Originally with the round dials it was a motor generator, MG, (Ward Leonard) drive, with a very large diameter DC motor. iirc 3.5 hp. Lots you can read about that set up, but it performs! 10 rpm to 2500 with two speed back gear (designed in the lathe '30's!). That is very difficult to replicate. On mine, I had the two speed gearbox box but not the MG. I went with a 5hp AC motor and VFD and made the two speed gearbox the front of the motor. It does well for the practical purposes to which I'll put the lathe (I have another lathe that will go down to 17 rpm via gearing when very slow speed is needed) but it does not equal the original MG drive's performance. The criticism of the MG drive is its noisy.