BC11A paddle boards

Guy Sotomayor ggs at shiresoft.com
Tue Jan 26 17:17:01 CST 2016

> On Jan 26, 2016, at 3:03 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
> On Tue, Jan 26, 2016 at 5:46 PM, Guy Sotomayor <ggs at shiresoft.com> wrote:
>> I just received the first of the BC11A paddle boards (so that I can now create my own BC11A cables).
> Cool!
>> For those who’d like to know, I probably will not be making a production run of these boards unless I get a *lot* of interest (100 boards or so).  If you want some, let me know and if I get enough interest, I’ll do a production run.
> Considering DEC did something like this for the DWBUA, but with 4
> 30-pin cables (by necessity because of the BI backplane), is 2x60 pins
> more cost-effective than 4x30?  Mostly, I'm curious about how much
> 60-pin ends cost and the difference in cost between 2 lengths of
> 60-pin ribbon cable vs 4 lengths of 30-pin cable.  The copper cost is
> the same, but I wasn't sure what the current cost-per-foot is for
> ribbon cable.  I haven't bought a reel of it in 30 years, but I do
> recall that 40 pin seemed to be more expensive than 4 times the length
> of 10-pin, for example (since we used both where I worked in the 80s).
> Either way, these days, the cost of 2x60 vs 4x30 is probably minor
> compared to the fab costs of a "large" PCB with gold fingers.  I'd be
> curious to know how much a 10' BC11A-work-a-like will run, but I'm
> vaguely interested in some pairs of boards.  I do have plenty of
> Unibus machines and RK05s, most with vintage cables, but I'm sure
> several of them have crimps and dings and might fail close inspection.

My choice of 2 60 pin connectors vs a larger number of smaller connectors
was routability on a 2 layer board.  I wanted to make it as simple as possible.
With 2 60 pin connectors, I can keep the signals going from the edge connector
to the ribbon cable connector all on one side.  I’m mostly worried about
signal integrity.  If this doesn’t work to my satisfaction, I’ll probably go to heavier
traces and put in some ground planes.

I have a PDP-11/40 with 128KW of core.  64KW of that core is in a second
BA11F chassis in another rack.  I’ll be using that system (running memory
diagnostics mostly) to test out the cables.

I’ll have to work up some prices but I would expect it to be in the $100-$150
range.  I purchased a 100’ spool of 60 conductor ribbon cable and was agast
at the price.  I was originally thinking twisted pair ribbon cable until I saw what
100’ spool of that would run and decided to try just the straight “grey” ribbon
cable for now.

TTFN - Guy

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