The later SB had a half power jack, that you could plug the speaker cord into. I'm not sure when they started having this feature, but I think it was at the same time that they changed from seperate Fat and Bright inputs, to a single input with a Fat/Bright switch. The tolex is also smoother on the later models, less pebbley. The later ones, also did not have the infamous PCB coating problems, though I think a lot of the earlier serial numbers were repaired under warranty, so they do not have the coating on the PCB.
Who here DOESN'T use the "Classic V" grapic EQ set