Re: [time-nuts] Fwd: HP5061B Ion Current

[paul swed]

Donald,
Very good and it is as I thought. No real magic a tough job.
Whats good about the suspended approach is it preserves the can nicely.
I have done a pry (small screw driver or xactor blade) and drip approach
and it actually slightly bends the can lip out.
I have never opened one of the HV supplies. But have had to open filters.
They can be put back together but never as nicely as the approach you are
using that should leave the can in optimal shape.
Thanks for sharing some very good insights.
Have you come up with a good 200 M replacement yet?
Regards
Paul
WB8TSL

On Tue, Mar 28, 2017 at 5:37 PM, Donald E. Pauly 
wrote:

> https://www.febo.com/pipermail/time-nuts/2017-March/104374.html
>
> We continue troubleshooting our 2nd HP5061 acquisition.  The 200 Meg
> resistor in the +3,500 V supply had gone way up in value and made it
> appear that the supply was half normal voltage.  See the black
> resistor in http://gonascent.com/papers/hp/hp5061/3500top.jpg .  We
> installed a temporary resistor.  The ion current was pegged when we
> reinstalled the supply.  This is not surprising since instrument has
> been stored for over a year.
>
> Here is the way that KB7APQ unsoldered the latest two high voltage
> supplies. See  http://gonascent.com/papers/hp/hp5061/desolder.jpg .
>
> High Voltage Power Supply Unsoldering and Repair
> 1 - Suspend power supply on steel wires using 6-32 ground lugs and nuts.
> 2 - Heat solder joint evenly all the way around using a propane torch.
> Be careful to avoid too much heat on connections. Act as quickly as
> possible to avoid overheating components.
> 3 - Pull down firmly on outer can while wearing a welding glove.
> Rotate unit until can comes away from power supply. Cold solder on the
> inside of the can can prevent power supply from sliding all the way
> out. You may want to shake off some excess solder as it melts.
> 4 - When can slides off of the power supply turn it over and tap it on
> the floor to remove excess solder from the inside of the can.
> 5 - Mark can for mounting holes to be used to reattach outer can after
> repair. I used 0.970 inches from the can side and 0.100 inches from
> the open end. The off center 0.970 dimension is to avoid power supply
> screws from interfering with each other in the event both power
> supplies need this modification.
> 6 - Center punch where marked then insert power supply back into can.
> Note the orientation for the label on top. Using a number 50 drill
> bit, drill through both can and base.
> 7 - Tap holes in the base using a number 2-56 tap.
> 8 - Enlarge the holes in the outer can using a number 43 drill bit.
> 9 - Use 2-56 x 1/8" pan head screws to secure the outer can.
>
> πθ°μΩω±√·Γλ
> WB0KVV
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[time-nuts] Fwd: HP5061B Ion Current

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-March/104374.html

We continue troubleshooting our 2nd HP5061 acquisition.  The 200 Meg
resistor in the +3,500 V supply had gone way up in value and made it
appear that the supply was half normal voltage.  See the black
resistor in http://gonascent.com/papers/hp/hp5061/3500top.jpg .  We
installed a temporary resistor.  The ion current was pegged when we
reinstalled the supply.  This is not surprising since instrument has
been stored for over a year.

Here is the way that KB7APQ unsoldered the latest two high voltage
supplies. See  http://gonascent.com/papers/hp/hp5061/desolder.jpg .

