[time-nuts] HP5061B Ion Current

Donald E. Pauly trojancowboy at gmail.com
Mon Mar 20 22:59:30 EDT 2017


I could not figure out why the A15 Ion Current monitor would not let
the cesium oven turn on with ion current under 25 uA.  At the time we
had no way of measuring the +3,500 ion pump supply.  We bought some
200 Meg resistors and made a crude HV meter to feed our 10 Meg Fluke
77.  The supply had sagged to 2000 Volts with that load.  This
prevented the ion pump current monitor from energizing the cesium

KB7APQ unsoldered the can on the 3,500 Volt supply with suggestions
from WB4BBP.  It is a horrible design and we studied it.  R4 is set at
the factory to produce 3,500 Volts with no load.  It runs at 704
pulses per second and sags badly with the slightest load.  This
prevents the ion pump from clearing the gas in the beam tube.  The pot
core transformer is plenty big that it appears that the supply can put
out 5 mA at 3,500 volts.  This allows it to replace the external
supply recommended by HP for gassy tubes.

It looks like that it can run at 10 kc with existing pot core
transformer.  The pulse width looks like it can be doubled as well.
This allows for a 30 to 1 increase in output power.  A small circuit
board will regulate the voltage as well as limit the current.

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