[time-nuts] 4 KV Power Supply Recommendations Update

[J. L. Trantham]

Just an  update on the status of the 5061A.  I started this thread on
January 17.  

When first turned on, it pegged the Ion Pump I meter and, at glacial speed,
seemed to be 'pumping down', as judged by measurements of voltage on pin 3
of the A18 +3500 VDC power supply.  I finally got tired of waiting and
obtained an Electrophoresis Power Supply, an E-C Apparatus EC600, that does
0-4000 V, 0-200 W, and 0-200 mA with any one of the three limiting as
selected (thanks to Tom Frank for this suggestion, does anyone have a
schematic for this unit?).  

After several weeks, it finally pumped down to the point that the internal
power supply would allow the CS Oven to turn on but then the Ion Pump I
would peg and take forever to pump down again.  After a few weeks of this
along with further 'pumping', I decided to modify the internal power supply
to allow the supply to 'cut off' the CS Oven at 80 uA instead of the
designed 40 uA by adding a 56K resistor across R6, the 75K resistor in the
A18 +3500 VDC power supply.  

This allowed the CS Oven to come on, then the Ion Pump I meter indication
would go up to the mid 40's, the  CS Oven would turn off, then the pump
would pump down, and repeat the cycle.  It now rests at around 30 uA on the
Ion Pump I and all meter indications are now normal with the 'turn on' value
on the Ion Pump I meter indication at around 36.  The Continuous Operation
light now comes on and, seemingly, it is working.

However, I don't think it is, at least not yet.  

I have the 5 MHz adjusted slightly high (about 5 mHz), as compared to my
GPSDO, and the control voltage slowly increases, the frequency slowly
decreases, passing through the GPSDO frequency and then the EFC voltage
continues to increase, driving the frequency progressively lower.  However,
it does not appear to 'lock' though I have not given it hours to show that.
My other CS units appear to 'lock' almost immediately once the Continuous
Operation light comes on.

It is behaving as if the 'Loop' is not closed even though it appears to be
able to make the comparison of the 5 MHz to the CS, adjust the frequency of
the 5 MHz in the appropriate direction, but then fails to 'lock'.

In order to get the 2nd Harmonic indication reasonable, I had to turn up the
Loop Gain and put the A7 in 'High' gain.  I am suspicious that I have other
'adjustments' to make but have not had time to pursue this in detail.

So, it appears that I have more work to do.  However, at least as far as the
Ion Pump goes, I think I have made progress.

Thanks to all for the suggestions/discussion thus far and any further
suggestions would be appreciated.

Joe