I had a Lionel O(n3, -27?? not sure) It had the 3-rail track, with an AC pwr supply. Sure wish I still had it.. it was a "hand-me-down" from some older cousins. They were 8 yrs older then me, I got it in the 60's so it would have been a 50's era set. A steam loco, tender, box car, gondola...