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Thread: Melles Griot Omnichrome Series 74 HeCd Helium Cadmium high voltage coil

  1. #11
    Join Date
    Mar 2015
    Location
    Cambridgeshire, England
    Posts
    333

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    You're a bit late to the game Phil, I put one in the post last week

  2. #12

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    I haven't heard back from you Phil, did you get my p.m.?

  3. #13

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    Hi Phil

    I didn't hear back from you. After removing that ballast resistor, I found it has two high voltage leads and a bleed resister to ground on a third white lead. The one Noble Gas shipped looks like it has only one. I'm happy to keep the first one sent from Noble Gas (Not his fault and I said I would take it to try it but without the 2nd high voltage lead things may not work), I'll just put it in my spare parts. If you will list the one you have on Ebay, with a buy it now and send me a link when it's convenient for you I will promptly pay for it. I'm In IA. 51503 so no worries about international shipping. I look forward in hearing from you and thanks in advance!
    Last edited by dhg6; 10-20-2017 at 11:52.

  4. #14
    Join Date
    Jul 2005
    Location
    Tampa Florida
    Posts
    483

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    Sorry I did try to respond. I will take the resistor out of the parts unit and make sure it is the same. I need the temperature sensing diode also, one failed in a head I have and it won't start because the tube is too hot.....when cold. Strange...diode failure? I will let you know....Phil (813) 974-2378 at work.
    Phil Bergeron( AKA 142laser)

  5. #15

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    Sounds great Phil

    Send me a link when you have it on Ebay, with buy it now option and I'll get you paid promptly. Don't worry about posting pictures with the sale as I know what it is and hopefully it will save you a little time. Thank you so much!

  6. #16
    Join Date
    Mar 2015
    Location
    Cambridgeshire, England
    Posts
    333

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    Phil, where's the diode located, maybe there's one in my scrapped head.
    That's a nuisance that the ballast resistor design was changed from my head to the later one; I can only think that they added a voltage sense line into the newer design.

  7. #17

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    Hi Phil, I don't know if you received my last p.m. but it's ok to cut the one red lead and send a piece of HV shrink tubing with it. This will make installing it much easier anyway. Send me a link when it's listed with buy it know and I'll pay for it ASAP! Thanks Phil!

  8. #18

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    Did you ever get this resolved? I have a dead 74 laying around, I could ship the HV bridge to you as a direct replacement. (too bad i didn't see this sooner, I'm never on PL...always on LPF)

    Quote Originally Posted by 142laser View Post
    Sorry I did try to respond. I will take the resistor out of the parts unit and make sure it is the same. I need the temperature sensing diode also, one failed in a head I have and it won't start because the tube is too hot.....when cold. Strange...diode failure? I will let you know....Phil (813) 974-2378 at work.
    Yeah mine had this problem a while back too, it was a pain in my ass. it was reading 0.48V cold, so it thought the tube was hot when it wasn't. Thankfully I had a spare one sitting around from the aforementioned head. it senses the temperature via the diode by the anode, and sometimes the electricity will attack the diode through the glass and ruin it. It had happened several times to mine, and one time i was unlucky and it somehow managed to damage it. I had to carefully pull the tube, replace diode and the thermal compound under the diode and re-wrap it in kapton tape, all while still insulating the leads on the diode to get it to stop happening. it was quite a chore to do. the tipping point is >0.5V for the temp lockout mine reads ~0.62 fully cold according to my LC-500.

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