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Thread: Lexel 85 questions

  1. #1
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    Default Lexel 85 questions

    I bought Lexel 85 with PSU, probably NOS or very low hours, but untested. What I should test before start it to avoid any damage?
    Also I think about making a heat exchanger for it to avoid using tap water. Have anyone done this before?
    And maybe someone have a manual for it?

  2. #2
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    First thing I'd do is run some CLR thru the water system, check the cathode to make sure it's intact, check for shorts in the passbank and be sure to set the buck/boost transformer taps per the instructions in the manual. Once all that checks out I'd fire it up. If you're lucky, it will still be in alignment, if not that part will take a significant amount of time depending on how experienced you are with aligning ions.

    PM me your email address for the manual.

    The 85 is an awesome ion. Built like a tank. One of mine was built in 1977 and still running great today.

  3. #3
    mixedgas's Avatar
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    Some random thoughts:
    -
    Check all the fuses.
    -

    First thing, gently resocket and straighten the transistors on the current control card.
    -
    Keep the current down to 13 amps max until you have some hours on it. Make sure the cathode switch is tapped according to the chart, and make sure the transformer is tapped accordingly. Be sure to power down the system when making cathode tap changes.
    -
    Lifetime is best if the tube is ran in the middle of its current range, too low (4A) is hard on the tube, as is too high.

    When you start, start in current mode, and turn the knob to three quarters of its maximum rotation, then back off a bit. This is to ensure enough drive to the passbank to close the control loop. It also ensures you have enough current to quickly form a cathode spot.
    -
    Make sure the REG VOLTS reading is in the green and more then 3 volts. Otherwise your miss-tapped. REG volts will go down as tube current goes up. This is normal. Quick explanation, when at low current, the passbank is dissapating more power then at high current.
    -
    If the plasma starts, and you do not have current control after a few seconds, shut down.
    If you put it in light mode and it slams to full current, but you have no regulation, shut down.
    If you start it and you hear more then a very loud hum, or it oscillates, shut down.
    (Loud hum is relative, some of these really sing at 60-120 Hz)
    If you put it in light mode and it is mis-aligned, it will shoot the tube to the internal upper limit, which over time is hard on the tube.
    +
    THis PSU is "Dumb", it is a collection of a few op-amps and relays. It won't warn you if your abusing it and the overcurrent limit transistor is burned out. You have to monitor the AC test points during initial setup.
    -
    Dont be surprised if it does not lase. Usually just the rear mirror will be out. Mark the rear horizontal and vertical knob location with a pencil before starting. Leave the front alone.
    -
    You should hear a solid but soft click from the flow switch when you have both the pressure and flow high enough. You should hear another softer click when it drops out. Make sure the flow switch is working before you start for the first time.
    -

    Only other to watch is to back off the brewster stem covers if you rock and sweep the rear plate to find lasing.
    -
    The brewster stem covers may be pretty much stuck on at this point, if that is the case, I have a few ways of loosening them up.
    -
    If you give me the model number on the magnet, I'll have a factory tube spec sheet I can scan in. I'll also scan you the Lexel Passbank test guide. I'd check the passbank transistors for shorts before starting up, unless you know its in working condition. If you need 2N6259s, let me know as I have more of them then I will ever need.
    -
    The passbank insulators are Beryllium Oxide. It is toxic if ground to a fine powder and inhaled, so use caution when changing transistors. If they break, spraying with water and disposing in a plastic bag, then washing your hands is enough of a precaution. You really have to work at it to make dust. As in grind with a Dremel tool.
    -

    Enjoy, Be careful with the beam, and the ghost beams from the Brewsters as well as the very high voltage and current inside the PSU.
    -
    Cambridge-Lexel usually will send you a PDF manual if you email them, and perhaps a test sheet for your tube if you have the serial number which is on the magent in the head.
    -
    Dz has an alignment video on Youtube some place that is worth watching.

    Steve
    Last edited by mixedgas; 12-06-2015 at 16:18.
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  4. #4
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    Thanks Steve, Thanks DZ! Today I had some time to work on it. So, this laser was built in april 1975, tube serial is 375Ar p/n 108 - 040 - 00, with zero on hours meter. The power supply is different from standard, it has no key, no light meter, no REG volts switch, no autostart switch. It has only Amps meter, mains switch, fuse/interlock/power indicators and light/current control knobs. PSU and head is very clean, and there is no leaks anywhere. Interlocks and flow with are working. But, it's failed to start.

    When I press the POWER ON button, PSU clicks and turn on the cathode heater (mains current rises to 9 Amps at 220V, then slowly go down to 6-7 Amps), I hear a quiet 50Hz hum, then after 15 or so second ready lamp turns on. When I press the start button, I hear loud buzzing sound from ignitor, and that's all. No plasma flashes, even when ignitor working. I targeted a camera to the bore, and there is nothing happens when ignitor working. Seems to be a tube problem? What to check from this point?

    Also, there are few more strange things: all interlocks are not defeatable, no emission indicator, no warning labels.
    And the ethalon heater led blinking, does it mean that ethalon installed? There are some parts with numbers 310 and 350 near HR.

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  5. #5
    mixedgas's Avatar
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    Well, it has an Etalon card in the head. Take me a pic with the igniter cover off please.

    Steve
    Qui habet Christos, habet Vitam!
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  6. #6
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    I'm interested in any pre-1975 lasers. If this one can't be brought back to life, please let me know. Where are you located?

  7. #7
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    Eidetic, I'm in Moscow, Russia. Half of the planet from you

  8. #8
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    There are some photos of igniter. This black cylinder in acrylic tube on the upper side of igniter seems to be 30K 10W resistor if I'm understand schematics right. And it's shorted and seems to be burnt. I think I can replace it with series of resistors in shrink tube.

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