It's a 3.5" drive, and I think it's about 10 years old, but I only have the skeleton (one part of the mounting chassis + spindle motor) to work on right now.

I think I'll rig up a variable regulator. Shouldn't be too hard.... I'll grab a 7805 and figure something out.

Any clues on the encoder output? Could it be a hall effect sensor or something? I have no idea what sort of sensor would be used in this type of DC servo motor. It's not THAT important that I get the feedback working, it's more so I can work out which terminal is which. I guess if I plug it into my PC scope and spin the spindle, two of the terminals should show a (relatively) constant voltage, which will hopefully be the two motor drive terminals.

Thanks for the info, Melanie.