[time-nuts] Source of Rubidium Lamp for Efratom FRK

Chuck Harris cfharris at erols.com
Fri Jul 31 15:02:40 EDT 2015

Hi Mike,

That bulb was sealed with an oxy-fuel torch at the melting
point of the glass.  It was then annealed, starting at a much
higher temperature than 150C before cooled slowly to avoid

Heat it uniformly with your hot air gun until it is no longer
black.  Reducethe heat slowly to allow it to cool... or, you
can toss it into a can full of white ashes from your fireplace.

Or, leave it be and wait until it really fails before fixing

-Chuck Harris

Mike Niven wrote:
> Thanks Bob and Chuck for the comments.  As Bob says, the lamp is easily
> replaceable (just unscrews) and the service manual gives the procedure.  Maybe I'm
> too worried about how long the lamp is likely to last but the lamp voltage was
> below the range stated in both the Efratom and Racal manuals.  The lamp itself
> certainly works but is a bit blackened.  I had hoped that Corby's procedure for
> rejuvenating lamps might do more than it did for this particular lamp - maybe I
> chickened out too early in the heating process, but I was monitoring the local
> temperature with a thermocouple at over 150C consistently.  Anyway, I have asked
> Sematron in the UK whether a replacement lamp can still be had.  If it is
> available at $300-500, it is really not economic as the whole Racal 9475 cost a
> lot less.  Mind you, I did put in a fair amount of work repairing both the Racal
> main unit and the FRK to get the system working.  So, probably the best way of
> getting a spare lamp is to try and pick up another whole FRK and hope that its
> lamp still has some life in it.  Anybody know whether the same lamp was fitted to
> other Efratom Rb sources?  This would widen the search somewhat.
> Mike

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