The Seymour Duncan Twin Tube Classic SFX 03 is a high-quality, two-channel, guitar preamp that uses a duet of premium, mil-spec, subminiature 6021 vacuum tubes. The 100% vacuum tube signal path with a high voltage power supply allow the tubes to operate at their fullest potential and provide maximum dynamic range, the most gain, and the smoothest tone. The result is the classic tube sound, smooth distortion, and low order harmonics you expect from a great tube preamp.