[time-nuts] Re: Attempting to start HP5061A {External}

[Jim Muehlberg]

Hi Matt,

I just went through this when resurrecting a 5061A option 4 that was 
about to be scrapped (Horrors!).  My ion pump power supply was flakey, 
but after I fiddled with it, I got it to work.  I then saw the same 
behaviour.  Ultimately, I connected an external supply to the ion pump 
and left it powered for a few days.  This cleaned (or whatever happens) 
the tube and I was able to lock it.  FWIW, the supply I connected was 
about 7 kV.  The label said 3KV, but apparently that was under the rated 
load.  In any event, I thought I wrecked the whole thing.  I was assured 
by some time nuts that it was OK, and it was.  It's been running 
continuously now for about 2 months.  Here's an ADEV plot for fun...

   Measured against another opt 4.  Both units have an unknown history, 
and they are 40 year old tubes, so I consider this a success!  Good 
enough anyway.

Good luck, and keep one hand in your pocket.

Jim

On 2023-02-08 12:39 AM, Matt Krick via time-nuts wrote:
> Hello,
>
> I recently acquired a HP5061A and I am attempting to start it but there are
> some things that are puzzling me.
>
> Per the manual I have left the unit plugged in for 24 hours with mode set
> to CS OFF set to and I have observed the Ion Pump readings go to 0 after
> about 3 or 4 minutes of first plugging it in.
>
> So now I am attempting to power up the tube by switching to Loop open and I
> can hear another power supply engage. My Ion Pump reading climbs to about
> 30 after about 10 seconds and then the power supply shuts off. Then I get
> into a cycle of about 2 seconds on for 10 seconds off with the Ion Pump
> going between 20-30 or thereabouts.
>
> I'm not sure if this is normal and part of the pumping down process.
> Should I leave it on or keep trying to run it on CS OFF?
>
> Am I correct in assuming that with CS OFF the +3500V supply is running and
> that is what is acting as the Ion Pump to evacuate the tube, and then when
> I switch to Loop open that also powers  up the Cesium Heater and the -2500V
> supply?
>
> I have experience with high power Triodes and Tetrodes where you run the
> filaments without high voltage to help evacuate the tube so I'm unsure how
> a tube like this operates.
>
> Thank you!
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-- 

Jim Muehlberg
Senior Engineer

National Radio Astronomy Observatory
ngVLA Local Oscillator Lead

1180 Boxwood Estates Rd B-111
Charlottesville, VA 22903-4602
P 434.296.0270
C 434.422.2017