My mill is not a bridgeport. But an Enco chinese 2 hp 3 phase. I have an Allen-Bradley converter. Mill is manual speed change. Converter changes it to single phase without any hp loss and gives me variable speed. Plus spindle direction change at the push of a button. I don't know the cost of unit it was given to me as a retirement gift about 15 years ago. It has worked flawlessly. All the info I have is: Bulletin 160 SSC tm variable speed controller (series B) .037-2.2 kw (0.5-3hp)
Hope you all can find the unit. Works great!!