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Thread: Problems lighting a small Spectra-Physics Argon Multi-line..

  1. #1
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    Default Problems lighting a small Spectra-Physics Argon Multi-line..

    Hey Everyone...

    Got a problem with an air-cooled argon; hoping some of you can give me a little advice.

    I've got an SP-261B, 110V Argon power supply hooked to an SP-163A head. I removed the working single line (488nm) tube from the head, and installed a multi-line head that I bought off E-bay. (The single line tube was a model 092, and this multi-line tube is a model 093, but it's otherwise identical in size and shape.)

    I had to screw on a connection to one of the cooling fins at the nose so I could hook up the anode wire. Otherwise, everything hooked up the same as the 488nm single line tube I pulled out.

    I fired up the power supply, and.... Shit.

    All I get is a flash of light when the starting pulse hits. The tube doesn't stay lit. The power supply keeps trying to start the tube, but after 3 or 4 flashes I usually turn the key back to standby. (I remember reading in the FAQ that it's not good for either the tube or the power supply to just let the ignitor keep pulsing the tube like that.) I had the power supply in current control mode with the current dialed up wide open. I tried it 5 or 6 times this morning with no luck.

    So now what? I'm assuming that either I've got a tube that is near end-of-life and is thus low pressure, or else it's a tube that has been sitting on a shelf for a long time and is high pressure due to outgassing. Either way it's not starting. So what's my next move?

    Adam

  2. #2
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    Default

    Hi,
    Make sure the fillament is drawing current and is NOT open circuit. Try the laser on a variac and turn DOWN the power supple line voltage by 5 volts. If that does not work try turning the line voltage up by 5 volts. Once the tube starts don't let it run at too high a current on the variac, say 6A for awhile. After cool down it may act fine. Some SP heads have different # of spark gaps in the head; it could need more gap or less...I have had this problem before with a tube in good condition...dam gas lasers! If all else fails e mail sam Goldwasser at Sam's Laser FAQ. Phil
    Phil Bergeron( AKA 142laser)

  3. #3
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    Default Re: Argon tube problems

    Phil;

    Thanks for the tips. I'll give it a try later this week and let you know what happens.

    I agree - gas lasers are a pain. But they're cheaper (usually) than comperable power in a solid state design, so as long as I'm on a limited budget I think I'll have gas lasers in my collection.

    I've already checked continuity across the filament, and it's OK. I haven't checked the filament current flow though... I'm kinda gun shy about hooking anything up to the tube and them powering it up. Don't want that high voltage starting pulse to find it's way into my DVM!

    As an example of what I'm talking about - Yesterday I loosened the mounting sled for the tube so it would be easier to get at the terminal strip. But when I powered the head up, the starting pulse arced from the anode end of the tube to ground via the head of the mounting screw on the sled that was sticking up. Flash! Pow! Yikes! Scared the hell out of me. (I hate high voltage...)

    I got the screws tightened down now, and it's not arcing anymore, but now the old single line tube (the one that was working before) is just flickering. I'm wondering if the arcing screwed up the ignition circuit. Sigh... More experiments later tonight or tomorrow I guess. (Now that I think of it though, it may have simply been a bad connection at the anode end that couldn't handle the full 6-10 amps of tube current... I mean , if the ignitor was shot the tube wouldn't light at all... Eh, I dunno - need to play some more to be sure.)

    Adam

  4. #4
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    Default Re: Argon tube problems

    [quote="Buffo"]

    I've already checked continuity across the filament, and it's OK. I haven't checked the filament current flow though... I'm kinda gun shy about hooking anything up to the tube and them powering it up. Don't want that high voltage starting pulse to find it's way into my DVM!
    [/quote="Buffo"]

    Let me start by saying this: I have done some absolutely dumb shit with my Fluke 179. Were talking dumb stuff beyond the realm of acceptable sanity.

    It survived all of it though, only blew one 10A fuse when I dead shorted the 50A circuit breaker

    It also survived *and* displayed the 470V starting pulses of on the busted argons I have here. So yea, very impressive tool. I should give them an award of some kind.

    Also: There is no current flowing *through* the tube until the plasma is established, even then a low idle of 5A wont hurt the DVM I imagine, the leads are usually electrically behind some serious resistors. The cathode heater is another ball game entirely. 2.8v at 28A all the time... not something to sneeze at.

  5. #5
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    Oh, crap. Arcs to ground often blow parts in the supply. Our engineer blew up my power supply when making a small adjustment once with a screwdriver short to ground. POW...supply needed a few parts. If you can not figure it out with the schematics I suggest Sam Goldwasser for the repair. He is reasonable...just send him the whole laser. See the Sam's laser FAQ site...he has lasers for sale and does repairs too! Good luck.
    Phil Bergeron( AKA 142laser)

  6. #6
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    Default Argon woes...

    Hey Phil!

    Thanks for the advice. I contacted Sam about the problem, and he's considering it. (Hope I'm not imposing on him!)

    Sam did some testing for me about a year ago on some HeNe tubes I had. Out of like a dozen tubes there were something like 3 that were viable. I let him keep the rest for the mirrors. He did manage to get one of the Green HeNe tubes to lase, but it's only making like 10 microwatts or something! I didn't have a use for it so I told him to keep that one too. He says he still plays with it once in a while trying to get it to work better.

    In any event, he spent a whole lot of time troubleshooting the pile of crap I had, and was able to separate the good from the bad. Honestly at the time I felt kinda guilty that he spent so much time on it. (He woudn't take money, so I sent him some gift cards for Outback and Applebees instead...)

    Any way you slice it though, he's a hell of a guy... He even said that if he couldn't help me with this problem he'd recommend someone that might. I'll keep you posted on what happens.

    Spec;

    I'm not worried about the voltage (or the current) from the pass bank, I'm worried about the 10KV (or higher) ignition pulse! I've read that several people have fried their DVM's (or oscilloscopes, for that matter) when the high voltage from the ignitor hits the meter. I don't know enough about the SP-261B power supply to know where (exactly) to connect my DVM so I can look at tube voltage (or current) without being exposed to the HV of the ignitor circuit.

    Besides, most of my DVM's are pretty cheap to begin with. (Though I do have one nice one - a Sperry I think - that might have a chance of holding up. It's a clamp-on style, but it's built like a tank.) For sure the two that I bought at Radio Shack aren't going to survive though!

    You've got a Fluke, which is built like a friggin' battleship. I know - we used to have them on the boat when I was in the Navy. They could survive a four-foot fall off a bench onto a metal deck with no ill effects. Tough stuff... (I once saw a Fluke take a hit of 3200 volts DC from a Geiger-Mueller tube on a scaler in the nucleonics lab. Dumb ass ET didn't have the HV probe on, and when he got the test clip close to the tube it arced to the probe and the meter over-ranged. But when he powered it off and back on it was just fine!)

    Adam

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