Unkjown ALC argon laser

[Laserbuilder]

Hi!

Does anyone have any information on this laser unit? This is definately an argon laser made by ALC company for a Carl Zeiss medical machine. The test label on it tells that it had a 5W output at 30A tube current and 2W at 20A. I am particularly interested in the cathode filament voltage and tube voltage drop value.

[mixedgas]

Hi!

Does anyone have any information on this laser unit? This is definitely an argon laser made by ALC company for a Carl Zeiss medical machine. The test label on it tells that it had a 5W output at 30A tube current and 2W at 20A. I am particularly interested in the cathode filament voltage and tube voltage drop value.

I actually have full schematics, as well as a friend that used to service those. I'll call him and see if I can get you cathode numbers. Basically it is a modified ALC HGM Division 905 or 909 medical tube. (Called 909Z by the www.Laserfreak.de people) However, many of them had LEXEL tubes similar to an 85 or 88 installed when ALC went bust. The power supplies are similar, but not the same if the short Lexel tube is installed.

The original power supply is known as the "Zeiss Switcher" and I haven't seen one for a decade.

This was semi-pulsed duty, so the tube would set at Idle current and "pop up" to the treatment power for milliseconds to hundreds of milliseconds, and drop back down to Idle. Hence the five watt number, which is to ensure that two or three watts made it to the patient down the fiber if the laser resonator was miss-aligned from drift in the optics or fiber coupler. Usually surgeons run them at 350 mW to 1000 mW delivered to tissue.

The test numbers on the side of the tube are related to pulsed service, you need to de-rate them for CW service. Basically a two to two and a half Watt or so argon when ran CW. Again, the 5 watt number is a peak when massively overdriven.

Would you please take a close up picture of the cathode and anode ends so I can see which tube you have? I have the Lexel numbers, I need to call my friend for the ALC numbers. The cathodes are grossly different in voltage/current ratings. Also the magnet coils are very different.

Percent green power is a specification on ophthalmic laser heads. Blue at 488nm is preferred for some tissue cauterization treatments with lots of blood present, so a blue/green / all lines filter arrangement is often present on medical lasers. A few eye treatments do better with the 514-530 spectrum. So blue/green ratio is important at tube installation, hence the specification. Green falls off first as tube ages.

22 Amps is a lot for those tubes, we used to prefer to run them at 15 to 18 amps in laser show service.

A rare later variant had an SP whitelight in it.

Zeiss called it "Visulas II "Visulas II

Steve

[mixedgas]

From www.laserfreak.de archives, I quote:

"
Ich hab in den letzten Tagen mal in den Archiven der anderen Laserforen gegraben und noch ein paar Spuren über unseren heißgeliebten ALC 909 gefunden. Die entsprechenden Posts (Links unten) enthalten jeweils nur homöopatische Spuren, ich fasse mal zusammen:

(1) Zeiss hat den Visulas zuerst mit einem Lexel 88 (85?) herausgebracht
(2) Der ALC 909Z ist ein kompatibler Ersatz für den Lexel und hat eine viel größere Kathode als letzterer
(3) Der 909Z ("Zeiss head") hat Brewster aus geschliffenem Quarzkristall statt Quarzglas (wie der 88?), und
(4) er war eher in Europa beliebt und verbreitet.

Paßt am besten hierher, dachte ich. (2) und (3) sind, wenn ich die Posts richtig interpretiere, für die viel höhere Leistung verantwortlich, die man aus einer 909Z-Röhre herauskitzeln kann.

~medusa.
"

Translates to:

n the last few days I have been digging in the archives of the other laser forums and found a few traces about our beloved ALC 909. The corresponding posts (links below) only contain homeopathic traces, I'll summarize:

(1) Zeiss first brought out the Visulas with a Lexel 88 (85?)
(2) The ALC 909Z is a compatible replacement for the Lexel and has a much larger cathode than the latter
(3) The 909Z ("Zeiss head") has Brewster made of cut quartz crystal instead of quartz glass (like the 88?), And
(4) it was rather popular and widespread in Europe.

