i have a 1973 concert bass head...the thing is loud that's for sure..it's the silver face head...sunn made that line in the early 70's..don't know what the cut off date was..your model sounds like it's past 1975....the number II might be the way of sunn saying you run that head with two cabs....there might be some other guys that can help you with the date of your amp...there's a well of info on this site...lots of sunn brothers with lots of info and knowlege about the amps and cabs....but.just by reading the post over the last few years i would say alot of the guys have amps backing up from 1975 back on down to 1966...their the hard core guys..me included..it seemed when sunn took off with their first amps , the company found their sweet spot as soon as they started to build and increase their production..their amps, to me was like from 67 to 71...the collectables...the holy grails ...THE AMPS TO OWN. without a doubt. the best tube amps ever built....and, a foot note...any of the model t's was a great amp..it fit into any playing nitch..with guitar of bass....that amp got the job done...but..the amp that your looking to buy...just buy it ...smiles...Bob from mass
