009

Cesium is pretty reactive and could likely be stripped off chemically and
the CBT tube cleaned.

People can make simple triodes at home (with a lot of stuff). There were
guys 'rebuilding' CRTs in the late 50s at home. However a CBT or other
things with electron multipliers are FAR from a simple triode. You not
only need exquisite vacuum technique, but also to be able to activate the
electron multiplier. These are non-trivial things to do, even for large,
expert companies. I was told by a guy at Varian that they typically did
three tube starts for every one delivered on image intensifiers, which
have MCP multipliers.

This is part of the reason I've never bought a used Cs standard. Most
likely it's a $$$ doorstop, and always will be.



> 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
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