3phase power for VAXen [was Re: VAX 780 on eBay]

Rich Alderson cc at alderson.users.panix.com
Tue Jan 4 16:17:08 CST 2022

> Date: Sat, 1 Jan 2022 13:19:51 -0800
> From: Guy Sotomayor via cctalk <cctalk at classiccmp.org>

> On 1/1/22 10:40 AM, Paul Koning via cctalk wrote:

>>> On Jan 1, 2022, at 1:12 PM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:

>>> This:

>>>     https://www.ebay.com/itm/275084268137

>>> The starting price is expensive, but probably not utterly unreasonable,
>>> given that:

>>> - the 780 was the first VAX, and thus historically important

>>> - 780's are incredibly rare; this is the first one I recall seeing for sale
>>>   in the classic computer era (versus several -11/70's, /40s, etc)

>>> - this one appears to be reasonably complete; no idea if all the key CPU
>>>   boards are included, but it's things like the backplane, etc (all of which
>>>   seem to be there) which would be completely impossible to find now - if any
>>>   boards _are_ missing, there's at least the _hope_ that they can be located
>>>   (780 boards seem to come by every so often on eBait), since people seem to
>>>   keep boards, not realizing that without the other bits they are useless

>> Interesting, but the argument for why it's not tested is implausible which
>> makes me very suspicious.  I suppose there might be a few American homes
>> that have only 110 volt power, but I'm hard pressed to think of any I have
>> ever seen, and that includes really old houses.

> Without replacing the power controller in the 11/780, you need 208v 3-phase
> to run it.  It's not impossible...nothing in the CPU actually *needs* 3-phase
> as the individual power supplies are 120v but the overall maximum load is
> greater than a 30A 120v circuit.

> TTFN - Guy

I've been reading this thread for the last few days, without the time to reply.
All the statutes of limitations have run out, so I can tell the story; it will
be clear shortly why I'm piggybacking on Guy's post.

Back in the mists of time, Paul Allen wanted me to acquire a VAX-11/780 for his
collection.  Shortly after that request landed in my inbox, the DECUS DFWLUG
announced that they would not be opening their VAX museum due to the untimely
passing of the gentleman who was driving the effort, and that they would be
disposing of the collection.  I contacted the person who was handling the
deaccession, but he would not discuss it with me because someone else had
already arranged to take the whole collection.

That person was Guy Sotomayor.

Guy sold Paul two 11/785 systems (one an upgrade, with the 780-5 replacement
label!) in chassis, with a third full set of boards as spares.  I flew down to
the Bay Area and had lunch with Guy, saw his DEC-10 and all that, and arranged
for the shipping.

Shortly after that, Paul floated the idea of turning the collection into an
actual museum.  (At the time, the project consisted of me and an electrical
engineer named Keith Perez, who devoted his spare time to helping me keep
Paul's big iron running.  Keith was building the digital control system for
Paul's submarine at the time.)  The project, an online "museum" called
PDPplanet, changed its name to Living Computer Museum; we hired a third
engineer to help, Ian King, who was eminently qualified to get the VAXen up and
running based on his own private collection of VAXen and -11s in his basement.

We did not have a 3phase outlet on the second floor of the building where the
collection was housed, and there was no room for the first VAX in the small
computer room on the third floor, so Ian and Keith came up with an alternative:
They tested all the outlets on the second floor and determined that there were
three within reach of the room in which Ian was going to work on the 785 which
were fed from 3 different phases off the big honking breaker panel (200A
service, IIRC).  Keith put together a box with the appropriate NEMA socket and
three heavy duty cords feeding into it, which in turn were plugged into three
outlets on the walls around what eventually became the vintage exhibition hall
at Living Computers: Museum + Labs (the eventual name of the place after the
modern exhibit space on the first floor was built).

So it's possible to power a 780 or 785 without a power supply rebuild if you
simply have the right (industrial) breaker panel in your building...

Happy New Year, everybody!


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