[time-nuts] HP5061B Ion Current

[Donald E. Pauly]

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

I posted another HP cesium beam tube patent at
http://gonascent.com/papers/hp/hp5061/US3387130.pdf .  It covers the
formation of the cesium beam and should be of interest.  We now have
over a month of operation on our first HP5061B at ion currents over 50
μA with no lock problems.  The uon pump voltage is 2,338 V at that
current.

We are still working for lock on our second HP5061B.  Both of the HV
power supplies had to be repaired and other problems remain.  Anyone
having supposedly unusable beam tubes with high ion current should
contact me at trojancowboy at gmail .com.



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

[Donald E. Pauly]

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

The patent that I posted at
http://gonascent.com/papers/hp/US3323008.pdf has many interesting
facts about the cesium beam tube.  It says that the temperature of the
cesium oven is 65° C.  I researched the vapor pressure of cesium at
various temperatures.  With a change of 30° C in the oven temperature,
the cesium pressure goes up or down by 10 to 1.  If the oven
temperature goes up by 5°C, cesium use rate goes up by 1.46 to 1.  If
it goes down by 5°C, cesium consumption decreases by 1.46 to 1.
Cesium oven temperature is quite critical to beam tube life.  The
HP5061A has a switch to reduce cesium oven temperature to increase
beam tube life at a price of slightly worse short term stability.

If the oven is shut off in CS OFF mode, pressure drops to 1.41x10^-6
Torr at 25 at temperatures about 25° C.  This is 2.8 times more that
the 5x10^-7 Torr that is considered a good vacuum for the tube.  good
vaccum is considered 2 μA on the ion pump. This would be 5.6 μA for
the higher pressure.  Therefore, the tube will get somewhat gassy if
the instrument is not used.  If it is stored at temperatures about 25°
C while not in operation, the situation is worse.  I don't know what
is causing higher currents but it must be contaminants beside cesium.

http://www.powerstream.com/vapor-pressure.htm

C°  log mm Hg
-18° -8
2° -7
22° -6
47° -5
77 -4
109° -3
155° -2
207° -1
252° -0

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

[cdelect]

Things to be careful about!

"I think the final vacuum improvement can be achieved more 
quickly if the cesium oven is on."

The outgassing in a tube that has been off for an extended time
is almost all from the oven filaments and the ionizer filament.
The metal surfaces are virtual "sponges" and getter any gases
that are available. If you turn them on with no protective 
cycling circuit you run the risk of overloading the ion pump 
to the point where it cannot pump at all!

Don't use the 200Meg divider voltage to determine the output 
voltage of the supply. Unloaded it is a correct representation
of the output voltage. (4Vdc equals 4000V out)However any 
appreciable load causes a counter voltage that drops the 
divider voltage a lot! The divider voltage might 
then read 1 volt but the output voltage is still over 3000V. 
(it's designed that way to shut off the ovens if the divider 
voltage drops.)Use a Fluke 80K-40 divider probe or similar 
on the output as it has a very high input impedance. A recent
measurement of 4 A18 supplies shows an output voltage of
3000 V with a 50ua load.

Also if testing the supply on the bench you must ground the case
of the supply to the minus input pin. If you don't your
HV will read half of what it should be.

Ion pump supplies for vacuum maintenance like for Cesium tubes, 
Hydrogen Masers, and some high power Rf TX tubes are just for that,
"maintenance". This allows low power consumption, small footprint,
and long life.

On the EFOS Maser here the ion pump supply has a max rating
of 2ma, this for a large 20 liter pump. 

If you are running a tube at high ion pump currents you might
have 20na of beam current but check the peak to valley ratio.
Just because you can get to 20 na does not mean the tube
is performing well. Running an Allan Deviation plot is the
easiest way to know for sure.

The oven filaments are very robust, the ionizer filament due to
the required shape is not. If you are using the older A11
module then the ionizer voltage is AC and causes vibration
of the filament which can result in premature failure. Once
HP came out with the new A11 (DC on the filament) they would 
not honor a tubes warranty if you were using the old style A11.

Cheers,

Corby Dawson

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Re: [time-nuts] HP5061B Ion Current

[paul swed]

I am listening and learning. Great point on the HV supplies.
When I look at the supplies I believe they are soldered cans. Is that
correct?

Further had not thought about the ionizer. Skips pictures of the CBT tube
clearly shows a popped ionizer.

