VAX 780 on eBay

Jon Elson elson at
Sat Jan 1 14:32:59 CST 2022

On 1/1/22 1:56 PM, W2HX via cctalk wrote:
> The other benefit to 3phase power to something like a computer is that the filter caps required can be much smaller. Once you rectify three phases 60* you get MUCH less ripple because every 60 degrees you have a new peak arriving. When you have a real gas (electron) guzzler like one of these, DC filtering becomes an issue.
But, they DIDN'T!  All power supplies on the /780 were 
single phase.

On the IBM 370/145, they used a motor/generator set to 
convert 208/3 phase 60 Hz power to 415 Hz 3-phase 120 V 
regulated power, then fed that to 3-phase 
transformer/rectifiers, and finally to low-drop regulators.  
They also used "electronic capacitors", which was a scheme 
to pull extra current through the smoothing inductor during 
the voltage peaks, to even out the ripple.  The 370/145 had 
2 power supplies, one for +1.25 V 390A and the other for -3 
V 390A.


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