> -----Original Message-----
> From: IBM Mainframe Discussion List On Behalf Of John Eells
>
> Tom Marchant wrote:
> > On Wed, 9 Jan 2008 09:36:22 -0000, Phil Payne wrote:
> >
> >> ... every machine was powered via motor-generators.
> >
> > For those of you who might not know what that was or why, the
> > processors of that time generally specified 415 Hz three
> phase power to operate them.
> <snip>
>
> True at the high end only. e.g., 168s used MGs because they
> used 415Hz
> power but 158s did not; they just used regular old 3-phase
> 60Hz 220V power.
>
> I never did know why, though. I always wondered whether it
> was to keep
> the number and size of power supply capacitors to a
> reasonable minimum.
Yes, according to my EE colleague.
-jc-
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