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  • old Alamo amp

    Im playing around with a small combo--an old Alamo amp.

    This has a 35W4 rectifier tube. Im not getting any Dc voltage anywhere in the amp. None of the tubes light up at all.

    The trans is sending 70vac to the 35w4, and thats it.
    tried 2 different rect. tubes so its not that. grounds test good.

    any ideas? anyone familiar with these old things ?

  • #2
    A 35W4 is generally used in heater series strings, hence the odd voltage. Usually paored with a 50C5 and a couple 12v tubes. All in series, that adds up to approx the mains voltage, which would be directly applied.. SOme used a big power resistor to drop some voltage in place of a tube heater.

    At least one Alamo model used a tap off the high voltage secondary of the PT for the series string, instead of directly off the mainis.

    SO if the heaters don;t light, either you don;t have all the tubes installed, or one is burnt out, or ther is a broken connection.


    And with no heater, the 35W4 can't rectify anything to make any DC anywhere.

    http://www.schematicheaven.com/barga...capri_2360.pdf
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      got it ---

      it was a bad 12Au7 tube. amp is working , thanks !

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