Unable To Remove Cover For 12ax7 Preamp Tube On Jcm 900

Discussion in 'The Workbench' started by 19rellimcm37, Aug 13, 2018.

  1. 19rellimcm37

    19rellimcm37 New Member

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    Hello, first post here.

    I am trying to re-tube a Marshall JCM 900 Head with new tubes. I've run into a snag and don't know if anyone else has had this issue.

    I'm unable to remove the tube cover on one of the preamp tubes. For the other two, I just push down and turn counter-clockwise and it comes off. The one that I'm having issue with. I can turn it, when pushing down, however it won't come off.

    I worked at it and still can't get it.

    Was wondering if anyone else has had this issue and how they fixed it.

    thanks
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Welcome to the forum.

    [​IMG]

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    Last edited: Aug 13, 2018
    Mitchell Pearrow likes this.
  3. Micky

    Micky Well-Known Member VIP Member

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    Try some De-Oxit. The kind with lubricant.
     
  4. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Just look at it and make sure the nibs on the base are lined up with the grooves on the cover. Sometimes they seem like they won’t come off. Just pull. It’s thin aluminum.
     
  5. 19rellimcm37

    19rellimcm37 New Member

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    I don't have De-Oxit, however I do have a can of CRC QD Contact Cleaner, can I use that?

    Also where do I want to spray, if I can use this?

    I'm not sure what you mean by the nibs, are the the small round parts sticking out of the cap? I think I have them lined up, and I try to pull, however nothing...
     
  6. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

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    He He just a wee bit of overkill, don’t you think Ampmad
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    If it rotates it should pull off. Yes, those are the nibs.
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    [​IMG]
     
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  9. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

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  10. Kutt

    Kutt Well-Known Member Gold Supporting Member

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    Is it this style tube shield? If so, try to see if the "nub" / retainer I circled below is getting caught on something.

    upload_2018-8-15_10-37-19.png
     
  11. mickeydg5

    mickeydg5 Well-Known Member

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    If it is stuck because of rust/oxidation then loosen it up with one of these.


    upload_2018-8-15_20-44-50.jpeg
     
  12. 19rellimcm37

    19rellimcm37 New Member

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    I got it. I gave it a light spray of that contact cleaner and that seemed to do the job as it came off. I was going to post pics, but they are too big!

    thanks
     
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