Best fit here, I thought. If I interpret the posts correctly, (2) and (3) are responsible for the much higher power that can be teased out of a 909Z tube.

Medusa

END QUOTE

[bradstockdale]

I have a 909Z and ZPS switcher in working order. Pics in my albums. Have schematics. Steve's got you covered though.

[mixedgas]

Brad if you have schematics that would save me a lot of time right now...

More from my friend in Germany...

The ignition box from the ALC 909Z generates everything it needs from the 300V (tube) open circuit voltage of the power supply unit. Only the control input, which is internally separated by an optocoupler, has to be connected to an external 9-15V. The input is labeled "L + / L-" on the circuit board, on my box there was a coaxial cable with a BNC connector at the end.
If you add a 9V block battery and a button, the whole box can be operated quite well as a stand-alone device.

Debounce the signal to the optocoupler. make it a sharp square wave. Weak or oscillating control signals have a habit of causing ignition down the gas return bores in the tube. This is by generating too weak a pulse.

Steve

[mixedgas]

Lexel 88D model, 3.2 VAC center tapped, plasma off, Cathode I around 26.5 with plasma off, lit 27 to 27.5 amps. Vtube 165 or so, Tdesign for cathode = 1050 to 1100'C

ALC 909Z, 3.5 to 4 volts center tapped, cathode current 20 to 25 amps, tube voltage 215 vdc average, max tube current 30 amps pulsed. (From my friend the factory trained engineer)

The tube current must be balanced on the cathode by passing it through the center tap on the cathode transformer , in order to balance the arc discharge over the whole cathode. Otherwise the discharge will etch the cathode at one end causing rapid cathode overheating and failure. So the cathode transformer winding must be able to take both the cathode current and the DC tube current.

While my friend Diane, a physicist loves to measure with an Ohm meter, I for one prefer a clamp on amp meter or a series shunt to measure both the cathode current and cathode Delta T.

Cathode transformers usually have adjustable taps on the primary, and where possible, are constant voltage devices. This is because even with national standards, line voltages vary all over the place, some times on a day to day basis.

My friend Diane, took my writing and expanded it to a more practical conclusion....

I quote:

"Of course, with the high plasma currents, the cathode must also be able to provide the appropriate amount of electrons to generate the ions. At 10A tube current, at least 6 * 10 ^ 19 electrons per second must be produced by the cathode.There are two ways to produce such quantities. The first means increasing the cathode area. This is the route taken with the HeNe laser, and the striking silver cathode cylinder is the largest component in such a tube. In an ion tube, however, the currents are a factor of 1000 higher, so that a sheet metal cathode would really have to be huge.
A hot cathode offers the second way. Shortly after the invention of the light bulb, Edison noticed that the glowing metal thread is surrounded by a dense cloud of electrons in a vacuum. This glowing electrical effect was soon used for the construction of radio tubes. As the temperature rises, exponentially increasing amounts of electrons emerge from a glowing cathode. Unfortunately, the high temperature also slowly evaporates the metal, which we all know too well from the short lifespan of incandescent lamps: at some point the thread breaks at a point that has become thin.
You can help the hot cathodes in other ways. Because of its high melting point, tungsten is suitable for filament, but base metals such as barium give off electrons much more easily than woofram. Tungsten with a layer of barium oxide and barium does not have to glow so much and still gives off a large amount of electrons.

At the time when argon lasers emerged, such high-power cathodes were already available as standard components: in the cathodes of the large transmission tubes for broadcasting. They were adopted almost unchanged for the lasers.


