[ Walt Cates, WD0GOF, is probably THE authority on these awesome transceivers. I was fortunate enough to have him go through my SR-150 a few years back. ]
More SR-150 rigs were produced than any other SR series rigs. There were 7 production runs from 1960 – 1965. Documentation on production run 4 authorizes the purchase of parts and build of 250 units.