Is there much difference in electronics between the Bassman head and the old Bassman 4x10 combo? I have a blackface head, with 2 channels, 4 preamp tubes, and a pair of 6L6's (but I didn't see a rectifier tube :-(, with a number "67" in one corner of the back panel. It says "division of Columbia Records", so I'd guess the "67" might be the year of manufacture. -- mike