I believe that connector is one of many series of the Molex brand,
around nearly forever. I wouldn't let that be a problem - cut and splice
works just fine.

For juicing it up, first take some measurements (and assuming the unit
is plugged in somewhere to line for overall power) to see if any kind of
electrical signal is present at the connector pins - maybe as simple as
a contact closure to activate. If it looks like there's no power and
passive, then check for resistance and semiconductor junctions, to see
if there's a relay coil or device input.

Those connectors are rated for line voltage, so it could be set up for
that level of input, but I doubt it.

My guess is that it's for Class 2 low voltage control, by contact
closure or pulse input. You should be able to get it going OK after some
study.

If this is a master timing signal for multiple clocks, then of course it
would need provision for fast advancing and such, and somehow
synchronizing them all. One way would be a master reset signal to all
12:00, then fast forward the right number of counts. I think I recall
the old school and factory/office clocks did something like this.

Maybe one polarity of pulses to advance, and reverse polarity to reset,
for instance.

Ed

One more thing. I recall the major brand of "system" clocks in the old
days was Simplex. They probably set the standards for how these things
work, so there may be lots of info available.

Ed

A simple and expedient solution is to just get a fresh BME280 (or maybe
a bunch of them for spares). Temperature measurement devices can have a
very long service life, but absolute pressure and RH devices degrade due
to reference leakage and contamination, respectively.

Small and relatively low cost consumer grade parts may work fine for a
while, but should probably be viewed as consumables in the system. So,
for less than a hundred bucks, you could have say a dozen BME280s
stashed away, and figure on changing them like light bulbs every three
years or so, if necessary. If your original one failed prematurely for
some reason, then they could be actually much more reliable, and you may
never have to change another, but they'll be there just in case.

One way to get very long life and stability in absolute pressure is to
use industrial grade transducers that have a fairly large reference
volume, are mostly high grade metals (typically SS and Inconel), truly
hermetic and welded shut, and even gettered, to get down to very stable
vacuum. That all is partly why they're so expensive.

For RH, I agree with Bob and Jim that a chilled-mirror dew point
measurement device is best and longest-lasting, due to the ability to
clean and maintain the working parts. And, you can indeed roll your own
without too much grief.

Ed

Fans provide at least three kinds of noise. The audible is most annoying
to humans, but we can adapt. The electric and magnetic noise may
interfere with the instrument - we definitely don't want that.

If you're fixing or modifying a fan problem in a high performance,
precision instrument, it's probably best to not stray too far from using
the same parts and circuit design as the original. The reason is that
you don't know - without some study and consideration - how much the fan
interacts with or affects the rest. What you do know is that the
original setup did its job, and the instrument (likely) met its specs.

You may be able to not only fix the problem, but also improve the
overall performance with different fans and driving methods, but it
takes some study to make sure.

A good thing to consider first is the location and proximity to possibly
sensitive circuitry. If the fan is say, bolted to the back, and faces
only power supply circuitry, and is nowhere near anything critical, then
it's probably safe to not worry much about the magnetic fields coming
from the motor. This allows for more options in fan choice, like AC
versus DC.

Next is thermal - how well does it actually cool the innards? You have
some leeway here too, since stock fans are usually chosen to work at the
highest specified ambient temperature, and in rack mount situations. If
your environment is more friendly, you can go with less fan air flow,
which almost always allows for more peace and quiet. This can take a lot
of experimenting to figure out how low you can go, and still be safe,
cooling-wise.

Finally, you have to consider the electric power situation. Regardless
of fan type, there will be motor ripple currents from the AC line or
from the DC supply. These can affect the source, and also radiate EM
fields from the wiring, so the paths may be important too - avoid the
sensitive areas, or shield the lines properly. For AC induction motors,
it is what it is, while for DC, lots of filtering close to the motor
helps. You might be surprised at how much commutation current even a
small brushless DC fan can produce. You can do some experiments to study
it and assess the ugliness.

It may take a lot of capacitance to get acceptable ripple, especially if
the fan supply is not isolated well from the supplies that run the
critical circuitry. In extreme cases, a shunt regulator right at the fan
(electrically close as possible) can make it invisible to the PS,
leaving only the wiring between the shunt and the motor to radiate.

There's no reason nowadays to use a brushed DC or universal motor for a
small equipment fan - leave those for hair dryers. I think virtually all
modern small DC fans are brushless PM, and can run over quite a speed
range. These are best for most equipment. For reduced speed, lower
noise, try fixed lower voltages, and be sure that the motor will
properly kick-start from off or stall (these are two different
situations, even though the speed is zero) under all conditions.

