From Jeff Makos:
"S.O.B. ("Son of Boogie")"
"The S.O.B. was introduced sometime during the Mark II era. This was Mesa's first attempt at having a "reissue" of the Mark I. It had 2 inputs and its controls were Volume 1, Volume 2, Master, High, Middle, Low, Limit. The "Limit" seems to give distortion to the amp while maintaining the volume. It wasn't really a Mark I, however, and it does not have a great reputation."
[/url]http://home.earthlink.net/~ayan/history.htm
I've read that the limit was a bu... isn't the amp for you. Great price, though.