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!
> 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
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Received on Mon Apr 19 1999 - 09:45:59 BST