There are two oven controllers AC or the DC version. I would strongly
believe the DC is quite easy to control through a FET and monostable. But
this approach simply prevents multiple trips if the ION pump is re-cycling.
AC maybe a bit harder. Have to actually look.

On Frankenstein I built a DC controller not realizing HP used DC in later
models so on that unit its very easy to do a soft start ramp.

Regards
Paul
WB8TSL


On Wed, Mar 22, 2017 at 9:33 AM, Scott McGrath  wrote:

> John makes a good point about the ionizer filament has anyone done a 'slow
> start' system for the Ionizer filament?
>
> I.e. Limit the inrush current as is done for expensive high power
> transmitting tubes?
>
>
>
>
> > On Mar 21, 2017, at 9:44 PM, Donald E. Pauly 
> wrote:
> >
> > It looks like that there is about 10% hysteresis on the cesium trip
> > off/on. That may not be enough to prevent cycling on and off.   I may
> > not have made it clear but instability in the +3,500 voltage makes a
> > big difference in the threshold ion current required for activation.
> > If it fades it can require a 10 uA smaller ion current to activate
> > cesium.
> >
> > -- Forwarded message --
> > From: John Miles 
> > Date: Tue, Mar 21, 2017 at 5:41 PM
> > Subject: Re: [time-nuts] Fwd:  HP5061B Ion Current
> > To: Discussion of precise time and frequency measurement
> > , rwa...@aol.com
> >
> >
> > 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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Re: [time-nuts] HP5061B Ion Current

[Scott McGrath]

John makes a good point about the ionizer filament has anyone done a 'slow 
start' system for the Ionizer filament?   

I.e. Limit the inrush current as is done for expensive high power transmitting 
tubes?




> On Mar 21, 2017, at 9:44 PM, Donald E. Pauly  wrote:
> 
> It looks like that there is about 10% hysteresis on the cesium trip
> off/on. That may not be enough to prevent cycling on and off.   I may
> not have made it clear but instability in the +3,500 voltage makes a
> big difference in the threshold ion current required for activation.
> If it fades it can require a 10 uA smaller ion current to activate
> cesium.
> 
> -- Forwarded message --
> From: John Miles 
> Date: Tue, Mar 21, 2017 at 5:41 PM
> Subject: Re: [time-nuts] Fwd:  HP5061B Ion Current
> To: Discussion of precise time and frequency measurement
> , rwa...@aol.com
> 
> 
> 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] HP5061B Ion Current

[Donald E. Pauly]

It looks like that there is about 10% hysteresis on the cesium trip
off/on. That may not be enough to prevent cycling on and off.   I may
not have made it clear but instability in the +3,500 voltage makes a
big difference in the threshold ion current required for activation.
If it fades it can require a 10 uA smaller ion current to activate
cesium.

-- Forwarded message --
From: John Miles 
Date: Tue, Mar 21, 2017 at 5:41 PM
Subject: Re: [time-nuts] Fwd:  HP5061B Ion Current
To: Discussion of precise time and frequency measurement
, rwa...@aol.com


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] HP5061B Ion Current

[cdelect]

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] HP5061B Ion Current

[Donald E. Pauly]

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

I could not figure out why the A15 Ion Current monitor would not let
the cesium oven turn on with ion current under 25 uA.  At the time we
had no way of measuring the +3,500 ion pump supply.  We bought some
200 Meg resistors and made a crude HV meter to feed our 10 Meg Fluke
77.  The supply had sagged to 2000 Volts with that load.  This
prevented the ion pump current monitor from energizing the cesium
oven.

KB7APQ unsoldered the can on the 3,500 Volt supply with suggestions
from WB4BBP.  It is a horrible design and we studied it.  R4 is set at
the factory to produce 3,500 Volts with no load.  It runs at 704
pulses per second and sags badly with the slightest load.  This
prevents the ion pump from clearing the gas in the beam tube.  The pot
core transformer is plenty big that it appears that the supply can put
out 5 mA at 3,500 volts.  This allows it to replace the external
supply recommended by HP for gassy tubes.

It looks like that it can run at 10 kc with existing pot core
transformer.  The pulse width looks like it can be doubled as well.
This allows for a 30 to 1 increase in output power.  A small circuit
board will regulate the voltage as well as limit the current.
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Re: [time-nuts] HP5061B Ion Current

[Hal Murray]

trojancow...@gmail.com said:
> We will discuss our findings if there is interest. 

