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Thread: B-52 AT-100 reverb problem

  1. #1
    Junior Member
    Join Date
    Mar 2007

    B-52 AT-100 reverb problem

    Hi all,
    I'm new to tube amps and I have a problem with my reverb not working. The light on the footswitch lights up, as well as on the head, but no reverb. It uses a 12AT7 for the reverb. The next message is a diagram of what I have. The 12AT7 seems out of place to me and it is one of the tubes that glow on standby. Are my tubes mixed up? Also, does anyone know the tube assignment on this head? I mean, what tubes are for what? The diagram is just the pre-amp section.

    Thanks for any help!


  2. #2
    Junior Member
    Join Date
    Mar 2007
    11 22 33 44 55 66 77
    11 22 33 44 55 66 77
    11 22 33 44 55 66 77

    Tubes 1-3 = 12AX7EH (1 & 2 have metal covers over them)
    Tube 4 = 12AX7B
    Tube 5 = 12AT7 (Tubes 4-7 glow when on or in standby)
    Tube 6-7 = 12AX7B

    I have no clue what tubes are for what. I should have:

    pre-amp - 4 12AX7
    phase inverter - 1 12AX7
    reverb - 1 12AT7
    effects loop - 1 12AX7

  3. #3
    Junior Member
    Join Date
    Dec 2007
    Highland, MI

    B-52 AT-100 reverb problem

    The complement for the AT-100 according to B52's website is this:
    AT-100 Tube Chart
    Power: 4 6L6 / 5881
    Preamp: 4 12AX7
    Phase-Inverter: 1 12AX7
    Reverb: 1 12AX7
    Effects-Loop: 1 12AX7
    Rectifier: 1 5AR4

    However the unit currently in our shop has a 12AT7 in the 5th position. The 12AT7 is a medium gain tube and does have the same pin-out as the 12AX7 high gain tube. Usually the two tubes can be interchanged without extremely adverse affects (things burning up, it may distort), however i am not suggesting this course of action. I would suggest you try another reverb tank, any will do for testing (might not sound right, but you'll know if the tank is bad). Looks like this post is a bit dated, but i figured id reply anyway.

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