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Thread: ALC68 PSU schematics

  1. #11
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    Yes, it was Jim, but he had the original ALC PSU so it's not the one I have unfortunately.

  2. #12
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    Quote Originally Posted by danielbriggs View Post
    Possibly Jim / Smogthemog
    I was going to say it was Smog, but I wasn't certain.

    Quote Originally Posted by NobleGas View Post
    Yes, it was Jim
    Cool! So Daniel and I did remember correctly!

    he had the original ALC PSU so it's not the one I have unfortunately.
    I thought you said you did have an original ALC PSU, but that someone had modified it (following a failure of some kind) and you were trying to re-build it back to stock.?. If you don't have an original, what do you have? (Just curious)

    For what it's worth, the medical HGM5 power supply will also fire that tube. So if you can find one of those on the surplus market, that's another option.

    I had an HGM5 years ago, and although the tube was dead the PSU was fine, so I ended up using it to power a smaller ALC 900 series air-cooled tube for a while. (Can't remember the specific tube model, but I remember it was something of a one-off design...) But anyway, those HGM supplies are pretty decent if you can find one.

    Adam

  3. #13
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    My bad, I may have forgotten to mention that when I popped the cover of the ALC PSU, all that was in it was a transformer, a bridge rectifier, a relay , 2 big caps and 3 500W resistors on heatsinks; clearly beyond saving!
    I put an offer on 1 of two EIL-4000s from a company down the road and got it for a reasonable price, so I'm now setting that up for the ALC-68.
    I'll keep my eye out for the HGM units as I can find a use for another similar PSU.

  4. #14
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    What it sounds like someone did is run the tube off raw DC with a series limiting resistor.
    OK in theory, in practice not something I like to do.


    Closed loop current feedback or light feedback prevents high audio frequency plasma oscillations that can wreck havoc on the tube internals.

    With a resistor limiter, if the line voltage goes up, the tube current rises up. If you have a bad low line voltage day, you have no show. Plus in clubs with shoddy wiring, your pulling down your cathode transformer voltage.

    Unless you have switchable arrays of resistors, you get one beam power, that is max power, and if you do graphics with one of these you will see power line fluctuations in your image.

    It works, but unless the resistor value is adjustable, it is very rough on the tube... Regulated tube current phenomenally improves tube lifetime.

    The power supply filter caps are VERY critical. I once had an employer say that keeping the precision experiment running for 24 hours to get data with the laser lit balls to the wall was more important for me shutting down for an hour to replace the blown PSU filter caps. There was measurable 15-20% 60 Hz modulation on the tube current, instead of nearly zero current modulation with a good active three phase psu. I warned him, and he was POed and ordered me to keep the data collection going. Next day I was doing the paperwork to order a new tube for a Lexel 95.
    Thus an active PSU is far less risky then a resistor based PSU. BTW, If it were single phase, that modulation would increase at least 30 more percent if a cap failed.

    In a resistor based power supply, with the filter caps right across an unfiltered line voltage, the caps have a very short lifetime.

    Besides, its a worse room heater then normal. Example: US 120VAC power line with a 15 amp household breaker = 1.8 Kilowatts available, roughly.. Tube voltage for a Argon 60X, overdriven to the max, would be 106 volts at 9 or 10 amps, (1100 watts) so your resistor has to dissipate available power line watts minus actual tube watts. So least 500=600 watts or more into the air..

    Steve
    Last edited by mixedgas; 05-03-2019 at 18:56.
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  5. #15
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    I figured that's what he'd done, hence why I bought a replacement PSU.
    Cheers, Martin.

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