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

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

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

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

The -2500 supply is nearly identical to the +3500 supply.  We will
post some photos on the disassembly process.  We also had to
disassemble the +3,500 supply because the 200 Meg resistor had gone up
in value.  It showed only 1,900 V with no load when it should have
shown 3,200 V.  We replaced the 47 uFd electrolytic with a tantalum as
a preventive measure.

After we repaired the -2,500 supply we measured the output voltage
versus beam current as set by front panel adjustment. Note that about
a 10% increase in electron multiplier voltage will double beam
current.

beam current  High Voltage
30                -1,755
20                -1,658
10                -1,507

On our freshly repaired HP5061B, we ran it four hours with no voltage
on the ion pump.  It maintained lock when voltage was reapplied.  Ion
current and voltage were unchanged at 76 uA and 2500 V.  You
apparently can operate for some time with no ion pump.

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

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

I Show you my boxed  TICC ready for the use.
The additions are:
-The input protection and 50/1M Ohm input selection.
-Some display led on the front panel.
best regards,
Luciano
www.timeok.it