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

[Jim Muehlberg]

OK, great info!  I am very nervous around HV, but now I understand that 
he A18 can't even handle the 10M input on the expensive Keitlhy DMM I 
foolishly connected.

Even with the high tension lead disconnected and well away from metal, 
the ion pump current is still pegged.

So, despite that, I built a divider which turned out to be 64.2MOhm.  
Across the 103K at the bottom I got 1.2V giving about 12 uA, so the 
supply is only delivering about 800 volts.  Is it really this wimpy?  if 
it normally delivers about 10uA, that suggests a 350MOhm Load.  So, I 
put in another few resistors and brought the total to ~172.3M, yielding 
0.472 across the 103K giving around 785V in.

I even went so far as to clean the vicinity of the A18 output.  Since my 
hearing is not wonderful, I could not detect any corona discharge or 
buzzing or whatever it's should sound like.

I suppose the final nail in the A18 coffin will be removing it and bench 
testing.  (BTW, the input voltage is good)

Thanks for all the help.

On 2022-11-14 9:35 PM, paul swed via time-nuts wrote:
> Here is a pix of a unit I was testing.
> [image: DSC04636.JPG]
>
> The current meter is in the lower leg of the return. You can see the high
> voltage probe on the right. I recall its 68 M and feeds a fluke DVM. The
> amp meter is measuring the current that the probe is consuming. The other
> connections are ground and +18.7V.
> The precision voltage divider in the background was not used.
> Testing the supply like this is fairly easy and just look at the schematics
> to understand how to hook everything up.
> Regards
> Paul
> WB8TSL
>
>
>
>
>
>
> On Mon, Nov 14, 2022 at 9:27 PM paul swed<paulswedb at gmail.com>  wrote:
>
>> Jim
>> OK I thought the thread said the meter is pegged and yes at turn on the
>> ion pump 3500 V is always on. The switching and protection I am speaking
>> about is for the other circuits. They will not start if the pump current is
>> to high. The ION pump sends a signal that inhibits their start. A 1M R is
>> far too low of a resistance its loading the supply down. Try something like
>> 40-60 Meg. Maybe a string of 10 M with a 100k R at the bottom. Measure the
>> V across the 100K. In normal operation the 3500 V will be drawing 4-14ua if
>> the tubes reasonably pumped down.
>> So thinking about this. There is a twist HV connector on the chassis that
>> the 3500 V goes through. I am reluctant to say this but if that were off
>> and far away from anything to arc to and the ion pump meter went to close
>> to zero then you would know the supply is most likely working and you have
>> a very dirty tube. I just do not like the thought of a 3500 V plug floating
>> free.
>> Regards
>> Paul
>> WB8TSL
>>
>>
>> On Mon, Nov 14, 2022 at 7:51 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
>>>>> _______________________________________________
>>>>> time-nuts mailing list --time-nuts at lists.febo.com
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>>>> _______________________________________________
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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 totime-nuts-leave at lists.febo.com
>>
>
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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