[time-nuts] Thoughts on Cs tube failure modes

[Corby Dawson]

John,

What you describe with the ion pump curent is normal if the tube has been
powerd off for a long time.

Th mainframe normally would turn the oven and ionizer filaments off when
the ion pump current pegged.

After minutes (can be quite a few minutes) the ion pump current will drop
as it pumps the surge of outgassing from the heated filaments.

The cycle repeats and can take a couple days on a stubborn tube.

You bypassed that circuit so I'm not sure how much gas you introduced.

If after a couple days the current is still pegged try connecting an
external high voltage supply of around +3000VDC that can provide at least
5ma. (turn unit off)

Let it run overnight and if the current comes down reconnect the internal
power supply and turn the mainframe back on.

You probably will see it peg again and the see the oven shut down (it
happens fast!), just leave it on and it should start cycling and
eventually the filaments will reach the oven set points and have
outgassed enough so that the protective circuit will not trip.

Then you can try to see if the rest of the tube has any life. (you may
have to reduce the oven set resistor to 130 ohms as well as reducing its
companion overtemp resistor. This is the value the Navy uses to get the
last bit of life out of the tube, don't do it if you can get the rated
beam current at the original value!)

If you email me I can give you my evening phone number if you need some
more info.

Corby Dawson
cdelect at juno.com




 
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