Liconix 4420, 4425 or 4430 Helium-cadmium laser tubes - reviving process

[shrad]

Hi all

I had the opportunity to get my hands on 3 liconix 44XX tubes (two 4430 and a 4420 if I recall, the stickers are not in front of me)

I'm in the process of designing a power supply for these babies, and have read sam's notes attentively to draw the process

I wanted to ask here is there was anyone with a liconix laser tube manual, power supply manual, schematic or anything else which could help me reviving them

I'll put pics here as soon as I'm home this evening, and try to get plasma light for your eyes

So if you have ideas, suggestions or recommandations, please tell, I'll write my progress here during the power supply design and tube rejuvenation

They have 3900 hrs, 4500 hrs and 6000 hrs, so at least two of them should run fine some hundred hours, the tird may be for spare parts but I'll experiment a way of cadmium remelt-and-take-back-to-the-reservoir inspired by Steve's suggestion of reverse transport via HeNe power supply

[mixedgas]

OTE]

First of all do not inadvertantly activate the helium heaters. To control the helium pressure in the tube, heat driven diffusion across a glass membrane is used to add helium to the discharge.

Liconix used a cathode that is for all practical purposes, the beefed up coiled cathode from a 40 watt T12 fluorescent tube. So get the cathode to a 950-1170 degree color temperature, but surely avoid the 700-800' range to avoid sagging.

cataphoresis is proportional to current, the hene may not drag much CD back to the source.

If there are metal tabs near the brewsters, they are shutters for keeping Cd off the windows, and activated by magnets.

Are these sealed mirror? If not, you can adjust the currents and temperatures by passing the beam from a working hecad down the bore and measuring single pass gain with a chopper wheel and ac coupled photodiode.

now you know what I do...

Read US patents and papers by Shing Chung Wang at xerox labs and Silfvast... Xerox did most of the commercial HeCad development that became melles/liconix...

Liconix was bought by Melles, I'd suggest a email to Amir in Gas Lasers with models and serials, tell your a hobbyist and see what reply you get...

Steve

[shrad]

thanks Steve, I'll investigate!

could you please explain me a bit about those colors? I never had the opportunity to admire a neon electrode glowing, so I couldn't tell

the actual tubes have a row of say 12 magnets glued to one of the carbon rods of the resonator, they have a cadmium condensation receptacle at each end, are external optics, etc... (you'll see by the tube picture)

I think the cathodes are heatable and the reverse powering could do the trick to rejuvenate them in the case it would be needed, and I have a homemade "HeNe psu" which will give several kV at a nice 50mA.. I'm planning to design my PSU around it, or a switching design (a pair of old computer SMPS transformers with decent mosfets should do the trick)

I have made pictures of the tubes:

Attachment 15891Attachment 15893
Attachment 15892Attachment 15894

[mixedgas]

See pic:

You have a center anode dual cathode tube.. Ie split power supplies. With "cold" neon style cathodes...
The Cd pressure is regulated by discharge current and probably by pieces of stiff card in the lid that restrict airflow. See if there are tan colored cards stuck in the lid. If not, dont panic, I imagine at some point they stopped doing that. No sense even bothering Melles about this, its quite a few generations back.. They may have some data... I have a manual for one generation back, not that it tells you much.. I think the two torroids just after each cathode are your Cd resivoirs. I have no idea what the extra (heater?) thing around the anode does. I think the orange heater around the gas resivor is to keep the Cd from acting as a getter and burying gas in the huge surface area of the resivoir. I do know Cd likes to go where it is cold and condense, even if this means blocking its own anode. You certainly DO NOT have a remelt heaer...... I cant tell if the extra wires around the anode lead to more heaters.

BTW, hexavalent cadmium compounds are very toxic and nasty carcinogens. If you break a tube and get cut... It could have repercussions... Dont worry too much, millions of refridgerators and stoves/ovens had Cd plated grills in the US for decades before they figured that one out...

I had one of the generation before this,that only had one cathode, but a person I mistakenly trusted to ship it.......... So I never got to see it lase...

Steve

HESCHRADCAD1..bmp

[mixedgas]

The magnets are for Zeeman splitting like on a hene. I'm guessing they probably are trying to force the tube to favor one Cd isotope in this case. HeCad is subject to gain loss and noise from isotope broadening, so eventually they learned to use single isotopes, but I have no idea if this tube has expensive single isotope cadmium.

This would be a good time to read every hecad patent out there, and any of Silfvast's papers... I think Daedal has one of these or similar with a working psu...

Were it not for the isotope and noise issues, these things would have eventually became nearly as cheap as external mirror henes....


Steve

[shrad]

Hi Steve,

thanks for your interest here!

I know the Cd reservoir is just under the anode, with its heater and thermistances covered by the asbestos layer (that's the reason I was assuming it would be possible to put a heater band around the cathode getter reservoirs to remelt Cadmium and transport it back to the anode, while keeping the Cadmium reservoir to a lower temperature allowing the Cd vapor to condense)

I'll have a read at the patents I can find, and perhaps ask the guy who gave me those heads if he still has his PSU manual and schematics (he told me he could have a look)

Basically, the heads I have are similar as the 4410 heads (single cathode) which may be like the one you had... if so, if you have some characteristics to give me about heaters voltages, thermistance values and topology (is it differential heat/pressure like for omni tubes?), I could try to start a tube and check if they are bad or not

In any case, shooting rectified HVDC didn't show any plasma at all (should it have?)

I'll keep you informed about the progress, it might be slow as I have pspice models to design and debug, and work is quite intensive these days for me

[mixedgas]

Cataphoresis moves cadmium from cathode to anode, not anode to cathode. The anode heater keeps the tube from clogging with Cd...

Steve

[shrad]

thanks Steve,

I'll try to investigate on the pins of the tube and draw a pinout

do you have any clue on a basic test sequence for lasing? I'd like to test them, even if it is during less than one minute

also, with what you said about the anode heater, I can't figure where the cadmium heater is for now

I'll get back with more information

[mixedgas]

A hene supply with a ballast resistor of say 45Kohms is fine for lighting the tubes for testing.

You should be aware that under proper operating conditions it can take 10-20 minutes to get enough Cd pressure to start lasing.

Steve