High Voltage Power Supply Unsoldering and Repair
1 - Suspend power supply on steel wires using 6-32 ground lugs and nuts.
2 - Heat solder joint evenly all the way around using a propane torch.
Be careful to avoid too much heat on connections. Act as quickly as
possible to avoid overheating components.
3 - Pull down firmly on outer can while wearing a welding glove.
Rotate unit until can comes away from power supply. Cold solder on the
inside of the can can prevent power supply from sliding all the way
out. You may want to shake off some excess solder as it melts.
4 - When can slides off of the power supply turn it over and tap it on
the floor to remove excess solder from the inside of the can.
5 - Mark can for mounting holes to be used to reattach outer can after
repair. I used 0.970 inches from the can side and 0.100 inches from
the open end. The off center 0.970 dimension is to avoid power supply
screws from interfering with each other in the event both power
supplies need this modification.
6 - Center punch where marked then insert power supply back into can.
Note the orientation for the label on top. Using a number 50 drill
bit, drill through both can and base.
7 - Tap holes in the base using a number 2-56 tap.
8 - Enlarge the holes in the outer can using a number 43 drill bit.
9 - Use 2-56 x 1/8" pan head screws to secure the outer can.

πθ°μΩω±√·Γλ
WB0KVV
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Re: [time-nuts] Fwd: HP5061B Ion Current

[paul swed]

Really good pix on the inside of the 3500V module. So the opening of the
can is the typical lots of heat and pry it open approach right?
How about a good pix of the 2500 Volt module?
Thanks
Paul
WB8TSL

On Sun, Mar 26, 2017 at 6:42 PM, Donald E. Pauly 
wrote:

> https://www.febo.com/pipermail/time-nuts/2017-March/104374.html
>
> We continue to try to achieve lock on our latest HP5061B acquisition.
> We found that the -2,500 supply would only come up to -780 V under
> normal 55 Meg multiplier load.  When we pulled off the HV lead to the
> beam tube, it came up to only about -1,500V.  After another horrible
> desoldering job, Q2 collector waveforms were essentially normal.  We
> found a near open C1 which is 47 μFd at 35 Volt electrolytic was open.
> This caused massive spikes on the bypassed +18.7 line.  We replaced it
> with a tantalum.  This brought it up to normal -2,700 V for full
> clockwise beam adjust on R7.
>
> Next we found that the +3,500 supply was only up to 1,000 V with
> normal ion current load.  We expect to find the same problem on this
> supply.  See http://gonascent.com/papers/hp/3500top.jpg.  C1 cannot be
> seen in this photo.  Ion current was only 15 μA because of the low
> supply voltage.  I will have another post on what we found about
> electron multiplier voltages.
>
> DEP
>
> πθ°μΩω±√·Γλ
> WB0KVV
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[time-nuts] Fwd: HP5061B Ion Current

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-March/104374.html

We continue to try to achieve lock on our latest HP5061B acquisition.
We found that the -2,500 supply would only come up to -780 V under
normal 55 Meg multiplier load.  When we pulled off the HV lead to the
beam tube, it came up to only about -1,500V.  After another horrible
desoldering job, Q2 collector waveforms were essentially normal.  We
found a near open C1 which is 47 μFd at 35 Volt electrolytic was open.
This caused massive spikes on the bypassed +18.7 line.  We replaced it
with a tantalum.  This brought it up to normal -2,700 V for full
clockwise beam adjust on R7.

Next we found that the +3,500 supply was only up to 1,000 V with
normal ion current load.  We expect to find the same problem on this
supply.  See http://gonascent.com/papers/hp/3500top.jpg.  C1 cannot be
seen in this photo.  Ion current was only 15 μA because of the low
supply voltage.  I will have another post on what we found about
electron multiplier voltages.

DEP

πθ°μΩω±√·Γλ
WB0KVV
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[time-nuts] Fwd: HP5061B Ion Current

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-March/104374.html

The design on the voltage and current limiter is complete but not
breadboarded yet. We are getting a little more time on our HP5061B
beam tube after beefing up the +3,500 Volt power supply.   We have the
frequency control R4 turned all the way up to 1900 cps with beam tube
ion pump load.  We have a shunt across the ammeter so it can measure
100 μA full scale instead of 50μA.  We dare not disconnect the load
because voltage limiting is not operational yet.  Continuous lock
light is lit.  Note that lock is normal at over 3 times what the book
said was normal cesium turn on point.  If we could go to +3,500 Volts,
the current would likely be 100 μA.  I calculate that lock would be
normal at 1 mA ion pump current.

time   μA voltage
08:46 56  3,620
09:46 70  3,400
11:25 72  3,360
12:58 76  3,300

We just got in our second HP5061B yesterday  It's ion current was only
14 μA but we haven't checked the voltage on the +3,500 V supply yet.
It appears to have a problem with the -2,500 V supply.

