Third generation and lower-end versions of the Biotracer tonearm - but far more reliable than the original PS-B80 :)
The PS-X600 sold like hotcakes, really : there are tens of thousands worldwide.
Above in the lineup was the tangential, excellent and well reviewed in Japan PS-X800 and the rare PS-X700.
Fourth gen' would be the PS-X555ES and... there would be no fifth generation.
Simple, reliable and surprisingly musical - don't hesitate to put a good MC cartridge on your PS-X600, like the Denon DL-160 !
The 200g lighter PS-X500 is the same, sans automatic disc-size selector or side repeat switch.