2mW 543.5nm green He-Ne tube help

I'm planning on buying one of these tubes I found mentioned in this thread: http://laserpointerforums.com/f46/brand-new-2mw-green-hene-543-5nm-gas-laser-tubes-100-a-63093.html (thanks for the heads up, Helios!)

Here are the tubes: NEW 2mW GREEN HELIUM NEON LASER TUBE HeNe Melles Griot | eBay

I posted a couple of replies in the above thread and received some very good advice from icecruncher. Thanks! I just need to try to clarify a couple of things, so figured I'd start a thread here in the hopes that some people with plenty of gas laser experience might be able to offer some further help.

I've been offered a DC input PSU for sale along with the tube; it can be seen at: http://www.mi-lasers.com/stock/eBay/F-27b.jpg . Voltex model F-27-19.

I'm just a little uncertain because the specs in the listing for the tube say that it requires a current draw of 6mA - 7mA, with 6.5mA being ideal. The label on the PSU rates it at 5.5mA, so I'm not sure if it will be ok. Also, I'm unsure about the start voltage requirements. The tube apparently requires >12KV start voltage and the PSU will supply 2300V - 3200V. Would such a PSU be capable of supplying the >12KV start voltage?

Also, in terms of connecting the tube to the PSU, Meredith Instruments can supply a male Alden connector for this. The male Alden connectors I see on their website have coax cable attached. This seems like it could be somewhat difficult to attach to the clips for the tube. How would this be best accomplished?

I'm really quite excited by the prospect of getting this. I have a feeling I'm going to rapidly develop a gas laser addiction. I already want to look in to getting argon lasers, also. I would have done so already if they didn't look so bulky, which could complicate shipping them to Australia!

Cheers,

-Adam

If you contacted MI and they recommended that supply it should be fine. The only thing is you may not get the full 2mW out of it at a lower power. If you want to be sure I'd email them back and ask about it. You'll also need a ballast resistor as noted on the auction page. You could always keep an eye out on fleabay for another supply too.

Yes, I have emailed them back again to confirm that the PSU will indeed be ok, just waiting for their response. I figured I'd see what people here thought, anyway. I had wondered if maybe it will still run, but at a lower output power. There were also the other things about which I'm a little uncertain.

I'll be getting the ballast resistor with the tube.

Thanks for your help.

Cheers,

-Adam

adamsium said:

I'm planning on buying one of these tubes I found mentioned in this thread: http://laserpointerforums.com/f46/brand-new-2mw-green-hene-543-5nm-gas-laser-tubes-100-a-63093.html (thanks for the heads up, Helios!)

Click to expand...

Your welcome!

If MI says your good to go then it will fire up with that PSU. They are a very trusted and knowledgeable supplier. As explained previously though even though its rated at 2mW that doesnt mean it wont laser at 1mW or less.

It should be fine, especially if it has a current adjust pot. I've worked on quite a few HeNe bricks and reverse engineered a couple of them and I've found that the label is more to match a supply to a tube than to detail the actual specs of the supply. I've seen labels with different ratings on supplies that are internally identical or differ only in the value of the current sense resistor. There are 3-4 basic sizes that cover probably 90% of the HeNe bricks out there and as long as you're in the right ballpark you will be fine.

Almost always, the start voltage is generated by a quadrupler and will be 4x the open circuit voltage of the supply, which in this one will be more than 3200V, so the start voltage will likely approach 14kV.

Look for a current adjustment pot, it will be on the end near where the wires come out and may be covered by a sticker. To set the current, connect a multimeter set to read DC milliamps between the *cathode* of the tube and the - wire from the power supply, this side will be at ground potential. When working with a laser head that has an Alden connector, you can rotate and plug it in so that only the + pin is connected and the - pin is hanging free. Connect the meter between the - pin from the head and the green ground wire at the input of an AC powered brick, it will be internally tied to the - output. Power it up, when the laser lights adjust the current to the right ballpark, let it warm up for 20 minutes or so then tweak it spot on. Shut everything down, carefully disconnect the meter and plug it in properly. Be careful, the capacitors in the power supply and the capacitor formed by the laser tube itself will hold a charge for quite a while and getting zapped by it hurts. Been there, done that. Hope this helps.

Thanks so much for your help and advice on this.

I got some further info from MI regarding the PSU and it turns out that it actually does have adjustable current via a pot, in the range of 5mA - 6mA. Here is the spec. sheet for it for reference:

Voltex F-27 Spec Sheet

That sheet is for the F-27-HT model, but, from what I've read, I'm pretty sure the 'HT' designation simply indicates that it is the 'high temperature' version for use in higher temperature operating environments, but otherwise virtually identical in operation.

Also, Chad said he will preset the current for me when testing prior to shipping, so that will sort out that. It will also leave no uncertainty as to whether or not it will run the tube. He also said that the current draw is only about 850mA, so a 1A supply will power it (the HV PSU) just fine.

I've actually also just ordered a few tubes (small, red ones) + PSU from Sam, so I can't wait for them to come. Sam was absolutely fantastic to deal with!