[time-nuts] High Voltage lead on HP Cesium Tubes

[J. L. Trantham]

Has anyone ever replaced a high voltage lead on an HP Cesium tube?

I have a 5061A that required prolonged pumping at +6000 VDC to get the Ion
Pump current to go down enough to allow the unit to turn on the CS Oven but
then would slowly increase to the point that it would again not let the CS
Oven turn on.  

At +6000 VDC, the current would be about 1400 uA but only about 30 uA at
+4000 VDC.  It got me to thinking that there was some sort of HV breakdown
going on.  On inspecting the tube and HV lead more carefully, I found the
+3500 VDC lead cracked and considerable 'soot' on the silicone 'cap' on the
tube where the red HV lead entered the tube.  I removed the connector,
cleaned the wire and silicone cap, separated the silicone from the lead and
slid some heat shrink tubing over the wire and into the silicone cap.  I
used the heat gun to shrink it in place then placed another layer on this.

Now, the tube seems to work OK (at least observing it for about 48 hours)
with the Ion Pump I stable at about 6 and with no increase, a distinct
change and improvement from before.

Perhaps I should be satisfied with what I have got but I was wondering what
is under the silicone caps and how to go about removing them to replace the
+3500 VDC and -2500 VDC leads.

Does anyone have any experience with this?

Thanks in advance.

Joe