IBM 1620

Paul Koning paulkoning at
Sun Aug 30 13:15:03 CDT 2015

> On Aug 30, 2015, at 1:55 PM, Chuck Guzis <cclist at> wrote:
> On 08/30/2015 09:47 AM, Tothwolf wrote:
>> If repair of the core memory in CHM's IBM 1620 is ever attempted, I
>> think either low-tin solder alloy with 1-2% added copper or possibly
>> a more modern indium-lead solder alloy would probably be the best
>> choice for the enamel wire to terminal connections since that would
>> greatly reduce the likelihood of any future wire breakage.
> Wouldn't solderless bonding/welding be a better alternative?

That's what the IBM IEEE article mentions.

I'm still a bit puzzled by the dissolving of copper wire by conventional solder.  The wire used in core memories is thin, but not outrageously so by the standards of, say, Litz wire, and that is soldered routinely.

> ...
> So there'd be what, 120,000 cores to thread?  That might be a bit daunting from a human-hour standpoint.  I'll wager that 120K cores wasn't even a day's output for outfits like Fabritek.

Those cores weren't threaded one by one.  You'd start by setting the cores into a holding jig, which positions them correctly.  Then you thread wire from edge to edge.  The article mentions a needle with the wire welded to its end; that makes sense because the copper wire is unlikely to be stiff enough.  So the number of individual threading operations is 3-4x the square root of the core plane size.  For example, on a 4k core plane, it would be 200 steps, give or take.  (A bit more on a CDC 6000 series core plane with its peculiar 5 wire architecture.)


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