[time-nuts] Need some wisdom from the cesium beam tube gurus out there

Bob Camp kb8tq at n1k.org
Wed Nov 9 19:13:57 EST 2016


I would bet that they started as you have with a low oven setting and cranked
it up based on stability data.  Once they got to that point, add a bit to have enough
margin on the tube for it to last the rated life.  

Since there are multiple quantum “modes” the beam can get into, there may have been a bit of 
sweeping involved to keep this separated from that. If so, I suspect that the sweep 
procedure is long lost. You are pretty much stuck with the stability check / tweak / stability
check approach. 


> On Nov 9, 2016, at 7:02 PM, Skip Withrow <skip.withrow at gmail.com> wrote:
> Hello Time-Nuts,
> I have been checking out some cesium beam tubes lately and have run into an
> interesting one.  The tube is a standard HP 05061-6077 unit.  There are two
> labels on these tubes, one at the end that has a serial number, and the
> other large label on the side that has the operating information (and the
> serial number).  Problem with this tube is the large label is completely
> BLANK.  It appears that there was never any information on this label.  The
> source that it came from was pretty closely connected to HP, so it could be
> a tube that escaped before testing/characterization.
> The nice thing is that it works!  Using some random nominal resistors for
> the oven temperature I get good beam current.  Changing the electron
> multiplier voltage also dramatically changes the beam current.  I see the 3
> peaks around the on-frequency point quite nicely.
> So, the question is - how do I determine the operating point of the tube
> with no data?  I could fire up a known tube and set the beam current for
> the same value, but how would the oven temperature vs. electron multiplier
> voltage be resolved.  I would think that a lower oven temp and higher EM
> voltage would give the same beam current as a higher oven temp and lower EM
> voltage.
> I'm sure the HP did not do any characterization of the tube until it was
> all buttoned up.  So how did they determine the temperature of the oven?
> Just from the value of the internal thermistor?
> I suspect the answer is what kind of S/N ratio do I want?  If that is the
> case then I would be tempted to run at the lowest oven temp and highest EM
> voltage that gave me a usable signal - for the sake of tube life.
> Any thoughts?
> Thanks,
> Skip Withrow
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