I have a tube ID question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by teleman1, Jan 28, 2008.

  1. teleman1

    teleman1 Member

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    WE all see tubes that are 12ax7 size or El84 size with numbers that are wiped off. Is there any way to ID tubes without the labels. For intance;differences from a 12ax7 to a 12at7. aAre there ID's inside the tube or physical characteristics that define each?
     
  2. Groovey Records

    Groovey Records Member

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    Some NOS tube retailers post photos and have details about different markings other then trademark or manufacturer labels.

    Here is one. I have never done business with them just came across the site during my research. I've gotten good stuff from TGP's Mike K.

    https://www.tubeworld.com/12ax7.htm

    Good Luck
    Groovey Records

    Listening to Herbie Mann- Memphis Underground
    on Vinyl of course
     
  3. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    With an experienced eye, one can spot clues from the internal structure, and often make a positive tube i.d. If you have some tubes you'd like to i.d., post clear photos here, and we may be able to help.

    - Thom
     
  4. teleman1

    teleman1 Member

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    Timberwolf or anyone else.

    What does a D on the bottom of a 12ax7 mean. And also,what does a T mean??? The pins surround this number as you look at the bottom.
     
  5. Blue Strat

    Blue Strat Member

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    Nothing on the outside of the glass means anything. Everything on the inside of the glass means something.

    You can't ID a tube without seeing the guts. ;)
     
  6. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Dunno
    Try someone else... like Jeff West - he's the most likely TGP member I know who might be able to answer this question.

    I have been aware that markings in the glass base, between the pins, can help identify kindred batches of some tubes. In my case, it was certain runs of early-'50s Sylvania 12AX7 and 12AU7. But I don't know what those coded symbols actually mean.

    - Thom
     

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