[time-nuts] New Guy, has HP 5061A with DATUM 7105A tube seeks advice

John Miles john at miles.io
Thu Nov 6 18:41:18 EST 2014

There's a good chance you can get it working but not necessarily with the built-in ion pump supply.  In my experience, if it doesn't pump down within a day or two, it never will.  No point waiting multiple days or weeks.  The manual talks about how to connect an external HV power supply, and I wouldn't bother waiting longer than 24 hours to resort to that. 

The first time you switch the unit on, outgassing from either the ionizer or Cs oven (I'm not sure which) will cause the ion pump current to rise again and trigger a shutdown cycle almost immediately.  Initially it will take several minutes to recycle, at which point it will shut off again for a few more minutes.  Over time the duty cycle will improve until the unit can stay on indefinitely.  Meanwhile, though, the ionizer and oven filaments are taking a beating, as if you were manually toggling a light switch on and off.  On one tube I brought back to life, the ionizer filament failed quickly during this period.  The next time I have occasion to mess with one of these things, I think I'll use a variable power supply to determine which heat source is responsible for the outgassing cycles, and ramp it up slowly by hand to avoid stressing it.  This may seem a bit convoluted for your first experience with a cesium standard, and it may not even be helpful, but I don't see how the factory-specified power cycling process could be good for the tube.

If you get the tube working, you should use a counter or Lissajous display with a GPS or rubidium standard to preset it to the correct resonance peak frequency for lockup.  The tube will probably be pretty noisy at first.  If it also has weak beam current, which is common, it will be very difficult to find the right peak without cheating.

http://www.artekmanuals.com has a nice scan of the manual if you can't find a clean copy online.  You will need to become familiar with the manual sooner or later. 

-- john, KE5FX
Miles Design LLC

> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of paul swed
> Sent: Thursday, November 06, 2014 3:06 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] New Guy, has HP 5061A with DATUM 7105A tube seeks
> advice
> Yes follow the manual. You can't really hurt it.
> The first position is the pump position and you leave the switch there.
> Not much else is really running. Ovens warm and such. Turn the meter to ion
> pump and watch. Most likely it may go off scale to the right.
> Regards
> Paul

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