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

Chuck Guzis cclist at
Sun Feb 18 12:33:11 CST 2018

On 02/18/2018 09:34 AM, P Gebhardt via cctalk wrote:
> Hello list,
> currently, I am in the process of trying to bring back to life a disk drive installation from Control Data known as "841 Multiple Disk Drive" ( MDD ). From the early '70s. It uses hydraulic disk head actuators! Pictures of the subsystem are here:
> I started with the power supply. Most of the electrolytic capacitors need to be reformed which is being done. 
> As far as I know, some computer installations used 400Hz 3-phase back in the days. Does anybody know, if that is the case for this type of drive systems? I couldn't find any indication so far, except for the input filter that supports up to 400Hz (written on it). 
> I've quite some experience with old linear power supplies, but never worked with three-phase supplies, yet.
> Has anybody experience with this? Anything particular to be considered?
> There is an operator's manual, but there don't seem to be manuals or schematics about this type of CDC drive nor on bitsavers, neither elsewhere on the net. How could help me in pointing out where to get these?
> A lot of questions, I know.... :)

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.


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