For variable speed, analog is of course cleanest, but the power
dissipation may become an issue, depending on fan size. PWM is more
efficient, but adds another layer of EMC consideration. I always try to
avoid adding SMPS/PWM circuits in low noise gear, but in many cases, the
stuff is already powered by such, so adding a little more isn't
necessarily bad. The trick is to figure out what problems may arise, and
how to handle it.

One more thing about AC fans. Most of my old gear has the classic
pancake AC fans, loud as hell. In some, I have changed to lighter gauge
fans (the usual solution), or modified the circuits to run them slower.
It all depends on the particular fan models. I test fans on the curve
tracer or variac to see how they do at low or variable speeds. Some
models are awesome, able to reliably start and run over a huge
voltage/speed range, while others are awful, unable to start properly at
all, then go flakey and wind up to jet engine noise level once the
voltage is high enough. The fans that do reasonably well or great are
marked and reserved for low speed transplants back into equipment

Ed

I doubt that the laser supply hurt the A18. If it did, it would have
likely broken the rectifiers in reverse, and you wouldn't be getting the
normal HV and 4 V monitor signal and almost-working behavior afterward.

I assume this laser supply is the kind for small HeNe tubes. These
things have provisions for striking the tube with higher voltage to get
it going. It's not unusual for the unloaded output to get up to 15 kV or
so, either continuous, or as ignition spikes superimposed on a medium HV
output. Once the tube lights, it loads it down to the normal operating
power of the tube plus the ballast resistor, and it stops trying to
light it up.

This could be a handy unit to serve as the external HV source to
possibly restore the Cs tube. You just have to add a few things around
it to make it do approximately the right thing. In principle, all you
need is to load the supply down just right to get the right voltage and
fool it into thinking it's running a stable HeNe tube, drawing the
normal current or power range, and not trying to strike or re-strike.

These things are not very smart or precise, so you have lots of room to
tweak things around without too much grief. I'm going to make some
assumptions about the power supply and the HV tools and parts you may
have at your disposal.

First, if you actually had 7 kV output continuous for a few minutes, I
assume the supply is a constant-power flyback type, so the output likely
can reach 10-15 kV or so to strike the lamp, and does not use an
ignition pulse circuit. This is best for the application, since you
won't have it decide to make nuisance pulses. You can't tell yet for
sure if this is the case, until you scope it out.

The main HV tool you seem to have is the "172 meg divider," which I
assume is a string of megohm range resistors. Do you believe it can take
10 to 15 kV for a short time without breaking down or overheating?
You've already proofed it to 7 kV, no sweat. If it can take the higher
voltage, it makes it more convenient, but it's not absolutely necessary.

Now thinking about the supply rating and characteristics, it normally
would be running a small (like 0.5 mW) HeNe tube plasma load, plus a
ballast around maybe 75 k ohm or more, at the nameplate 1250 V by 4 mA,
so 5 W going in. The ballast swamps out the tube's negative resistance,
and drops say 300 V, leaving about 950 V on the tube.

Since we're assuming approximately constant output power, and we know it
can reach 7 kV at some load, then it can easily reach the desired 3,500
V ion pump supply level. This is 2.8 times the normal laser voltage, so
the available current should be around 4 mA/2.8 = 1.43 mA, which is a
very nice current level in the scheme of things here. So, that 5 W gives
a good current at the desired higher voltage, just by loading it down
right. A load of 3,500 V / 1.43 mA is about 2.5 megs, which should be
readily realizable with a decent resistor inventory. It would be an
assembly of lots of whatever resistors it takes to get the right value
and handle over 3,500 V, and over 5 W total power dissipation.

So, if you start with something around 2.5 megs, 10 W, 5 kV max rating,
and hook up your 172 meg divider to monitor the situation, you can see
what it's doing, and tweak the system accordingly. This all is without
any hookup to the 5061A, just all by itself until it's ready.  At this
point you can also scope it - hook it to the HV divider output and look
for any signs of ignition pulses that may cause trouble. Note that the
frequency response will be quite low. I'm guessing you'll just see some
high frequency ripple from the laser supply. If it is re-striking, then
certain changes may be in order to suppress it, or it may not even
matter for this purpose.

You can also form a divider into the load resistor assembly itself, so
you can monitor it at any time, at some some convenient scaling factor
like 1000x. For instance, in a very simple form, whatever the load R
needs to be for the right voltage, you can put 99.9 percent of it in the
power section, and 0.1 percent in series at the bottom. Or, the divider
can be a small portion of all the resistors that make the whole thing.

Once you proof it, then it can be attached to the Cs tube, and you can
see what it's doing voltage-wise. With no tube load, your PS circuit
should be around the right 3,500 V nominal, and can only go down from
there as it pulls ion current.

