Just had this done to my SF bassman, and it is wonderful. It converts channel 1 (Bass) into a plexi/tweed type circuit, and channel 2 (Normal) to AA164 blackface specs. The reworked Bass channel is simply unreal, the best tone this amp has ever produced. This amp was on it's last leg, and David brought it back and onto another plateau of good tone. Not to mention he was very easy to work with. I highly reccomend his work, and if you have a stock SF bassman, by all means send it his way for a new lease on life.