If I were going thru the trouble, I'd want build a TX-0 clone!

On 2015-Jun-23, at 12:27 PM, Rod Smallwood wrote: The physical layout concept is actually quite similar to Harry Porter's relay machine: http://web.cecs.pdx.edu/~harry/Relay/index.html

On Tue, 23 Jun 2015, Phil Budne wrote: I think it would me more interesting to build a replica of a pdp-8 straight-eight using significantly-reduced flip chips with surface-mount parts. -- David Griffith dave at 661.org A: Because it fouls the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail?

remain of four. chip). At least two people are building PDP/8E type machines from TTL... http://www.vintage-computer.com/vcforum/showthread.php?47755-Build-your-own- PDP-8I-Part-2&highlight=pdp8%2Fe Dave G4UGM

Of course. The only reason a PCB backplane would be an issue is if there are signal integrity concerns, but at DEC speeds that?s not going to be a problem. Especially if what you?re aiming to replace is wire wrap which is in general worse at signal integrity than PCB. Now if you were looking to replace the chassis wiring of a 6600 with a PCB, that would be a different matter, then you?d want to be a bit more cautious. Even then it?s clearly doable, if you use transmission line design on the PCB signals. paul

From: David Griffith: Thursday, June 25, 2015 4:16 AM I've laid out a few of DEC's backplanes as PCBs before, mostly for the later designs that use both sides of the edge connectors. They tend to require about 4 signal layers. It can be helpful to bus power separately (using wire much as was originally done), and to route on the diagonal, as the funky sockets have larger chaseways in the diagonal directions. Also, the device is relatively high current. Some of my earlier attempts used trace widths that, in retrospect, weren't wide enough (especially power traces), trying to keep the number of layers down. I can't particularly recommend the original backplane form factor. They are all based on a 1/8 inch grid instead of the industry standard 0.1 inch, and not at all easy to find or inexpensive these days. From: Pontus Pihlgren: Thursday, June 25, 2015 6:39 AM Agreed. 6 with power and ground planes might work well, too. To my mind, the obvious choice for a new edge connector would be 0.1" headers and sockets. They are easy to find and produced by the millions, which means they are also relatively affordable. The only other concern I've had during my thought experiments along this line related again to the current/power involved. The device is likely to become difficult to cool if you achieve a 4X volume reduction. Oh, and I guess the nightmare of soldering many thousands of surface mount discretes and transistors to manufacture such a thing. Vince

From: Doug Ingraham: Thursday, June 25, 2015 4:10 PM I've been thinking lately that whole Omnibus cards could be generalized that way. I had assumed, since the subject contains "built from individual transistors", that something akin to the original straight-8 circuits was what was being discussed. Straight 8 signals typically run 8 mA when low and 10 mA when high, and that's from the -15V supply, per signal. I estimate that's a few hundred watts for the whole thing. Reducing the supply voltage to -5V would presumably cut the power (and hence the heat) to a third, by eliminating most of the waste heat from all the pull-downs. I like the 8/I too, though it's not "built from individual transistors". I completely agree, at least if you're actually going to use the darn thing a few hours at a time. Some models of the PDP-11 did use much smaller (still available) switches, but fitted them with honking paddles to make them more comfortable to use. Vince

On Wed, 24 Jun 2015, ben wrote: With 3d printers, it shouldn't be too much of a problem to make your own paddles at whatever scale is required. The only catch I perceive is which switch to use. I'm thinking of a fairly common slide micro-switch that seems to have been a Radio Shack staple for at least 20 years. -- David Griffith dave at 661.org A: Because it fouls the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail?

Yes, I saw that on The Register today. Pretty impressive. I think it should be called a DuellProcessor. :-) Regards Rob On 23 June 2015 at 16:22, Antonio Carlini <a.carlini at ntlworld.com> wrote:

That one's been around for awhile. Ever watch any old reruns of 60's era "The Outer Limits"? When there's a computer involved, it's clickety-clackety of relays working. Old TV can be fun. The other day, I saw an episode of "Get Smart" showing a bank of CDC tape drives, followed by a "Mission Impossible" episode where Mr. Phelps receives his instructions via 4-track tape cartridge (which self-destructs as usual). --Chuck

On 06/23/2015 04:11 PM, drlegendre . wrote: I seem to remember that the Packard-Bell PB250 used only about 400 transistors. (Magnetostrictive delay line memory). Lotsa diodes. So not totally out of the question, even today. --Chuck

On 06/23/2015 09:38 PM, Mark Linimon wrote: Ain't that the truth! --Chuck