I bought my PX-10 in Frankfurt, West Germany just after I arrived there as a guest of Uncle Sam in February, 1972. There were 2 PX-10's available at that time: PX-10A (amateur) or PX-10E (expert). The E model was 531 with upgraded components. I later acquired a PX-10E which I still have-well, the frame, anyway.
Rick Chasteen, Kansas City