Weird Prices on E-Bay

As am I. I'd actually quite liek a 7550 (there's a 68000 processor in them IIRC), but I am not paying $2000 + shipping for one :-) I even have an HP7470 opt 003 -- the HPIL pone, and the HP41 ROM module to drive it. No it's not up for grabs! The HP9125 plotter is fun too. It conencts to the HP9100 expansion conenctor, it grabes the data from the X and Y regiaters and uses that s the cooridiantes. Inside it's not as complciated as you might think, given it's all discrete transistors. There are 4 boards of logic to interface to the strange 9100 signals (mostly flip-flops and diode gates), 2 DAC boards (3-and-a-bit decades, these things habve over 90 transistos on them), and then essentially an analogue XY plotter conencted to the outputs of the DACs. The do exist in the UK. I haev 2 of them (again, I am keeping them). One is a Houston Instruments, the other a Bryans. Both are (mostly) valved. Making one would be quite a fun project if you have a reasoanble mechancial workshop, actually. The Houston doesn't have any really odd bits. The slidewires are actually multi-turn pots coupled to the drive cables for the 2 axes, which might simplify things. -tony