Just picked up a B18N head lastnight and I'm trying to date it. The serial number is 039283. The head sounds amazing. The 7027A tubes are Sylvania. The 6SL7 tubes have an Ampeg stamp at the base of the tube. The 5AR4 just says it was made in Britain. The 7199 is an RCA. I think most of these are original. The only thing I'm going to have to get is a replacement for the non-stock bass knob. An amp tech gave it a clean bill of health. I'll post pictures when I finish my move to Washington.