IBM 1620

Dave G4UGM dave.g4ugm at
Sun Aug 30 03:49:00 CDT 2015

 -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Tothwolf
> Sent: Sunday, August 30, 2015 1:57 AM
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at>
> Subject: Re: IBM 1620
> On Sat, 29 Aug 2015, Paul Koning wrote:
> > On Aug 29, 2015, at 12:36 AM, Lyle Bickley <lbickley at>
> wrote:
> >
> >> I was not on the Team that did the memory analysis and the ultimate
> >> "modern" replacement memory. However, when I joined the Team, I
> asked
> >> similar questions and was told that the core memory was literally
> >> "falling apart" and was not repairable.
> >
> > I sure have a hard time fathoming any of this.
> >
> > Quite apart from the obvious one of building a pin-compatible modern
> > memory, another answer comes to mind.  If a core plane has come apart,
> > the cores could be recovered and restrung.  That requires patience and
> > dexterity, but it should be doable.  It also requires a device to hold
> > the cores correctly for threading; something like that could easily be
> > made in a a 3d printer.
> Those particular cores are quite small and I'm not sure a 3d printer would
> able to print a jig with the tolerances required. 

Perhaps a consumer 3-D printer wouldn't, but there are higher precision
printers out there that will print to a high accuracy. 
Also not that 3-D printing with filament is just a small part of a wide
range of techniques available. There are several processes:-

some of which are not available to the Amateur because of cost (especially
un-expired patents) or just too complex...

There are also subtractive manufacturing methods such as laser
cutting/etching and CNC milling which could be more suitable for building a
core jig....
.. Most of the FabLabs will have one of these available

and a laser cutter....

>IBM had special machines to
> position and thread them.

Thanks for posting that. Very interesting. Looking at it, the machines are
extremely complex, but I am sure they could be reproduced, albeit at a
probably prohibitive cost...
.. I have marked for later reading...

> I can certainly understand why repair wasn't initially attempted, however
> that doesn't mean it is impossible. Given the rarity of the system,
> new stubs of wire to the original enamel wire or completely rebuilding the
> core planes with all new wire might still well be a worthwhile project at
> point in the future. It might even be possible to keep most of the cores
> position and rethread just one portion (X, Y,
> sense/inhibit) at a time.
> Another plus is that because of the way the wires are threaded, it is
> that any of the cores have been lost, even if a large number of wires have
> broken at the terminals.

Dave Wade

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