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 trojancowboy@gmail.com
wrote:

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 trojancowboy@gmail.com
wrote:

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.

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 paulswedb@gmail.com
Date: Mon, Mar 20, 2017 at 7:08 PM
Subject: Re: [time-nuts] HP5061B Ion Current
To: Discussion of precise time and frequency measurement time-nuts@febo.com

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

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 reeeeally nervous.

-- john, KE5FX
Miles Design LLC

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

I have posted two HP patents on the cesium beam tube at
http://gonascent.com/papers/hp/US3323008.pdf and
http://gonascent.com/papers/hp/US3397310.pdf . Both are of academic
interest. The first claims that the cesium oven operates at 60°-70° C.
This is a tiny heating compared to a 1,000° filament on a power
transmitting tube.  I say that it can be cycled a million times with
no problem of thermal cracking.

πθ°μΩω±√·Γλ
WB0KVV

---------- Forwarded message ----------
From: John Miles john@miles.io
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
time-nuts@febo.com, rward0@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 reeeeally nervous.

-- john, KE5FX
Miles Design LLC

Yeah, I wouldn't worry about the oven, but the ionizer filament is a different story.  Those can definitely open up.

-- john,  KE5FX
Miles Design LLC