seymour duncan 84-40 no tone controls

[ptmo]

I just picked up a duncan 84-40 tube amp and none of the tone controls do anything .the amp still has plenty of volume and both channels work (shared EQ) but adjusting any tone control even the bright switch has no effect .anything I can check before I take it to a shop ,or suggestions on what I can expect them to tell me..

[stokes]

Check that the ground connection from the outer lug of the mid control is connected to ground.Some people lift this ground to bypass the tone stack and effectively boost the gain of an amp.