[time-nuts] Rubidium cell or lamp rejuvenation. WAS-HP 5065A owners, a question!

[JF PICARD]

 Observed on 3 R&S XSR, on 10 5065A decommissioned together after 10...20 years of service (blue ones with Patek clock, green, black and green...with 10811A and digital clock...) --they were replaced by a GPS based synchronisation network--. plus some 5065A got here and there. The lamp assy I sold last year had the same problem. The HP specs were met in 50% of the units but there was Rb deposits (small irregular spots) in the lamps.
It is the main cause of the XSR failure and the lamp is field replacable (metal threaded base)     On Saturday, October 26, 2019, 11:01:06 PM GMT+2, <cdelect at juno.com> wrote:  
 
 JF, Reference your statement:

"Sorry, but I don't agree with your first statement about the 5065A :
after long use, the rubidium plates on the inner envelope of the lamp
(like silver on a mirror) and years after years the Rb light and photo I
decreases."

After working on the 5065A for over 40 years and across the full range of
Serial numbers and ages of instruments (somewhere over 70 units) I have
only seen Rubidium plated on the inside of the bulb twice. All the other
lamps provided performance that met the HP specifications. The design of
the lamp assy causes the tip of the lamp to be cold compared to the bulb
causing the majority of the Rubidium to condense into the tip.

The two bulbs were in units where the lamp oven winding shorted and
"cooked" the lamp Assy.
Those two bulbs were recovered using a heat gun.
I suppose if the unit was stored for years in a very hot environment the
Rubidium could get out of the tip but as long as the lamps starts you can
just let it run for a week or so and it will condense back into the tip.

If a you have a bulb that exhibits the plating I would recommend that you
measure the lamp oven temperature to make sure it is not too hot. Also
the two nuts on the lamp assy. rod that protrudes out of the cover should
clamp the outer cover firmly between them. The outer cover is a heat sink
for the lamp assy. and maintains the Rubidium in the tip. Operating for
years without this clamping might cause what you saw.

Other units specifically the Efratom FRS were poorly designed and are
known for this problem.

Cheers,

Corby
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