They were limited on the first run. There was a second run that was cancelled. Modifications were made to some of the B-units for more power. Takes a large layout. Is all brass with good detail and paint. I believe there were only 27 units. 18 A units and 9 B units, used for commuter service, Long Island, NY. Run as A-B-A consists. Had significant problems and would not MU with anything else. Forum member, Neil Schorr, spent a lot of time on this project for Joe Hayter/Weaver models at the time. Interesting to note that there were probably more O-scale models than 1 to 1 units. One of my favorites. May be a must for a Pennsy modeler???