1959HW at full blast when volume is on 1

Discussion in 'The Workbench' started by bigbadorange, Jan 14, 2020.

  1. bigbadorange

    bigbadorange Active Member

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    Picked up a 1959hw a few months back and everything was fine. But now it seems cranked when the volume is on one. This happens when plugged into either of the two inputs with the matching volume, and when jumped. I know this amp has a lot of power, but 1 is just blasting and when I connect my hotplate attenuator, it is lighting up the room when the amp is on one. (lights roughly indicate how much power is coming out of amp). I will probably take it to a tech (Im lucky to have a marshall certified service center not far from my house), but I am capable of doing doing basic trouble shooting on a tube amp.

    Any suggestions as to what to look at that would cause this?
     
  2. neikeel

    neikeel Well-Known Member

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    If everything else is as it should be (EQ controls and presence etc) and the amp is unmodded then it would sound like a faulty volume pot. However you say it does it on both channels?
    If you turn both volumes on 0 unjumpered I presume it is quiet?
    To clarify, if you plug into channel 2 (no jumper) high or low with channel 1 turned off completely you get big jump in volume?
    Similarly if you turn channel 2 off and plug into either channel 1 inputs the same happens?
    Do these things first.
    Then spray some lubricating contact cleaner on the input jacks and insert a jack plug a dozen or times back and forth into each jack and then recheck.
    Applying logic and knowing the simplicity of the premp it is something straightforwards. I doubt that your pcb is conductive or you are arcing within a preamp tube, but the vol pot actions need clarifying.
     
  3. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    A. The ground connection to the pot is broken.
    B. The pot is defect/cracked.etc..
     
    johan.b likes this.
  4. Im247frogs

    Im247frogs Well-Known Member

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    What happens when it's on 10?
     
  5. matttornado

    matttornado Well-Known Member

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    My 1974 super lead is like that too. Sounds the same from 2 -10 on the volume 1. I tried replacing the pot of the same type and still the same thing. The 5000pF cap is removed also. No broken grounds...... My amp is basically On or OFF! lol

    The 2nd channel or normal channel seems to have a little more change as it's turned up though.
     
  6. tschrama

    tschrama Well-Known Member

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    Might be linear pots. Logaritmic repond more gradually. Logaritmic pot have an 'A' a designation; linear a 'B'.
     
  7. matttornado

    matttornado Well-Known Member

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    Nope. I used the same type. (1meg audio) My 1meg audio PEC pot was basically an off /On switch when I tried it.

    The amp been like that ever since I got back in the early 90's.
     

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