Running 3 phase 780s on single phase power

[Rich Alderson]

> From: Gordon JC Pearce MM3YEQ
> Sent: Wednesday, January 21, 2009 11:43 AM

> 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.

For a living computer museum, certain tradeoffs *must* be made.  Do you
continue to spin 30 year old disk drives constantly, or do you build an
emulator that looks to the CPU's I/O channels like the original disk?
Do you upgrade power supplies with new aluminum electrolytic capacitors,
or replace them altogether?  If you replace them, do you do so in a way
that is completely reversible, to maintain historicity?

It is intended for the systems in this collection to run, but not to
destroy their historical value in doing so.  So we have alternate wiring
harnesses in KL-10s, we have new caps in PDP-8s and PDP-11s, we have a
Massbus disk emulator that talks to RH20s and RH11s and soon to RH780s,
and we'll continue to develop ways to keep things running as we maintain
their history.


Rich Alderson
Server Engineer, PDPplanet Project
Vulcan, Inc.
505 5th Avenue S, Suite 900
Seattle, WA 98104

mailto:RichA at vulcan.com
(206) 342-2239
(206) 465-2916 cell