Jeff, I can't tell from the SN (cause I'm no expert on that), but you can open up the head and look for dated inspection stamps. The Coliseum opens up fairly easy and it would give you a good chance to get all the dust and cobbwebs out of it. I have a solid state Sunn Coliseum Bass head that dated '73 by checking the inspection and acceptance stamps, and a SUNN Concert head from '71. I'm still trying to date my minty Sonic 1'40. I just haven't had the desire to tear it apart yet while it functions so well and is still clean.
If anyone knows where I can get a compatible switch for the Concert Bass head to switch from clear to distortion and back again, please let me know.
