• Please review our updated Terms and Rules here

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

Strip some of the wire and immerse the stripped end in some raw egg yolk for an hour or so. If it turns black, it's silver-plated.

However, almost all hookup wire that I've seen is simply tin-plated, although I do have some stranded solid silver wire. It wouldn't be suitable for wire-wrap, however--it's not nearly as malleable as copper.
 
Chuck(G) said:
Strip some of the wire and immerse the stripped end in some raw egg yolk for an hour or so. If it turns black, it's silver-plated.

However, almost all hookup wire that I've seen is simply tin-plated, although I do have some stranded solid silver wire. It wouldn't be suitable for wire-wrap, however--it's not nearly as malleable as copper.
Click to expand...
it will look like I am trying to use an egg as a cpu this evening! lol, thanks for the tip
 
Wirewrap reference

Wirewrap reference

From wikipedia:
A correctly made wire-wrap connection is seven (7) turns of wire with 0.5–1.5 turns of insulated wire at the bottom for strain relief.[1] The square hard-gold-plated post thus forms 28 redundant contacts. The silver-plated wire coating cold-welds to the gold. If corrosion occurs, it occurs on the outside of the wire, not on the gas-tight contact where oxygen cannot penetrate to form oxides. A correctly designed wire-wrap tool applies up to twenty tons of force per square inch on each joint.
Click to expand...

See http://en.wikipedia.org/wiki/Wire_wrap for the full article. It even has some pictures of classic DEC wrapped backplanes (PDP-8i, KL-10).

IIRC the PDP-8i has similar construction as you are proposing to do (except it used TTL logic IC based flip chips, rather than RTL/DTL/transistor based flip chips as in the straight-8 ).

I wish you the best of luck, it will be really interesting to see how this turns out. You have bitten off a very difficult and tedious design to clone, and trying to do it with salvaged parts from other vintage era machines makes it an even harder prospect. I have a couple of PDP-8m omnibus machines, and keeping those going is enough of a chore.

Don
 
I picked up some old computer books when I was at college, and I think one was for programing the pdp8 but I cant find it, bit I did find out that as my PDP8 will be made of transistors it is classed as a second generation computer and will have the job of a third generation computer in the would of the fourth generation computer!
 
Lou - N2MIY said:
This is going to be so much work, you should not skimp on the wrap wire. You should spend the money and use silver plated wire. You see, the silver promotes good contact where the wire is squeezed against the corners of the wrap posts. The pressure there is extremely high and the layer of silver "flows" nicely to ensure a high quality contact that will stay low resistance for a very long time.

Here in the US, even the wrap wire sold at RadioShack (like Maplin in the UK) is silver plated. (And I use RS wrap wire...)

Lou
Click to expand...
I think with the pack planes that have been soldered, I should wire-wrap and then solder, as the old solder it soft, and the solder may move under the wire wrap wire. I now have to find a lot of wrapping wire and tools.
 
Last edited:
rorypoole said:
I think with the pack planes that have been soldered, I should wire-wrap and then solder, as the old solder it soft, and the solder may move under the wire wrap wire. I now have to find a lot of wrapping wire and tools.
Click to expand...

Why? wire wrap and soldering are two different ways to do it. No need to mix them. If you have bad solder joints, simply re-solder them (yes, that will be a lot of work too).
 
some of the back planes will be recycled, and will have been soldered to a pcb, that I will remove, but may not wire wrap well after, as I will not be able to get all the solder off the pins.
 
Last edited:
Just catching up on your brand of madness. I think my approach of using ICs in place of transistors is more practical for the H200 as it must have a lot more gates than the PDP8 -- and they are Honeywell ICs from the 1960s, so justifiable alternatives. I wouldn't relish making an entire machine with transistors. In due course I'll put some stuff on my website to show the evolution of the Honeywell 200 logic from very simple transistor circuits through to primitive ICs as I understand it so far. All the evidence points to the ICs being virtually the original transistorised designs set in silicon leaving just the capacitors on the outside, so they were evolutionary rather than revolutionary.

On the wire-wrapping front I had enough of using a hand tool after unwrapping thousands of connections to strip down the backplanes for reuse. I later acquired an electric gun to do the wrapping as I also suspect that it makes a tighter more reliable joint than hand wrapping. Also it is essential to get the right sized bit for the particular wire and posts that you have to ensure a good connection. I'm getting my supplies from Farnell and yes, they are expensive. One big advantage with wire-wrapping is that I can hook up trial circuits and dismantle them again very easily; the other is that it doesn't bring on my sinusitis like soldering. Good luck.
 
