Control Data 841 disk drive's 3-phase power supply resurrection

[P Gebhardt]

>The claim about the "only CDC disk drive with hydraulic positioner"  is
>false.  Starting with the Bryant 6603, I believe that the 808 and very
>rare 821 also used hydraulics.  Voice-coil positioners started to be
>used with the 844 drives.  I don't recall what the 854 used, as it
>wasn't very common on big CDC iron.
>
>--Chuck
Chuck, thanks a lot for your reply and for these insights! I indeed wasn't aware that within CDC, the 808 and 821 worked-with hydraulics, too. I will update the description on the web accordingly!The 85x drives don't use a hydraulic positioner. To my understanding, they used a solenoid and a carriage assembly that is controlled by a photo-cell, -transistor and a timing wheel with slots. 
All the best,Pierre