Here is what the owners manual says:
Your BLUE TUBE is intended primarily for bass, keyboard and guitar players who desire to “warm-up” and enhance their sound by using the classic vacuum tube as the vehicle.
The heart of the BLUE TUBE is the classic 12AX7A twin triode vacuum tube. It is possible to obtain many classic “old amp” sounds with your present solid-state and probably over-processed equipment. If you are using tube equipment, the BLUE TUBE will add even more to the good sound you already have!
I used it primarily to "warm-up" my sound as described, but it will work as an over-drive as well. http://www.genzbenz.com/img/manuals/...UserManual.pdf