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Nice looking Helium Cadmium laser on ebay






diachi

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Coherent said:
I found this HeCd laser on ebay and it looks good other than the 7200 hours.  PSU/cables are included and the seller guarantees that it will work.  Apparently it has 2 filters that would need to be removed to get full output.
http://cgi.ebay.com/OMNICHROME-SERI...5|66:2|65:12|39:1|240:1318|301:1|293:1|294:50


The filters probably filter out 442/325 ( I think thats the UV line ) .

Anyway, looks like a good deal, but the only problem is the fact that it is REALLY fragile. If you have ever seen a HeCd laser tube, you'd realize why they always break in shipping :(
 
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7200 will be dead as a doornail.

These only live about 5000, ONLY because the cadmium depletes. You would think on a design like this, where there really isn't any 'wear' components in the tube, that the manufacturers would have put in like twice as much cadmium. The stuff is cheap!! Oh well...

I'd stay away from this one.

What REALLY gets me... is why did they buy such a big laser if they were just going to attenuate the power down to class 3A levels? Doesn't make much sense  :-?
 
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Cyparagon said:
Can't you just run it lower?

Yeah you can adjust the Cd heater, but it's a pot on a board inside, not labeled, so most people don't really know how to turn it down.

One thing to note, is that since this is an omnichrome system, they have an 'idle' setting where the Cd heater turns off and the tube current/volts go down. I'm not sure if the hour meter still runs at this stage, but if it does and it was idled for a long time, the laser may still have some life in it, but it's a big gamble.
 

diachi

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Cyparagon said:
I take it you can't really refill it?

It would probably be the same kind of process as refilling an argon laser. You would need to clean out the tube, and get all the metal out, make sure there is no air left in it, then refill it and add the cadmium and then seal and bake in. It would be expensive.

-Adam
 
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yeah diachi covered it. No way to refill the cadmium without a full tube overhaul. The GOOD thing is that these aren't QUITE as picky as argon lasers go (as far I know) when it comes to gas purity, pressure, etc etc.

As long as you're taking apart an existing head and not trying to build your own, I'm sure it can be done. For a quick and dirty fix, which may or may not work, one would probably break/melt off the Cd reservoir, add in more cadmium, melt/epoxy it back on. Find a good place on the tube to melt a fill stem onto, pump the tube down to about the right helium pressure and seal it off.

The one thing I'm not sure of is how to refill the helium reservoir... I think it has a bit more pressure than the rest of the tube. But, there is a section of tube on the helium reservoir which is covered in silicone banding, so there may actually be a little valve in there, so you can have more helium pressure in that part of the tube than anywhere else.

Then just turn the key and see what happens. The good thing, at least with liconix lasers, is they sense tube voltage and add more helium accordingly. If it's too low, it will keep heating the He reservoir until the He pressure is where it should be. Also, there are sensors for the actual Cd temp (versus the set temp) as well, so your Cd partial pressure will be exactly controlled.

So, it would be incredibly difficult, but worth trying; especially if you have a dead tube that is Cd depleted. Trying to build one from scratch, on the other hand, would be a pain in the ass... haha.  :cool:

Picture of the tube, so you guys can get a better idea of what you'd be working with. Note: this is a liconix tube, which is vastly different from an omnichrome tube. Omni's use a heated cathode, like an argon, and basically have a 'straight' tube design. You can tell from this picture that liconix tubes are definitely not just a straight tube. There are things shooting off everywhere  ;D


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