Even with the footswitch off, my Mk III blue stripe is “bleeding” reverb. If I turn the reverb down to zero, it goes away. Would this be a tube issue? If not, where would I start?
I think your amp may be functioning normally. Read the manual for the MkIII. The footswitch does not turn the reverb on/off. The reverb on a MkIII has two level settings so think of the footswitch as a reverb boost pedal. It's only 'off' when the level control is at zero. Some of the other members of the board may chime in and give a better explanation or some technical insight.
