How scarce (valuable) is core for the PDP-8?

From: Lawrence LeMay <lemay_at_cs.umn.edu>
Date: Mon Apr 19 10:21:09 1999

> When I mentioned the chance to buy a 4kW stack for the PDP-8/i for $100...
>
> --- Lawrence LeMay <lemay_at_cs.umn.edu> responded:
>
> > Actually, that's probably a reasonable price.
>
> Foo!

Well, I didnt say that I would pay $100... Or that it was a great price.
But it might be a fair price.

Of course, If i didnt already have a bunch of core of various types, and
if i needed it to restore a pdp8 system (which would be at the
absolute top of my list to do, as the first computer I ever saw, and
every used, was a PDP8/e) then I would probably pay it. And i'd be
cursing at whatever the past 20-30 years had done to make the board
not work anymore ;( And i'd probably try to locate Lassiter and see
if my some miracle he could repair the board, etc.

But, thats just me. To me, having a PDP8/e is the ultimate dream machine.
That, and having the room to store a PDP8/e...

-Lawrence LeMay

>
> > Core memory boards, probably non-working, have been going for a high price.
>
> I got sniped for a PDP-11 double-core stack this weekend, backplane included,
> that went for $38, no reserve.
>
> > Age and a nice visible setup increase the price.
>
> The core stack for a PDP-8(i|L) is older than much of what's on the
> market, but none of the good stuff is visible at all on it.
>
> > Now, I havent seen the memory in question. but the pdp8/e core
> > memory i've seen is all covered by a clear plastic shield. This
> > increases its value as a display piece, as you can easily see
> > all the core, and its all protected.
>
> It's hard to describe the arrangement, but the core plane in question
> here is a block with two edge-connectors on either side, "dual-height"
> as they say, but it's much thicker - let's try bad ASCII art to illustrate...
>
>
> ######## ########
> xxxxxxxxxxxxxxxxxx == ######## ########
> ######## ######## ######## ########
>
> core planes paddle-boards with wire harness
>
> The outside of the core plane part is covered in a "diode matrix", with
> a wad of twisted-pair wires that go off to paddle-boards, one for the
> sense bits, one for the inhibit bits. The address lines come up the diode
> boards, the data comes up and down the paddle-boards.
>
> There are several PCBs with core in the core stack, 4-bits per layer with
> an optional parity layer that has one pad of bits and three pads of core-less
> X-Y wires. None of this is visible when the plane is assembled, and it's
> soldered together with lines of wires going up and down the planes.
>
> > Of course, in order to use the core on a pdp8/? you would need
> > a couple of support boards in addition to the core plane board
> > itself. I would say that just the core plane, being of a nice
> > size, and being very good 'visually' to display, and somewhat
> > because its a PDP8 series board (nostalgia value), that its
> > probably worth $100 all by itself. If it comes with the 2 support
> > boards and the top connector things at that price, then i'd say
> > its a bargain.
>
> You are thinking of newer hardware. The pre-OMNIBUS 8's have a wad of
> individual, single-height cards that contain the sense-amps and the inhibit
> drivers. I have a pile of them from an -8/L that someone else had already
> begun to strip for parts before I bought it (it also happens to contain the
> only DEC lock that does *not* use the XX2247 key). I'm not worried about
> the analog stuff... I need the core.
>
> Of course, as Allison pointed out, I could always stick in a lump of battery-
> backed static RAM. I was contemplating building a wiring harness to adapt
> an RX8E on the back of either an -8/L (which has 8kW of core out of 12kW in
> an expansion cabinet) or on the -8/i. I would use berg connector pins to
> stick the wires on the back side of the backplane (to avoid soldering, of
> course; but worst case, I just wire-wrap on a connector or two and use
> sheilded ribbon to move the signals around.
>
> The joys of restoration in a market of scarcity. :-P
>
> -ethan
>
Received on Mon Apr 19 1999 - 10:21:09 BST

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