GW-DEC-1: A New DEC Prototyping Board

systems_glitch systems.glitch at
Fri Aug 16 21:33:35 CDT 2019

As Jon said, from my analysis of busted-apart DEC connectors, there's a
selectively plated "pad" where the contact surface actually is.

I wouldn't be surprised if the bulk of the contact fingers is *phosphor
bronze* which is often used in springs. Perhaps we can get Connor to do a
metallurgical analysis once he gets the EDX attachment for his SEM going!


On Fri, Aug 16, 2019 at 10:21 PM Jon Elson via cctalk <cctalk at>

> On 08/16/2019 05:59 PM, Noel Chiappa via cctalk wrote:
> >      > From: Brent Hilpert
> >
> >      > I've seen pieces of HP high-end lab equipment from thru the 60s
> that
> >      > used tin plating on the PCB edge fingers, mating into gold-plated
> edge
> >      > connectors on the backplane.
> >
> > ISTR that DEC used bronze contacts in their backplanes, but basically
> all the
> > boards had gold-plated fingers. (I think I've seen a few power supply
> boards
> > that had tinned fingers.)
> >
> > I think the bronze was preferred since the contacts bend back and forth
> as
> > cards are inserted/removed, and bronze is more durable; and being part
> tin,
> > has the same corrosion characteristics are the tin.
> >
> >       Noel
> >
> The contacts were mostly phosphor bronze, but they had a
> little spot of selectively plated gold where the PC board
> finger actually wiped.  I think they used basically the same
> technology from the PDP-8 era to the VAX 7xx series.
> Jon
> Jon

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