HeNe Help... Part 2

So I just picked up a GreeNe from the eBay listing on the eBay thread. It's a Coherent 31-2772-000 manufactured in May 2001 with a Coherent PSU 31-2801-000. PSU input is 12VDC, Wmax=28, Hz: N/A, Output 2.5-3.1 KVDC, mA=6.5. Ground=black, +12VDC=red, TTL=yellow, and CDRH=violet. So now, I'm using my HitLights main 110VAC to 12VDC 2A output adapter (which is soldered to my red HeNe PSU but that shouldn't be an issue I think) to connect positive to the red lead and negative to the black&yellow leads.

The delay of 5 seconds is on (haven't cut the violet lead yet), and then it ouputs a "pulsed" green beam. I believe that's because it's actually sputtering, but it's a consistent and pretty even "pulse", pretty fast too, probably around 20Hz or more. Any ideas what's going on?

The PSU doesn't mention the input amperage requirements; is 2A not enough?

Here are my tube measurements: ~43.5mm diameter, ~51.0mm length

I do intend to bare tube this guy, perhaps I'll get lucky like last time and the bare tube operation actually resolves the PSU issues? oh and btw, a quick check shows that almost all of the spots are set screws or some other kind of hard plastic filling, not rubber :thinking:

Thanks guys :beer:

it might be the PSU. I use that same PSU for my green tubes and I found it needed a little over 2A to be happy. When using a 2A supply it was pulling the full 2A and emitting a high pitched whine. Using a 5A supply the whine stopped but it was pulling 2.12A.

My yellow head came with that PSU as well but I've only ran it off the 5A supply so I don't know if it's drawing more than 2A like the other one. I can measure its draw too if you want.

yeah it sounds like its just not getting enough current. that's usually the cause of sputtering. All the henes I've seen run CW as pulses are generally bad for the tube.

I'd give you DC current readings, but I have a lab supply and its very efficient, only drawing about .4 amps and out putting at 6.5mA

I agree with LKP, if the PSU is making noise, and it might not be getting all the current it needs, that would be my guess. these are not diodes. they shouldn't sputter or pulse. they are continuous wave. continuous lase. I would find another greater current source and seek a second opinion. if it does the same thing with greater input current, then maybe it IS the PSU.

LKP yes that would be great, thanks :beer:

I'll hook up my GreeNe to a lab power supply tomorrow at school, I think our school lab PSU's can get up to 12A outputs but if it is just a current issue, a 5A wallwart should solve the problem, right?

Ok I just did a quick and dity test and came up with some interesting results. I used my mastech 30V 3A bench supply set to 12.2V (more on that below) and 3A to power both supplies. I used my green HeNe head for both tests. I also connected my Fluke 87v inline to see how accurate the PSU's display was.

The first PSU tested was the one I got with my 594 head. The bench supply showed a draw of 1.93A. The 87v settled in at 1.936A.

Next I swapped in the PSU that came with the green head. The bench supply showed 1.94A and the 87v 1.947A which has me baffled. I've measured that PSU's draw at 2.12-2.13A several times (and posted a pic showing so in a there here somewhere). I know I measured that on my old el cheapo no-name DMM but I doubt it was off that much. Now I'm going to have to dig out the 2A supply that caused the one PSU to whine as well as the external HD supply that I measured the 2.12A from and remeasure both with the 87v.

Vary your supply voltage and you'll see the current will change. The constant current is on the output, not the input.

That's what I was thinking. I forgot to add in my previous post I must have hit the adjustment knob because I had it set to 12v exactly when i was using it to power another PSU the other day. I don't know if the extra a .2v is enough to make the input current drop by .15A. I'll have to do some more testing but that'll have to wait until later. Furnace crapped out yesterday and I have to go clean out some stuff so the repair guy can do his thing.

I'd agree, not enough current. definitely should not be pulsing. I am confused by your tube measurments... is it reall just 51mm long? 5cm? I would imagine it would not lase at that length.

I think he meant cm.... If so it's a 20" tube. Which sounds correct. I've seen one of these, and they're pretty big. My yellow is 18". The rare colors are all longer or else they don't create enough gain to get a decent output. Green is ironically the hardest to get out of a HeNe....

I just noticed that head is the same model as mine and it measures 51cm/20in long. IIRC my bare green tube is 19" which would leave an inch or so in the back of the housing for the wiring and ballast.


Unless that tube is sadly EOL I can almost guarantee the problem is not enough input current to the PSU especially after the issue I had with a 2A supply. I'd guess that it just can't put out the full 2A when fully loaded.

Well you lose some from lack of efficiency in use. Generally subtract a little off its rating. You shouldn't run a ps at full power if avoidable.

ultimatekaiser said:

I think he meant cm.... If so it's a 20" tube. Which sounds correct. I've seen one of these, and they're pretty big. My yellow is 18". The rare colors are all longer or else they don't create enough gain to get a decent output. Green is ironically the hardest to get out of a HeNe....

Click to expand...

Yeah thats what i assumed. a 20 inch tube sounds SWEET. ahhh. i can't get over that. anyways, i didn't know that green was the hardest i thought yellow would be, i've seen more greens available than yellow.

Yeah sorry 51cm, and the laser fired up nicely with the lab PSU today time to find myself a wallwart

Oh and, I just removed the rubber and set screws. Six places per rotation, two rotations on the tube, alternating rubber and set screws. The set screws are very hard plastic; a knife and some force got the indents I needed

Glad it fired up with a beefier supply.

This is the supply I normally use with my green HeNe.

Amazon.com: 110v AC to DC 12v Power Supply with 4pin Molex (5000mA): Electronics

I rigged up a handy adapter cable with a few dollars in parts from newegg as shown here.

http://laserpointerforums.com/f43/powering-12v-hene-psu-update-adapter-built-58243.html#post830669

The supply shown in that pic is the one the HeNe PSU didn't like which is why I ordered the 5A version.

SKeeZ said:

Yeah thats what i assumed. a 20 inch tube sounds SWEET. ahhh. i can't get over that. anyways, i didn't know that green was the hardest i thought yellow would be, i've seen more greens available than yellow.

Click to expand...

well, its mostly based on supply and demand really, and its based on the coated refraction indices of the mirrors....as well as the ratio of the gasses.

its easy to get all the lines...but its difficult to get certain lines to have a true lasing action. Red 632.8nm and the 3.3um wider lines I believe and are the easiest to create lasing action from. orange, yellow, and green are harder to produce. but green 543 is I believe one of the smaller lines and requires the most work to create. hence why most of the greens you see typically don't output very much despite their size. a 20" tube might output 1.5-2mW vs an orange 612 or a 594 outputting around 4-5mW at 18". the equivalent of that in red might be closer to 15mW...but demand for anything other than red or green is pretty low. from what I understand that's what killed the orange wavelength. They're no longer mass produced and are quite rare, as most applications for 612 can be done equal or better with 594.1nm cavities.... 594s are almost as rare as these applications are few.