[time-nuts] So what’s inside that Cs Beam Tube anyway?

Tom Van Baak tvb at LeapSecond.com
Wed Nov 2 13:23:39 EDT 2016

Hi Rick,

That's consistent with what I've seen and heard as well. Most of the 5061B / 5071A on eBay with dead tubes are opt 001 (high-performance) tubes. The surplus units with standard performance tubes are more likely to power up and lock. And if they don't, it's probably something simple rather than a dead Cs tube.

I've also heard that the choice of high- vs std-performance is made *after* the tube is built. The difference would be in things like the oven temp and detector gain, both of which are controlled outside the tube. My first hint of this was in a paper by Carroll Alley...

You know the famous 1971 Hafele-Keating experiment with four 5061 cesium clocks flying around the world. Several years later, a more precise measurement was made by Carroll Alley using better clocks. What I read is that he got Len Cutler to hack the 5061A so that its beam current would be higher, thereby improving performance for the duration of the experiment. Same tube, just different operating parameters.

See page 3 of:

For newcomers to the group, a good introduction to hp and flying clocks is here, along with copies of several HPJ articles:



----- Original Message ----- 
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Wednesday, November 02, 2016 7:53 AM
Subject: Re: [time-nuts] So what’s inside that Cs Beam Tube anyway?

> This has probably been covered here before, but, at least going
> to the 5071A, now 25 years ago!, all CBT's, whether high
> performance or not, have the same amount of cesium inside.
> This means that the standard performance (never call it
> "low" performance) CBT has enough cesium to last 30 years!
> Thus for those tubes, we can rule out cesium replenishment
> even if it were possible.
> Rick

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