brownface Concert Amp problem - thoughts?

Discussion in 'Amps and Cabs' started by ryandfl, Feb 27, 2015.

  1. ryandfl

    ryandfl Supporting Member

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    I have a 63 Fender Concert Amp. I'm not sure when this problem started, but the vibrato channel is now producing a lot less volume than it used to. I have to put it at maybe 7 to equal what the normal channel is doing at 2.5.

    It is also overdriving in an nasty way when pushed with too much input volume. There is a shrill, alsomost digital sounding edge.

    Any idea what the issue could be? Sound like a bad tube or is this a caps sort of issue?
     
  2. swiveltung

    swiveltung Member

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    Try switching V1 and V2 pre tubes first. if no change,
    Then try different V3 and V4
     
  3. ryandfl

    ryandfl Supporting Member

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    I swapped the preamp tubes for that channel. It actually helped with the tone, smoothing it out and reducing the grating driven sound.

    But the volume gap between the regular channel and the vibrato channel is still there.
     
  4. slider313

    slider313 Silver Supporting Member

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    Time for a trip to the tech. There's probably a bad ground or open resistor in that channel.
     
  5. kbgear

    kbgear Member

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    If that's still a 6G12A in '63, V5 will also be critical for the Vibrato channel if you didn't try swapping it yet. V3 and V4 only drive the oscillator, and aren't in the direct signal path.

    Does the Vibrato channel still... vibrate? ;) Might check with the footswitch plugged in and the Vibrato circuit off/grounded. I'm not sure how, but the Vibrato could be in a "cocked" state, à la a cocked wah... grasping at straws there. Otherwise could be cathode resistors, preamp bypass or coupling caps, etc., as slider mentioned.
     

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