πθ°μΩω±√·Γλ
WB0KVV
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[time-nuts] Fwd: HP5061B Ion Current

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-March/104374.html

You bring up an interesting point.  As the cesium is used up over the
years, it forms a cesium frost which deposits on everything inside the
tube.  If it gets thick enough it conducts or can arc between frost
grains.  A charged capacitor can blow some of this away.  Cesium melts
at 83° F.  If you heated the beam tube up in a hot car or out in the
hot sun, you could turn this frost into dew.  The dew might run down
hill into some cesium lakes where it was harmless.  Those lakes would
freeze when back at room temperature and might be even more harmless.

I have seen two TV picture tubes that developed leakage between focus
and screen electrodes.  Adjusting focus changed the brightness and
adjusting the screen changed the focus.  I applied the high voltage
between the two and the arc burnt out the high resistance leak.  It
saved both picture tubes.

WB0KVV

πθ°μΩω±√·Γλ

If you cannot get the ion current below 50ua or so after a week at 5kV
then you are out of luck. Most likely you have resistive deposits on
the ion pump insulator. If you can get the tube to give a decent SN at
those levels then you can
run with the alarm circuit bypassed.

I have run tubes a couple years this way (at <50ua) but if you let them
sit cold you will have to manually cycle the ovens at turn on until the
excess gas load is pumped. If you have a bad ion pump supply when you
open it up to repair it I would suggest adding a 66K resistor across
the 75K resistor. This will increase the alarm trip up to about
40-45ua. If it's the older one the oil capacitors will need changing
as well as the 200Meg resistor.

If the later one (in the 5061B) then the 47uf radial cap is open. both
these units are interchangeable. One other trick is to use a spark
discharge tester (miniature hand held tesla coil used in the neon sign
industry) to ZAP the ion pump lead. This can blow out any whiskers
that the ion pump has developed. You can
also (carefully) with the HV on, remove and replace the ion pump
connector a few times. Sometimes you will get a sharp discharge that
blows out the whisker. I have used both methods with good success.

Cheers,

Corby

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Re: [time-nuts] Fwd: HP5061B Ion Current

[John Miles]

That's some very nice work, Donald.  Looking back, I have junked one or two Cs 
tubes that might have been usable if I'd thought through the problem of high 
ion pump current as you and KB7APQ seem to have done. 

Another good reason to raise the lockout threshold would be to cut down on the 
repetitive ionizer filament cycling that the tube will otherwise undergo when 
you first fire up the oven.  That phenomenon always makes me rally nervous.

-- john, KE5FX
Miles Design LLC

> -snip-
> When we overrode the cesium lockout at 29 μA or so of ion current, we
> needed only minor front panel adjustments for beam current of 20 μA.
> (We shorted across A15 R-4.) Our last ion current before power supply
> modifications at risen to 39 uA.  Beam current has been stable.
> 

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[time-nuts] Fwd: HP5061B Ion Current

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-March/104374.html

Paul:

I don't think that I made myself clear.  This power supply is a rare
example of HP engineering incompetence.  The transformer is EASILY
capable of 10 Watts out at 3500 V.  Instead they made it where it
can't even put out 100 mW without sagging.  This supply was designed
in the middle 80s when IC technology was well developed.