This is time-nuts.  Of course there is interest.


What fraction of the old/dead tubes are "gassy"?

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] HP5061B Ion Current

[paul swed]

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

On Mon, Mar 20, 2017 at 7:44 PM, Donald E. Pauly 
wrote:

> This is my first post.  I just bought a non-working HP5061B on eBay
> for $350.  My old boss KB7APQ in Salt Lake City and I are working on
> it.  It came in from the Philipines in October of 2015 and was
> diagnosed with a bad physics package in March 2016 by AllTest in New
> Jersey.  We initially found an open R8 pot on the 5 mc oscillator
> A10A2 which was killing most of the output.
>
> Next we had ion current of about 25 uA which stayed up.  The book
> seems to indicate that this was low enough to enable the cesium oven.
> The analysis of the theoretical ion current for cesium turn on was
> very difficult.  We shorted the base emitter of Q6 on A15 board to
> override Cesium oven disable. The instrument then achieved lock with
> beam current of 20.  Ion current rose to 35 after cesium oven warm up
> and lock.
>
> We have made great progress on the +3500V power supply analysis.  We
> believe that many so called gassy tubes are perfectly functional up to
> 1 mA ion current.  Mean free path is on the order of 142 mm in that
> case or the length of the beam.  We will discuss our findings if there
> is interest.
>
> WB4BBP has been most helpful with our efforts.
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Re: [time-nuts] HP5061B Ion Current

[Pete Lancashire]

Do a search of the list and a few other sites. there is a LOT of
information on what challenges one can have.
And a lot of the information is practical.

As for as pumping a tube down, it took me pretty much a day + a whole
weekend, but it did go down to what was
scribbled on the door, and now takes less than a minute. I only turned mine
on either once every 2-3 months or when
I wanted to use it. Before the current issue of what looks like a power
supply going nuts, I got lock in no more that
203 minutes. If I was not going to use it, I would let it run for 30-45
minutes and shut it down for the next 'pump down'

-pete



On Mon, Mar 20, 2017 at 4:44 PM, Donald E. Pauly 
wrote:

> This is my first post.  I just bought a non-working HP5061B on eBay
> for $350.  My old boss KB7APQ in Salt Lake City and I are working on
> it.  It came in from the Philipines in October of 2015 and was
> diagnosed with a bad physics package in March 2016 by AllTest in New
> Jersey.  We initially found an open R8 pot on the 5 mc oscillator
> A10A2 which was killing most of the output.
>
> Next we had ion current of about 25 uA which stayed up.  The book
> seems to indicate that this was low enough to enable the cesium oven.
> The analysis of the theoretical ion current for cesium turn on was
> very difficult.  We shorted the base emitter of Q6 on A15 board to
> override Cesium oven disable. The instrument then achieved lock with
> beam current of 20.  Ion current rose to 35 after cesium oven warm up
> and lock.
>
> We have made great progress on the +3500V power supply analysis.  We
> believe that many so called gassy tubes are perfectly functional up to
> 1 mA ion current.  Mean free path is on the order of 142 mm in that
> case or the length of the beam.  We will discuss our findings if there
> is interest.
>
> WB4BBP has been most helpful with our efforts.
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> mailman/listinfo/time-nuts
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[time-nuts] HP5061B Ion Current

[Donald E. Pauly]

This is my first post.  I just bought a non-working HP5061B on eBay
for $350.  My old boss KB7APQ in Salt Lake City and I are working on
it.  It came in from the Philipines in October of 2015 and was
diagnosed with a bad physics package in March 2016 by AllTest in New
Jersey.  We initially found an open R8 pot on the 5 mc oscillator
A10A2 which was killing most of the output.

Next we had ion current of about 25 uA which stayed up.  The book
seems to indicate that this was low enough to enable the cesium oven.
The analysis of the theoretical ion current for cesium turn on was
very difficult.  We shorted the base emitter of Q6 on A15 board to
override Cesium oven disable. The instrument then achieved lock with
beam current of 20.  Ion current rose to 35 after cesium oven warm up
and lock.

We have made great progress on the +3500V power supply analysis.  We
believe that many so called gassy tubes are perfectly functional up to
1 mA ion current.  Mean free path is on the order of 142 mm in that
case or the length of the beam.  We will discuss our findings if there
is interest.

WB4BBP has been most helpful with our efforts.
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