The 500W Gallien-Krueger MB Fusion tube preamp incorporates the same all-tube preamp of the GK Fusion 550 and maintains the amazing portability of the MB2-500. The ultra-light bass amp delivers 500W at 4 ohms, 350W at 8 ohms, and is equipped with an all-tube, 3x12AX7 preamp. The GK MB Fusion bass head also has a 4-band active EQ, variable contour with mid frequency select, and Deep and Bright switches, so you've got total tonal control.