Synergy Engl Powerball, Module for Synergy System, All tube, Designed by Horst Langer and Engl Amplification, The blue channel is based on channel 3, the red channel on channel 4 of the Engl Powerball, 2 x 12AX7 tubes, 2 Channels, Separate 3-band EQs, Gain and volume controls, The three-stage cathode selector switch allows you to configure the input tube bias setting for optimal input gain and bass response