Plessy core memory

Chris Zach cz at
Sun Jan 9 20:06:21 CST 2022

> If you have a 10-1/2" box, you can mount a MUD backplane - but you might
> still have an issue because the older BA11-D boxes use the old 9-pin power
> connectors, and the MUD backplanes (DD11-C, -D, etc) all use the newer 15-pin
> ones.

There we go. I have an 11/05 in a BA11-D box with a DD11-B expansion 
backplane with a 9 pin power plug sourcing +15, -15, +5.

So is the DD11-B a MUD backplane? If not, what is it?

> The later /05's, /40's and /45's were the first ones to provide +20V, for the
> then-new MM11-U. On machines which took H744 'brick's, the _later_ harnesses
> could take a H754 +20V, -5V regulator 'brick'. Alternatively, _some_ BA11-L's
> (used for the /04 and /34) had the right version of H777:

Hm. So I could get the power for the +20/-5 by replacing the 744 with a 
754 and wiring up my own harness. However that would have two problems:

1) I'd be low on +5 for things like an RL11 controller.
2) I don't know if the DD11-B uses the 20 volt and -5 volt lines for 
something else.

This is so much fun!


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