Plessy core memory

Nigel Johnson Ham g4ajq1 at
Sun Jan 9 16:48:28 CST 2022

I would assume that your 11/10 has the suffix -NC.  There were two 
versions, the -NC used -15V four wire memory, and the later -SC used 
+20V three-wire memory.

The +20V was provided by a MUD slot (Modified Unibus Device) and there 
was usually a big red sticker in it warning to not plug a module in that 
was not wired for it.

I believe it was standard in all models after the second version of the 
11/05 -/10

I once tried to fix an 11/34 off-contract that somebody had done exactly 
that to- I gave up when I found that the +20V had been routed to some 
unobtainable ROMs on the CPU board.



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On 2022-01-09 17:04, Chris Zach via cctalk wrote:
> I'm working on my pdp11/10 getting it back together. One problem I 
> think I have is that the secondary memory (a Plessy 700101-100) may be 
> shorting the -15 line for some reason. Working on it, but does anyone 
> have a manual or anything like that for this kind of memory board?
> Alternately, what kind of Unibus 16k memory board exists to get a 
> 11/10 from 16kw to 32kw of memory? Apparently I can't use a MM11-B as 
> it requires +20 and -5, both of which are not provided by the power 
> supply or sourced on a DD11-B backplane module. The 11/10 has +15, 
> -15, and +5.
> On a related note, where did +20 come from for Unibus and which 
> systems even supported it? Was it an 11/45,11/70 thing?
> Thoughts?
> C
> (Yes, I could build a regulator to take the 30 volts between +15 and 
> -15 and create an independent 20 volts. Maybe. Likewise I could 
> generate -5 from the -15 and a 7815 regulator. Maybe.)

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