2. Hot cathodes in the laser
Unlike the high vacuum in a transmitter tube, a laser tube is not a particularly hospitable place for an oxide-coated tungsten cathode. Many gas impurities such as oxygen, nitrogen or hydrogen react with the base barium and "poison" the cathode. A more serious problem is the plasma's positive ions, which are attracted to the negative cathode at high speed. An argon ion is around 80,000 times heavier than an electron. When such an ion reaches the surface of the cathode, you can think of it as something like a bowling ball thrown into a bathtub full of peas: there are many peas flying around. Unfortunately not just peas, which correspond to the electrons in this example, because that still supports the production of electrons.It also knocks out the oxide coating atoms and even tungsten atoms. This process is known as sputtering.
The sputtered material is very harmful to the laser. On the one hand, it precipitates in many places where it interferes with the operation of the tube, for example optical components such as Brewster windows or mirrors. Metal deposits in the gas return holes can be blocked then or make the plasma arc prefer to take this route instead of through the main capillary. Secondly, gas is buried under the sputtered material, which of course is then no longer available for lasering and causes the tube to age prematurely.

It is therefore very important that the electron cloud around the cathode is dense enough to intercept and neutralize all incoming ions as early as possible. However, since electron output increases so quickly with temperature, it is so important not to run the cathode too cool. With some lasers with glass bulbs this can be made directly visible. The violet glow of the argon plasma does not go all the way to the surface of the cathode; instead, there is a thin, non-luminous film around the filament. If the cathode heating is reduced, this film becomes thinner and thinner until the violet plasma reaches the filament. I've tried this with a Lasos tube, that's already the case here when the heating voltage only drops from 2.25V to 2.0V!
With a tube with a transverse helix, the film can even be photographed:
http://www.laserfreak.net/forum/viewtop ... 56 # p227031 (2nd picture from above)

But too high a heating temperature damages the tube. Barium is a rather volatile metal that evaporates at high temperatures. It is literally boiled out of the oxide layer, so that the cathode ultimately loses its ability to produce electrons. Here, too, the result is sputtering again in the end.
Consequently, there is an optimal temperature point for an oxide cathode, which is around 1050 degrees Celsius. This is where sputtering and evaporation are in balance.

At very low temperatures of around 600 degrees, tungsten still has a nasty surprise to deliver. Tungsten changes its crystal structure several times when the temperature rises. If it is otherwise rather hard and brittle, it will be soft as butter around 600-700 degrees. At this temperature, a filament can begin to sag, in extreme cases into the beam path. Another problem arises if, as a result of the deformation, neighboring turns of the spiral touch and short-circuit. Deformation and the resulting stresses can even break the filament.
Picture of a knotted cathode:
http://www.laserfreak.net/forum/viewtop ... 24 & t = 51636 (Picture in the 7th answer from me)


3. Delta T of a cathode
Ion tube cathodes have a very strange property. If you have an ammeter in the heating circuit that only measures the heating (alternating) current when heating up a laser, you will notice when the tube is ignited that the heating current suddenly increases by 1.5-3A if the cathode is still healthy. This is called the "Delta T" effect. (It has nothing to do with the fact that the anode direct current flows back through the cathode circuit - only the pure alternating current component is measured.) Can be explained quite simply: as long as the cathode is empty, it is in equilibrium with its electron cloud. Electrons are ejected and picked up again by the cathode. When the discharge ignites, however, the incoming ions capture electrons, so the cathode absorbs less and loses energy. She cools down a tiny bit, the resistance falls (see section 5) and the current increases. If a large number of ions arrive at a high anode current, the capacity of the cathode may no longer be sufficient to neutralize them all. More and more ions come through and hit the cathode, which in turn heats it up more.
The measurement of the Delta T is therefore an important tool to assess the condition of a cathode. With larger lasers, it is easy to see how it gets smaller the further you turn up the anode current. With old and used tubes, you can determine how far you can still load them. Delta T must never be negative (ie the heating current is less than when idling).


