Johnson Millennium

Mark uses the Millennium combo as a practice amp backstage before shows.  It is said to be one of the best modeling amps ever made, and with its tube-integrated preamp, does a fantastic job of reproducing the sounds of many popular amps including the Mesa/Boogie Dual Rectifier and Mark II, the Marshall JCM800, and the Matchless DC30.

Johnson web site
Harmony-central listing