>From what I am able to determine about ion pumps, current is
proportional to pressure and voltage is proportional to pumping rate.
Paragraph 4-349 of the HP5061B manual states that 2 μA ion current
corresponds to a pressure of 5x10^-7 Torr.  At 760 Torr, the mean free
path of an oxygen molecule is 93 nm.  Assuming that a cesium atom is
the same size, this gives it a mean free path of 141 meters.  This
means that there is a 50% chance of a collision in a 141 meter travel
thru such a vacuum.  At an ion current of 1 mA, the pressure would be
500 times greater and the mean free path 500 times less or 0.282
meters.  This is 11" or about the length of travel for the beam in the
tube. A beam current of 1 mA would only cause a loss of 50% in beam
current and should still allow lock.

That same paragraph claims that cesium is turned on at 40 μA.  That
was not true.  Another place claims 20 μA (Appendix A-1 b) as well as
30 to 40 μA.  The exact trip point depends on how much sag occurs in
the HV supply and is very complex to calculate.  It is stupid to have
to wait for weeks for a reduction in ion current to allow the cesium
to come on naturally.  Lock can be achieved instantly.   I think the
final vacuum improvement can be achieved more quickly if the cesium
oven is on.  It should cook off cesium that has condensed on its
outside.

See page 8-51 schematic.  We measured the properties of the power
supply as it is.  For 18.7 V supply, 357 μH and 20 μs, energy stored
is in T1 primary is 108 μ Joules.  Frequency can be adjusted from 524
to 2002 cps.  Power supply with no load was set to 704 cps for +3,500V
out with no load except for the internal 200 Meg bleeder.  Input power
was 76.3 mW and output power was 61.25 mW or 80% efficiency.  At
frequencies above 704 cps, output voltage increases above safe levels
for no load.

With gassy beam tube for load, voltage sags to 2296 V with 39 μA ion
current 11.4 μA bleeder current.  Total power is 115.9 mW.  With
frequency raised to 55 μA ion current, voltage was 2460 V or 165 mW
power.  With frequency turned all the way up to 2002 cps, voltage was
2562 V and 71.4 uA ion current or 215 mW power.

We are working on a voltage regulator and current limiter that will
provide at least 1 mA before voltage reduction from +3500V.  This is
an improvement of at least 20 to 1. Output power is limited by the 21
kc self resonance of the transformer due to secondary winding
capacitance.  We don't know its saturation current yet. We plan to use
the two unused meter switch positions to monitor output voltage and
current.  It will likely mean that no external 3500 volt supply will
ever be required for tubes that have been in long storage.

I made a typo on WB4BPP's call in my first post but he reports using a
5,000V external supply.  He didn't provide current figures or whether
this voltage actually stayed there.  I am concerned about arc over at
the ion pump at that voltage.  Ion pump manufacturers caution about
overheating at high pump currents.  HP claims in Appendix B A-2 h that
+3500 V at 5 mA for no more than 15 minutes is permissible.  This is
17.5 Watts which sounds like a lot for a small cathode.

When we overrode the cesium lockout at 29 μA or so of ion current, we
needed only minor front panel adjustments for beam current of 20 μA.
(We shorted across A15 R-4.) Our last ion current before power supply
modifications at risen to 39 uA.  Beam current has been stable.

WB0KVV

πθ°μΩω±√·Γλ

-- Forwarded message --
From: paul swed 
Date: Mon, Mar 20, 2017 at 7:08 PM
Subject: Re: [time-nuts] HP5061B Ion Current
To: Discussion of precise time and frequency measurement 

Donald welcome to the group. If a units been off a long time and it sure
sounds like thats the case it may take quite a while like a month or so for
the unit to remove all of the "Stuff" that has out gassed. So be patient
and let the pump do its job. After it does lower and my fingers are
crossed. Then you only need to run it about every 6 months.
The fact that it actually locks and you found a simple fix is pretty good.
What was the beam current?? That gives you a hint on the quality of the
tube.

Not sure I would run the defeat on the HV supply for to long. That may
stress the supply if I had to guess.
Regards
Paul
WB8TSL
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