Do some circuits lend themselves to being able to get controllable feedback? That is at similar volume levels would a tweed deluxe more readily feedback than a Deluxe Reverb or a Princeton Reverb? Plexi vs Vox, etc.? How about differences between humbuckers vs single coils vs P90 pickups? I'd like to be able to get controllable feedback at small club volumes and classic rock gain levels like Neil Young Crazy Horse up to say AC/DC at the gainy'est. Another example I love is the feedback during the first 10 seconds of Begin the Begin by R.E.M.