I dont want to use IC's in the main pdp8 or memory expansion, except for the liner power supply regulators, but I will happily use IC's in the I/O expansion and floating point coprocessor, that is my brand of madness. lol
so far the backplane is in the research phase
 
Quite the reverse of my approach. Despite using logic ICs, which I know to have been part of Honeywell's 1960s arsenal, I'm avoiding using IC voltage regulators at present and meeting the PSU requirements with just diodes and transistors. When I get back to the Science Museum archives I may discover what they actually used. A floating point coprocessor sounds impressive; in the H200 even multiplication and division were optional features, but then it was never intended to crunch numbers, just tot up company profits. I/O was its speciality though and I haven't even thought that far ahead yet.
 
rorypoole said:
would you Science Museum archives have info on the pdp8?
Click to expand...

Yes. The documents are actually in the ICL archive, which is now lodged in the Science Museum archives located on a disused airfield at Wroughton near Swindon. The catalogue for the ICL archive is online and you need section 50 here: http://sw.ccs.bcs.org/iclarch/arch50.html

Digital documents are in section 50/4 on that list and cover the PDP machines and their software. Documents aren't allowed out of the archive, so you have to visit and read them there but they do provide a photocopying service which includes mailing the copies to you. The Wroughton archives website is here: http://www.sciencemuseum.org.uk/about_us/collections/science_library/visit_library_wroughton.aspx You'll have to book an appointment to go there and tell them what you want to see so that they can get it out of the stacks, which are extensive and not open to the public. When I went I emailed them a list of all the documents I might want to see, about twenty in all. If you visit make a day of it and take a packed lunch as there's no food provided on site and it is miles from anywhere, being in the middle of an airfield in open countryside.
 
thanks for the info, it will take some planning as its too far for me to do in a day and have much time there as I dont drive, what is the cost of the photocopying service?
 
rorypoole said:
thanks for the info, it will take some planning as its too far for me to do in a day and have much time there as I dont drive, what is the cost of the photocopying service?
Click to expand...

The photocopying charge is about the usual fee at a library. I think I paid around 25p per page in 2010. It's best to go there and choose which pages you really need copied. My wife and I combined the trip with a short holiday in the Cotswolds. You really need at least an overnight stay. As they say, if you don't have a car it takes 25 minutes just to walk from the main gate across the airfield to the archives and the airfield itself is out in the sticks.
 
Sorry, I think you are mad.

This is quite definitely NOT the project to start learning to do wire wrapping. I installed telephone exchanges and after a few million wire wrap terminations even I wouldn't bother. The trouble is you can't identify a naff joint. In the exchanges we used Gardner Denver wrapping guns, using 21 swg or 0.5mm wire. This gave a correctly tensioned joint that made a gas tight seal at every corner, your hand wrap tool definitely won't manage this.

Think of something else, Speedwire is by far the best but not made now, but try the Road Runner wiring system. I have just bought some spools of the wire, to make a core store, so still around. But wire to a socket, not the chip. The downside is that you need a very hot, 400C, soldering iron to burn through the insulation, and it smells something rotten.

An alternative might be PCBs, you can get cheap routers that will route a PCB, not etch it. The design software is available from many sources. A router might cost £1000, but how much do you think the wire wrap solution will cost, in the end?

Bob
 
maybe the project is a bit crazy?
when you say you are making a core store and you making some core memory?
I am not sure the Road Runner wiring system would work for the backplane, as it need 24 awg wire as it uses a far amount of power! but it could be useful on the flip chip boards

I dont want to replace the wire wrap on the back plane with a pcb, for one thing would be a very big pcb or pcb's and I think it is a vital bit of what makes the pdp8 the pdp8 straight 8.

and its not a bus system like ISA or PCI so would probably be hard to replace with a pcb?

woodchips said:
Sorry, I think you are mad.
maybe the project is a bit crazy?

This is quite definitely NOT the project to start learning to do wire wrapping. I installed telephone exchanges and after a few million wire wrap terminations even I wouldn't bother. The trouble is you can't identify a naff joint. In the exchanges we used Gardner Denver wrapping guns, using 21 swg or 0.5mm wire. This gave a correctly tensioned joint that made a gas tight seal at every corner, your hand wrap tool definitely won't manage this.

Think of something else, Speedwire is by far the best but not made now, but try the Road Runner wiring system. I have just bought some spools of the wire, to make a core store, so still around. But wire to a socket, not the chip. The downside is that you need a very hot, 400C, soldering iron to burn through the insulation, and it smells something rotten.

An alternative might be PCBs, you can get cheap routers that will route a PCB, not etch it. The design software is available from many sources. A router might cost £1000, but how much do you think the wire wrap solution will cost, in the end?

Bob
Click to expand...
 

Attachments

  • backplanes.jpg
    backplanes.jpg
    94.5 KB · Views: 1
  • pdp8a.jpg
    pdp8a.jpg
    93.7 KB · Views: 1
  • pdp8b.jpg
    pdp8b.jpg
    97.1 KB · Views: 1
Last edited:
The fire needs fuel to keep it burning!
Thanks I have seen both, I love it that there are people out there putting the thought and work in to build computers from scratch, its great, the would needs more crazy projects like that!
 
You must log in or register to reply here.
Back
Top