[time-nuts] Re: 5061A HV Supply, et al. {External}

Tue Nov 15 02:30:36 UTC 2022

Jim,

The 3500V supply is designed to be a soft supply that folds under load. A
1MOhm load is enough to make it collapse down to 750V. The meter display
estimates current by measuring how much the voltage sags.

If you want to measure open circuit voltage you'll need to get closer to a
1GOhm measurement impedance. If you want to crosscheck the current through
the ion pump you can unmount the tube and connect an ammeter between it and
the chassis (the return path for the ion pump) and measure the current
directly.

Thanks,

Chris

On Mon, Nov 14, 2022, 6:51 PM Jim Muehlberg via time-nuts <
time-nuts at lists.febo.com> wrote:

> Paul,
>
> My understanding is that the 3500 V is on as soon as power is applied.
> Disconnected, I get 750V at the HV lead.  I first connected a 1M Ohm
> resistor divider because I don't really have HV measuring stuff (10K to
> 1) and it read 350 V.  Indeed the meter is pegged, but I suspect that is
> due to some internal fault in the A18 as well.  So unless there is some
> turn on signal to the 3500 V supply, I suspect it is bad.  This whole
> thing may be a basket case.  No one knows the history.
>
> I'm also missing the divider assembly, so that may put the brakes on the
> whole project, but I'll worry about that once I have attempted to pump
> down.
>
> Thanks for the advice!
>
> Jim
>
> On 11/14/2022 3:25 PM, paul swed via time-nuts wrote:
> > Jim
> > I may be missing something here. Your suggesting the 3500 V ion pump
> supply
> > is bad.
> > But I believe the ion pump meter is pegged from an earlier post. If true
> > then the 3500 V is fine. If the tubes dirty and drawing too much current
> > there is a lockout circuit on a15 that will not allow the CS oven and
> 2500
> > V to come up until the ion pump is below about 15-20ua on the meter. It
> > senses the current being drawn by the 3500 HV. Enters a15 on pin 1 and
> > inhibits the rest of the system.
> > If my thoughts are correct then you need to pump down the tube as Rodger
> > says with a 3500 V supply and as I suggested 300 ua is way more than
> > enough. There is a chance the tube may work in a relative quality sense.
> > That is it could lock but there are so few Cs that the output of the
> system
> > is noisy.
> >
> > Regards
> > Paul
> > WB8TSL
> >
> >
> > On Mon, Nov 14, 2022 at 3:00 PM Jim Muehlberg via time-nuts <
> > time-nuts at lists.febo.com> wrote:
> >
> >> Rodger,
> >>
> >> Thanks for the encouragement!  I'm trying not to spend too much effort
> >> on this - sort of a distraction from real work.  One would think that
> >> NRAO would have a HV power supply lying around somewhere, but astronomy
> >> has gone solid state now for decades!  We have a grad student trying to
> >> nurse along another 5061 and we'd like to have a pair. I guess I'll
> >> slice open the A18 module and see what makes it tick.
> >>
> >> Thanks again,
> >>
> >> Jim
> >>
> >> On 11/10/2022 9:11 AM, Rodger via time-nuts wrote:
> >>> Hey Jim,
> >>>
> >>> I got a 5061a a couple years ago with high ION pump current.  In my
> case
> >> the 3500 volts was there but the tube was not pumping down, even after
> >> being on for weeks.  I found a Terranova 741 Ion pump power supply on
> eBay
> >> for under $100.  It was listed as not working but worked AOK when I got
> >> it.  It's a nice supply with variable output voltage, current limiting,
> >> safety interlocks, etc.  I hooked it up to the tube and let it run for a
> >> few weeks.  Tube pumped down successfully and is working AOK now.  My
> guess
> >> is that my A18 wasn't capable of supplying the current needed to pump
> down
> >> the tube but the external power supply was.
> >>> Note: I proceeded very carefully with the external supply, letting it
> >> run for days at lower voltages and gradually working up to 3500.  Also,
> I
> >> kept the current limit set as low as it would go.  Anyway, it worked for
> >> me.  Good luck with yours.
> >>> Rodger
> >>>
> >>> -----Original Message-----
> >>> From: Jim Muehlberg via time-nuts <time-nuts at lists.febo.com>
> >>> Sent: Wednesday, November 9, 2022 11:07 AM
> >>> To: time-nuts at lists.febo.com
> >>> Cc: Jim Muehlberg <jmuehlbe at nrao.edu>
> >>> Subject: [time-nuts] 5061A HV Supply, et al.
> >>>
> >>> I've recently come into possession of a 5061A.  It is claimed that the
> >> tube is exhausted, but I'm unwilling to scrap it (horrors!) yet.  I'm
> not
> >> well equipped for HV measurements, but it appears the +3500 V supply is
> not
> >> working.  So, I'm hoping the tube just needs to be pumped since it
> hasn't
> >> been powered for years.  Also missing the A3 assembly, but I'll worry
> about
> >> that later...
> >>> Anyone willing to part with their A18 or loan it to me?
> >>>
> >>> Thanks!
> >>>
> >> --
> >>
> >> 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
> >> F 434.296.0324
> >> www.cv.nrao.edu/~jmuehlbe
> >> _______________________________________________
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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
> F 434.296.0324
> www.cv.nrao.edu/~jmuehlbe
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com