How do I wire wrap used back planes to build a pdp8 straight 8?

[Marty]

Hi All;
Rory, You mentioned that You are using the Backplane from a PDP 12, I would think that You would be Happy with that without distroying it and turning it into a PDP 8.. I just looked at what a PDP 12 is/was on the internet..
Or AM I misunderstanding both what You have and what You are doing ??
Also do or did You have the Boards (Flip Chips) from the PDP 12 or just the BackPlane ??
Just having the BackPlane and Flip Chips could result in quite an educational experience.. You could make any processor with any instructions that You would like to..
THANK YOU Marty

 

[rorypoole]

all I got of the PDP11 or 12 was the backplane parts, and the wirewrap had been cut between them already, if the packplane had been intact I would have used or traded it, and the flip chips I have are from ebay, I would not destroy usable vintage computer gear to make my PDP8, but I would trade it.

 

[rorypoole]

I have spent the last few days unwrapping the wire wrap on the used packpain parts, I now have a box of used silver plated wire and sore fingers! the set of crochet hooks has been very useful, but when I am done I will have 4 of the 5 and a bit packplain parts for the pdp8! and I have some pdp bus sockets in the post, I am going to see how much of thew used wire wrapping wire I can reuse!

 

[rorypoole]

the wire I have been taking off the used backplale parts is probably 30 awg, and the straight 8 used 24 awg, would it mater much if I reused the thinner 30 awg for all the logic wiring on the backplane except the power and ground? I have saved a lot of silver plated wire! and a shame to waste it?

http://homepage.cs.uiowa.edu/~jones/pdp8/UI-8/guide.shtml
under Unknown Logic

Or is it all too do with the right wire gauge for the blocks?

http://www.faqs.org/faqs/dec-faq/pdp8-models/section-2.html
(Machine wrapped wire-wrap technology was used on the backplane using 24-gauge wire.)

 

[Marty]

Hi Rory;
I think it all depends on Your own feelings about what You can live with.. I think 30 ga would be fine, it is used on my PDP 11/45.. So, I don't know about the Earlier machines, if it was a currrent thing or a maintenance thing.. I. e., thicker wire stays in place longer and makes better contact, might have been the thinking..
THANK YOU Marty

 

[RSX11M+]

Not being a PDP-8 guy, I had my doubts about this 24ga wire claim until I saw these photos of the U-Iowa machine.

It's also a great example of the wiring patterns.

I think the original wire-wrap technology hails from a U.S. Navy spec / requirement - it would be quite old. (Dad worked for Western Electric and was in the Navy - which is where that understanding must have come from) It's refined form was employed in mass production by Western Electric on Bell system components. I also have a recollection that the original concept did not require the ends to be stripped of insulation... the wrap pressure at the corners of the posts was to accomplish the connection by cutting through the insulation. The Bell system eventually employed with this same notion (no stripping required) with 66 and 110 blocks, where it gained acceptance.

24 ga has 2x the diameter of 30 ga, 4x the cross sectional area, and 1/4 the resistance per linear measure. I would think long and hard about how I'd feel if it were necessary to un-wrap and re-do. How would one even decide it was necessary?

Thinking about it a little more - I think the post size also matters... it may not be feasible to use 24 ga if the posts are too small. (the force required might sheer off the posts)

 

[rorypoole]

Today I received a load of dec parts, what is interesting is the H808 dec socket is meant for 24awg and the H8030 is meant for 30awg wire wraping wire, it is surprising how much bigger the H808 pins are, the used backplane pins are the same size as the H8030.
the straight 8 would have used the H808, the H8030 and the used packplane parts also have twice the pins as they are for later double sided flip chips, the extra unneeded pins on the newer DEC sockets will make wiring the packplane intresting!!!