[time-nuts] time-nuts Digest, Vol 194, Issue 45 Low lamp voltage Rb

[Andre]

What about using a the hot-air gun technique to migrate the Rb from the walls of the lamp back to the well?

David

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at lists.febo.com] On Behalf Of Bob kb8tq
Sent: 28 September 2020 14:23
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Symmetricom XPRO rubidium

Hi

> On Sep 27, 2020, at 10:19 PM, Stewart Cobb <stewart.cobb at gmail.com> wrote:
>
> I have a Symmetricom* XPRO rubidium which appears to be reaching its end of
> life. The very sparse manual says that it sets a "service" flag when the
> lamp voltage reaches 600 mV. When I got it, that parameter was at about
> 540. Several months of continuous runtime later, it's down to about 510.  I
> assume this is a measure of light emitted by the lamp, but its label is
> "lamp voltage".
>
> I don't want to lose this Rb, because it seems to be the most stable
> reference in my lab (about 2x more stable with temperature than a PRS10, by
> eyeball).
>
> Questions for the hive mind:
>
> (1) Why and how is the lamp voltage falling?  What's the wear-out
> mechanism?

It?s looking at the photo detector on the physics package. The amount of
light getting to the photo detector is ?getting low?. Once it gets low enough,
the SNR degrades. At some point that gets bad enough for the device to
loose lock

Yes, essentially this is part of the problem. As others have said Rb adsorbs into the glass and "sticks" outside 
the pinch resulting in problems very similar to an EOL conventional discharge lamp.
In fact I tried to source a broken Rb module (Efratom) with the aim of repairing it using a blue 2W laser + 3 element
lens but never managed to get one but got a double oven 10 MHz OCXO instead.

About the only good thing with this method vs the hairdrier method is lasers are a *lot* easier to align and aim at 
just the active part.
Get it right and the voltage should improve especially on a no-lock unit to the point that it may then work at least
for a while. 

I obtained this M140 with the intention of using it for etching and other applications.


>
> (2) Is there any hope of repair? Will the heat gun trick for the LPRO work
> on the XPRO? Could I replace the XPRO lamp bulb with one from a young LPRO?

The devices are ?aligned? to match up with the bulb. The various tweaks to get that
done are never documented on the Telecom Rb?s. You might get lucky, you might
not.

Yes, make notes for *everything*.  Ideally try and take pictures at highest resolution possible to aid with
reassembly later.