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early 70s V4

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  • #1

    early 70s V4

    Ive got an Ampeg V4 here . 7027 s , non mater vol , with reverb , has the weird 6K11 , . Early 70s ??

    Its all original except for the power tubes and V1/V2 12ax7s . The rest of the tubes are OLLLD .



    Anyway , so you guys that are familiar with these amps -- when do they normally start to break up / overdrive as far as volume level?? I heard they were pretty clean?

    I am running a guitar thru it and the amp is very clean from 1-3 on either volume. But 4 and up it starts to overdrive. The customer doesnt like that and wants a cleaner tone . He plays bass through it .

    So is that normal with these? If not Ill start by replacing old tubes
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  • #2
    The switch above the volume makes a huge difference for breakup. If you are on the 0db setting, that sounds about normal. Set to -9db for cleanest operation.
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


    ​
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    • #3
      I've refurbed several of those. If caps haven't been checked or replaced, I'd start there. I don't recall ever refurbishing one that didn't need caps. And yes, that amp should get quite loud before breaking up. Tubes were usually still good in the ones I refurbed, but that's not to say you couldn't have a tube problem.
      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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      • #4
        Originally posted by g1 View Post
        The switch above the volume makes a huge difference for breakup. If you are on the 0db setting, that sounds about normal. Set to -9db for cleanest operation.
        i think it was on -6 , ill try -9

        EDIT = -9 was the same

        i will try tubes / filter caps

        i found no leaky coupling caps
        Last edited by Valvehead; 02-04-2022, 01:49 AM.

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        • #5
          Also check screen resistors. I've had these amps with only one or two tubes conducting because of open screen resistors.
          "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22
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          • #6
            Originally posted by The Dude View Post
            Also check screen resistors. I've had these amps with only one or two tubes conducting because of open screen resistors.
            And some of them have low value plate resistors acting as fuses.

            Valve Head , when it does break up at '3', is it real loud?
            Originally posted by Enzo
            I have a sign in my shop that says, "Never think up reasons not to check something."


            ​
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            • #7
              Originally posted by g1 View Post

              And some of them have low value plate resistors acting as fuses.

              Valve Head , when it does break up at '3', is it real loud?
              i think so--shakes the house......who knows what the owner considers loud

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