[time-nuts] HP5061B Ion Current

cdelect at juno.com cdelect at juno.com
Tue Mar 21 13:29:58 EDT 2017

If you cannot get the ion current below 50ua or so after a week at 5kV
then you are out of luck.
Most likely you have resistive deposits on the ion pump insulator.
If you can get the tube to give a decent SN at those levels then you can
run with the alarm circuit bypassed.
I have run tubes a couple years this way (at <50ua) but if you let them
sit cold you will have to manually cycle the ovens at turn on until the
excess gas load is pumped.
If you have a bad ion pump supply when you open it up to repair it I
would suggest adding a 66K resistor across the 75K resistor. This will
increase the alarm trip up to about 40-45ua.
If it's the older one the oil capacitors will need changing as well as
the 200Meg resistor.
If the later one (in the 5061B) then the 47uf radial cap is open. both
these units are interchangeable.
One other trick is to use a spark discharge tester (miniature hand held
tesla coil used in the neon sign industry) to ZAP the ion pump lead.
This can blow out any whiskers that the ion pump has developed. You can
also (carefully) with the HV on, remove and replace the ion pump
connector a few times. Sometimes you will get a sharp discharge that
blows out the whisker. I have used both methods with good success.



More information about the time-nuts mailing list