TUBE DRIVER Original by BK BUTLER with BIAS CONTROL TUBE DRIVER with BIAS Control -Original Design by BK Butler. Each one is hand made and checked out carefully by BK himself! Here's your chance to own this legendary "Holy Grail" of overdrive pedals. Known the world over for creating the Eric Johnson 'violin tone' and as one of two main pedals used by David Gilmour. Heart of the Tube Driver is a real hand-selected 12AX7 tube by BK Butler himself.. Controls: Tube Drive, HI & LO EQs, Output Level and custom Bias. Compatible with all electric guitars and amplifiers.