4. Processing of cathodes
Oxide cathodes are not so easy to manufacture. The exact process is a manufacturer's secret, but since radio tubes have been around for a long time, the basics are known.
Tungsten is usually not massively processed, but the parts are sintered from powder. The raw cathode is then welded to special contact pins (usually those are made of a high-melting metal such as molybdenum). Then the tungsten filament is coated with a varnish to which a little barium nitrate has been added. After the tube has been welded shut, it is pumped out to a high vacuum (about 10 ^ -6 mbar, so you need a diffusion pump / turbo pump and a cold trap - nothing for newbies!). Since large amounts of air are still trapped in the porous sintered tungsten structure, the cathode is now slowly heated and pumped out more and more. Tungsten burns at a temperature of over 600 degrees when oxygen is present, so you can only go that high when the air has been heated up.
When all air residues are baked out, the cathode is gradually brought to full temperature. For a short time the temperature is increased even further. Now the lacquer on the filament burns with the nitrate, and barium oxide and some metallic barium remain. The next steps in the manufacture of the tube are then dedicated to cleaning the gas filling, the "burning in", and finally the new laser is "squeezed off" by the pumping station.
If air ever enters such a tube again, it will immediately destroy the cathode. If this happens during operation with a hot cathode, that is a worst-case scenario, the tungsten burns irreparably. If it happens with a cold cathode, it is in principle possible to carry out the same steps again, but the base barium will react in the air. Such a cathode will never be really the same again. That is why tubes that end up at one of the professional refillers are filled with argon during the work so that the air is kept away from the cathode.


5. Own measurements on cathodes
Any serious ion laser enthusiast does know the problem: finally bought a tube in the electric bay. But the baby either doesn't have any or only a cryptic combination of letters and numbers on the nameplate. Days and nights of meetings with Aunt Google do not bring any new knowledge. So what to do
There is a way to find out the basic values ​​of a cathode just by taking measurements. The laser tubes from copiers or eye treatment devices usually have simpler tubes that were not necessarily intended for refilling by the manufacturer and have the good old oxide cathodes.
Basically, you then know the expected temperature of just over 1000 degrees and thus the glow color: in daylight a rich orange (just like a ripe orange), in twilight it looks just as golden yellow because of the wider open pupil of the eye. But you should have seen it before, experience is everything here.

Tungsten has another property that makes it its own thermometer. The specific resistance of tungsten changes very strongly with temperature. With a difference of 1000 degrees one not only has to use the well-known linear formula for this, but also add the 2nd order coefficient:

R (T) = R0 * (1 + alpha * T + beta * T ^ 2),

where R (T) is the resistance at the temperature increase of T degrees and R0 is the resistance at room temperature. The constants:

alpha = 4.1 * 10 ^ -3 1 / K, beta = 1.0 * 10 ^ -6 1 / K ^ 2

The term in brackets can be calculated for T = 1000 ° K, it comes to about 6 (six) out. With a temperature increase of 1000 degrees, the resistance of the cathode increases sixfold. That can be measured.

First you measure the cold resistance of the cathode. This is not possible with an ohmmeter because the resistance is almost zero. But you can use Ohm's law and send a precisely defined small current (shouldn't get warm) through it and measure the voltage drop. The former works with a laser diode power supply, and millivolts can be measured with a suitable multimeter. If you have fun with it, you can try it with an ALC60 tube and measure around 20mV with a "diode" current of 1A (varies slightly from tube to tube). Important: measure directly on the tube, otherwise you will measure the voltage drop on the supply wires!
So: 20 MilliOhm resistance of the cathode at room temperature. Let's recalculate the known values ​​briefly: An ALC60 should be heated with 3V / 25A during operation. Again Ohm's law: that's 0.120 ohms, around 6 times as much as the measured 20 milliohms at room temperature. Quod erad demonstrandum.

After measuring the cold resistance you only have to take the value times 6 for an unknown tube, then you know the resistance that the tungsten cathode should have at just over 1000 degrees. The accuracy of the voltage measurement for the cold resistance is of course very important, because the error increases sixfold.
If you now connect a suitable transformer to the cathode and increase the primary side of the transformer step by step using an autotransformer or, if necessary, a dimmer, you can always measure current and voltage (again only measure voltage directly on the tube) until the correct value is reached.
I take measurements like this on ALL tubes. Even with those that come with a power supply. The measurement may not be exactly accurate, but it is always better than flying blind. It is not always said that the transformer, power supply and tube originally belonged together. Some salespeople have little plan, but a lot of business acumen.
The low cold resistance of the cathode also ensures that the transformers hum so murderously when switched on. I wound mine on a 300VA toroidal transformer myself. When an ALC60 is switched on, the heating current initially easily exceeds 50A. Generosity with the transformer core pays off.

