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Vox AC 30 Voltage and popping problem.

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  • Vox AC 30 Voltage and popping problem.

    Hi guys,

    Are these voltages normal for VOX AC30? I rebuilt this amp with new board and parts to original ac 30 chassis.

    32V DC at PI grids when working, -550mV at 2 of EL84's grids when standy by.

    In addition to these, amp is popping when i hit the cabinet. And also harshness sound at high volumes (vibrating cabinet).

    Could you help me please? Could you show me the way? I can post photo or video, make voltage or scope readings as you want.

    Thanks. Okan

    Click image for larger version

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  • #2
    So you have -550mv only on V5 and V7? not on the V4 and V6?
    What kind of voltage are you looking at on all four EL84 grids when out of standby mode?
    Maybe you should look at this:
    http://www.ampbooks.com/home/classic...c30-power-amp/
    Last edited by gearhead63; 06-23-2014, 05:27 PM.
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    • #3
      Please post the complete schematic of your build, including the standby arrangement.
      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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      • #4
        Originally posted by Rockstar Okan View Post
        32V DC at PI grids when working
        You often get silly readings when measuring the PI grids. Try measuring the the common PI cathode connection. I measure 60V there which is similar to the voltage marked on the AC30 schematic.

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