Running 3 phase 780s on single phase power

[Ian King]

>-----Original Message-----
>From: cctalk-bounces at classiccmp.org [mailto:cctalk-
>bounces at classiccmp.org] On Behalf Of Roy J. Tellason
>Sent: Thursday, January 22, 2009 10:41 AM
>To: General Discussion: On-Topic and Off-Topic Posts
>Subject: Re: Running 3 phase 780s on single phase power
>
>On Wednesday 21 January 2009 02:42:35 pm Gordon JC Pearce MM3YEQ wrote:
>> On Wed, 2009-01-21 at 19:13 +0000, Tony Duell wrote:
>> > > > Umm.  No.  That transformer is a ferro-resonant transformer.  It
>> > > > *needs* 3-phase to work!  It supplies the basic 12v DC that are
>then
>> > > > used to by the linear regulators.  It's those that burn the
>power as
>> > > > heat.  Replacing the linear regulators with switchers will
>reduce the
>> > > > consumed power by a lot.
>> > >
>> > > Since extremely high current switchers are relatively cheap (at
>least
>> > > compared to getting three-phase installed, and massive aircon
>systems),
>> > > is there any reason why you *wouldn't* go down this route?
>> > > Particularly for a machine that's going to be on a lot?
>> >
>> > Err, historical accuracy? The PSU is as much a part of the system
>design
>> > as the CPU (OK, maybe I exagerate, but not by very much). I know
>that if
>> > I owned a large adn rare machine (large VAX, PDP10, etc), I'd want
>to
>> > keep it as original as possile.
>>
>> That's all very well, but if it costs you three times as much to run
>> because of the huge inefficient power supply then it all starts to
>seem
>> less practical.  That's the sort of thing that makes the difference
>> between a viable system that you can actually use and enjoy, and a
>bulky
>> ornament.
>
>I guess that's the difference between wanting something so you can
>_have_ it
>vs. wanting something so you can _use_ it.
>
Or, it's the difference between pragmatism and historical preservation.  We try to preserve the system as closely to its history as possible, while recognizing that sometimes compromises are necessary.  Sometimes, those compromises even reflect history: for instance, the replacement of linear supplies with switching supplies in PDP-10s, which seems to have become common practice as the model line matured.  Our goal is always to have a system someone can _use_, as we work to develop a 'best practice' that addresses that while maintaining the historical integrity of the original machine.  -- Ian