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Thread: HGM won't lase

  1. #1
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    Default HGM won't lase

    So I fired it up this evening to find it won't lase. It fires a few times and then sustains an arc, but it's on the side of the tube... only one side of the tube is glowing. is the arc sustaining itself through a return hole? I haven't made any changes to the system since it last worked, nor have I moved it, but it has been a month or so since I've turned it on. Could it be a magnet issue?

    Any insight is appreciated

  2. #2
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    Now, with my *very* limited knowledge of the HGM tubes, it does sound like a magnet issue. When a gas becomes ionized it is magnetic, and I believe it is the magnet's job to keep the arc down the center of the bore.

    I know that doesn't help much... hopefully someone else will chime in soon. My HGM5 is in the mail on it's way to me right now, so I'm a bit curious about how to solve this issue.

  3. #3
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    I had a problem of return path ionisation in a Spinnaker. I reduced the prior to start voltage on the tube and it started to ionise properly.
    Return hole firing is dangerous as it heats ceramic boundaries not designed to, also promotes further starting that wrong way.
    Which HGM tube is that ?
    Piotr.K

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    model 5? I'm not sure what you mean.

    Yeah, I figured it was dangerous and hence didn't leave it on more than a few seconds. I tested the voltage and I measured ~280V across the tube . It usually runs at 180V or so if I remember correctly. How would I go about reducing the voltage?

    The starting voltage before the arc is established is ~320V currently.
    Last edited by Xytrell; 10-17-2008 at 21:43.

  5. #5
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    Cool

    High voltage is a symptom of the tube lighting down the gas return. Not good.

    Could be a magnet issue - could be a couple other things too. Best bet is to contact Steve Roberts (MixedGas) and ask his advice.

    I have an HGM5, but what I know about them is barely enough to fill a thimble.

    On the other hand, Steve practically wrote the entire Ion Laser section of Sam's Laser FAQ himself, so I'm sure he's got an answer for you.

    Piotr.k;

    The HGM5 tube looks almost exactly like the old American Laser Corp. 68B tube. The main difference is that the brewster stems are a little shorter. (And that little bit of information also came from Steve!)

    Adam

  6. #6
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    Start with the Hour meter, ie how many hours are on the tube in question?

    What current did you run it at? Did you have current control? was the light feedback loop working or disabled?

    Did it receive any large mechanical shocks lately? Ie enough to knock off a return bore guard inside the tube? Any rattles in the tube when moved?

    180V at how much current? Any flickering when running? How much green to blue ratio in the beam?

    The model 5 magnets are wound with 12 guage wire, its most likely not a magnet unless the wiring is corroded.

    Steve Roberts
    Last edited by mixedgas; 10-19-2008 at 10:32.

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    If it has an hour meter, I haven't found it. It is configured for current control with min and max being 7 and 34 A respectively. It has a larger bore and is capable of up to and perhaps above 4W. I usually ran it around 1.5 to 2W. I have a much larger cooling system, so cooling is not an issue (except for the anode). There was no feedback loop included with my system, I have only the stock PSU and tube. It hadn't moved an inch from the last time it worked properly. There was no flickering at all, and the ratio between all the 7 lines contained nothing anomalous as far as I can tell. I also do not hear anything rattling when I move it slightly.

    It's like it just gave up

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    Sorry that this is a bit off topic, but with the HGM5 tubes, how can one tell if he has the 'larger bore' model?

  9. #9
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    Smile

    As far as I know, they're all "Large Bore" tubes. That's how they can get 3 watts out of such a short tube. (I've heard that some of them would give 5 watts + for short periods when they were brand new!)

    Adam

  10. #10
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    Really? That's not what Chris from heruur told me.

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