BTW these little constant-power supplies can be dangerous, since they
can put out quite a bit of current as the voltage drops. A 125 V shock
can pump 40-50 mA through your arm or whatever, with good contact.
Always be careful.

Ed

Hello,
Have a look at the Bertan/Spellman catalog : I have used their modules for the 5061A/B and the 5062C and some can be enclosed in the HP HV original cans...
On Thursday, December 1, 2022, 03:33:44 PM GMT+1, ed breya via time-nuts time-nuts@lists.febo.com wrote:

I doubt that the laser supply hurt the A18. If it did, it would have
likely broken the rectifiers in reverse, and you wouldn't be getting the
normal HV and 4 V monitor signal and almost-working behavior afterward.

I assume this laser supply is the kind for small HeNe tubes. These
things have provisions for striking the tube with higher voltage to get
it going. It's not unusual for the unloaded output to get up to 15 kV or
so, either continuous, or as ignition spikes superimposed on a medium HV
output. Once the tube lights, it loads it down to the normal operating
power of the tube plus the ballast resistor, and it stops trying to
light it up.

This could be a handy unit to serve as the external HV source to
possibly restore the Cs tube. You just have to add a few things around
it to make it do approximately the right thing. In principle, all you
need is to load the supply down just right to get the right voltage and
fool it into thinking it's running a stable HeNe tube, drawing the
normal current or power range, and not trying to strike or re-strike.

These things are not very smart or precise, so you have lots of room to
tweak things around without too much grief. I'm going to make some
assumptions about the power supply and the HV tools and parts you may
have at your disposal.

First, if you actually had 7 kV output continuous for a few minutes, I
assume the supply is a constant-power flyback type, so the output likely
can reach 10-15 kV or so to strike the lamp, and does not use an
ignition pulse circuit. This is best for the application, since you
won't have it decide to make nuisance pulses. You can't tell yet for
sure if this is the case, until you scope it out.

The main HV tool you seem to have is the "172 meg divider," which I
assume is a string of megohm range resistors. Do you believe it can take
10 to 15 kV for a short time without breaking down or overheating?
You've already proofed it to 7 kV, no sweat. If it can take the higher
voltage, it makes it more convenient, but it's not absolutely necessary.

Now thinking about the supply rating and characteristics, it normally
would be running a small (like 0.5 mW) HeNe tube plasma load, plus a
ballast around maybe 75 k ohm or more, at the nameplate 1250 V by 4 mA,
so 5 W going in. The ballast swamps out the tube's negative resistance,
and drops say 300 V, leaving about 950 V on the tube.

Since we're assuming approximately constant output power, and we know it
can reach 7 kV at some load, then it can easily reach the desired 3,500
V ion pump supply level. This is 2.8 times the normal laser voltage, so
the available current should be around 4 mA/2.8 = 1.43 mA, which is a
very nice current level in the scheme of things here. So, that 5 W gives
a good current at the desired higher voltage, just by loading it down
right. A load of 3,500 V / 1.43 mA is about 2.5 megs, which should be
readily realizable with a decent resistor inventory. It would be an
assembly of lots of whatever resistors it takes to get the right value
and handle over 3,500 V, and over 5 W total power dissipation.

So, if you start with something around 2.5 megs, 10 W, 5 kV max rating,
and hook up your 172 meg divider to monitor the situation, you can see
what it's doing, and tweak the system accordingly. This all is without
any hookup to the 5061A, just all by itself until it's ready.  At this
point you can also scope it - hook it to the HV divider output and look
for any signs of ignition pulses that may cause trouble. Note that the
frequency response will be quite low. I'm guessing you'll just see some
high frequency ripple from the laser supply. If it is re-striking, then
certain changes may be in order to suppress it, or it may not even
matter for this purpose.

You can also form a divider into the load resistor assembly itself, so
you can monitor it at any time, at some some convenient scaling factor
like 1000x. For instance, in a very simple form, whatever the load R
needs to be for the right voltage, you can put 99.9 percent of it in the
power section, and 0.1 percent in series at the bottom. Or, the divider
can be a small portion of all the resistors that make the whole thing.

Once you proof it, then it can be attached to the Cs tube, and you can
see what it's doing voltage-wise. With no tube load, your PS circuit
should be around the right 3,500 V nominal, and can only go down from
there as it pulls ion current.

BTW these little constant-power supplies can be dangerous, since they
can put out quite a bit of current as the voltage drops. A 125 V shock
can pump 40-50 mA through your arm or whatever, with good contact.
Always be careful.

Ed

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