[time-nuts] Datum 4065A Cs Tube Response

Magnus Danielson magnus at rubidium.dyndns.org
Mon May 5 18:22:35 UTC 2014

Hi Ed,

On 05/05/2014 07:45 AM, Ed Palmer wrote:
> I'm playing with my first Cs standard.  It's a Datum 4065A which appears
> to have a dead STEL-1173 synthesizer.  Before I put too much effort into
> replacing that, I thought I'd check the tube and see if it has any life
> left.  I've attached a chart showing the response of the central peak.

Looks nice.

I had the same issue with one of my cesiums, so I got lucky and got a 
STEL 1173 in 44 pin PLCC, replaced it and then it worked.

What happens is that the output drivers for the STEL 1173 dies one after 
another and eventually you end up noise.

> My methodology was similar to TVB's as shown here:
> http://www.leapsecond.com/pages/cspeak except that I measured the tube
> output directly with a digital voltmeter.  The system is reporting
> wildly varying levels for the beam current so I didn't want to use any
> of it's circuitry.

I found the suitable test-point and multiplied with the network 
analyzers output signal as replacing the 12.6 MHz signal, and then the 
output of that into the network analyzer and that way got a nice way of 
checking the tube.

> Does this look like a usable tube?  Healthy or on it's last legs? What
> response levels are typical for a Datum 7504A tube?  I see that these
> levels are somewhat lower than those shown on leapsecond for the 5061A
> tube, but that could just be the specifics of the measurement.

Well, looks worth trying replaing the STEL for.

Good luck and hope it works out for you!


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