KM11s and the PDP-11/20 (was Re: Help w/DEC H742 +15V...)

Ethan Dicks ethan.dicks at
Tue Apr 14 08:15:59 CDT 2009

On 4/14/09, Henk Gooijen <henk.gooijen at> wrote:
>  Hi Josh and Ethan and all readers :-)

Hi, Henk,

>  I also got the KM11 from Guy, only the bare boards. I still need to
>  assemble them. I did not buy the switches ...

I think I have all the parts on hand except the switches.

>  I have an 11/20 which might require some work, and indeed my 11/20
>  also has "memory problems": none present at all.

Hmm... that's a problem.  ;-)

>  I will not search
>  for quad-sized core memory sets for the 11/20, but use an expander
>  box (plus BC11 cable) and some simple MOS memory modules.

Fair enough.  I have enough parts (and BA-11ME cabinets) to put some
core memory on mine, but unless I happen to find a 4K core stack (or
perhaps _any_ core stack to swap with my former co-worker that has the
one - it's just a wall-hanging to him), I'll probably go for 16kW or

>  When I'll
>  start working on the 11/20, I might have a few questions ...

I'm sure I'll be in the same boat when I get to that point, too.
You'll probably get there first, so I'll be interested to hear what
questions you come up with.

Mine is missing the H720 PSUs (I looked it up last night in the copy
of the PDP-11 handbook on Gordon Bell's webpage), but I think I have
the single-height paddle cards to get the power into the individual
backplanes, or at least some of them.

>  Anyway, are you sure you want M920's Ethan?  Not M9202's?
>  That's almost the same issue as G727A (knocklebusters) vs. G7273's.

Yes.  I really want the short, stubby M920s.  I've already had one
off-list offer for some at a good price and a lead on some others.

The M9202s are great for newer systems where you might be
reconfiguring things often (11/24, 11/34...), but the M920s are period
for the 11/20.

>  But if you really want M920's, I can miss two of those, maybe 3,
>  I'd have to check.  Just let me know!

Why don't you check and let me know off-list what you find.



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