[bradstockdale]

Some additional random notes on the 909Z... Some is repeats of what Steve has already provided.

Pinout of my head is as follows... Terminal strip, left to right:

1 Igniter
2 Igniter
3 Magnet
4 Magnet
5 Anode
6 Cathode
7 Cathode

The igniter wants 9 to 15 VDC. For testing, a 9V battery will do the trick. As Steve mentioned, would be far better to have a clean square wave. I forget the polarity at the moment, but will see if I can track down the other part of my notes.

Magnet... I threw together a quick and dirty DC supply with a variac, bridge rectifier, some big caps out of an old fluoroscope I had laying around... Ran about 3 amps into it. Voltage was about 150VDC at the 3A mark from what I recall. Resistance of the magnet was right around 50 ohms.

Cathode... These do indeed have the beefy scientific version of the cathode... I ran mine at about 3.3 VAC volts and it pulled about 25 amps. The transformer has to be center tapped to feed the tube.

Laserbuilder, check your inbox.

Some more details gleaned from a convo with Diane.

- Some of the heads have a piece of coax related to the igniter. If you have one of those, the center conductor is positive, shield is negative, as one would imagine. Mine has a yellow and black wire.

- The 909Z can do pretty impressive power. As Steve pointed out they can run all day at about 2 watts. Overdriven, they can hit 4-5 watts. But lifetime suffers drastically. 20 amps is max somewhat safe current, even if you hear others having pushed them harder.

- In opthamology devices, the cathodes sometimes run at 2.5 volts or so, limiting them to about 300 mW output. But the cathodes when properly fed are capable of better performance (3.3VAC @ 25A or so).

- Tube voltage depends somewhat on the magnet current. Nominal 3A magnet, plasma will run at about 165-170V. The U/I graph is nearly flat. For ignition, though, the tubes like an idle voltage around 300V.


-

[mixedgas]

Bruce specified the magnet on 909 / model eight, at 170-180V and around 3 amps. . He noted that ALC tubes with good gas pressure are tested by the field service engineer by briefly turning off the magnet and seeing if the tube starts. Not a test I would perform on any other brand of laser. Tube voltage without field should rise in such cases from roughly 215 to 280 or more, basically nearly the limit of the rectified line voltage. If it lights with no magnet on the factory supply, well, you know it is good.

In the US, this tube went in HGM Model 8 medical argon, which usually uses a three phase switcher. With rectified three phase 208 or 220 VAC, I'm sure you have just enough voltage to kick the tires and light the fires without the magnet. He has modified Model 8 to run off single phase, it basically involves bypassing a portion of the three phase wiring , moving the flow switch to another phase, and rewiring some interlocks, but no changes to the rectifier or anything else. .

The scientific and medical production lines were separated for the obvious regulatory reasons. So while a HGM model 8 is basically a ALC 909, there can be small differences in construction. HGM Model 8s use the 909 resonator and the medical psu mounted in a single massively heavy casting, it is a two man lift vs one man for the scientific laser.

He did mention a few units were somehow shipped with 2.5 v transformers with specialized mods to the laser head, but none of those were Zeiss...

Again, I need a picture of the tube ends, to tell you what you have. Lexel cathode feedthroughs are flat ceramic disks with long crimped and welded leads, ALC cathode feedthroughs have long ceramic cylinders with a ring terminal termination.

Steve..

[Laserbuilder]

Thanks a lot for such detailed answers. I'll reply when I try powering on this tube.

[mixedgas]

Thanks a lot for such detailed answers. I'll reply when I try powering on this tube.

How are you going to limit/regulate the tube current?

Steve