On June 10, 2014, Kevin Hayes was issued U.S. Patent 8,749,310 for "amplifier bias control". This patent covers the only known technique for observing the true underlying quiescent current (idle current) of an output tube (or transistor) under dynamic signal conditions, and then holding it to the stable target value with a precision of 99% or better. It is the only 'auto bias' system in which the volume and character of the music being played does not alter the idle point of the tube. It is incorporated in VAC power amplifiers as the iQ Intelligent Continuous Automatic Bias System. In addition, the iQ system defends against short circuit tubes, prevents gas current run away tubes, indicates weakening tubes, and minimizes noise and distortion. Current iQ models are the VAC Statement 450 iQ and Signature 200 iQ.
