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SCELBI
Just watched the video on the SCELIBI boards available. Is there a serial port to connect to a terminal?
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RAM for Apple 1
Where did you find some ram for the apple 1?
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Paul
Jan 14
Nice. Where did you find the 2519b shift register for less than $100. Also, is the CM2140 already preprogrammed too?
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Slow but unsteady progress ;)
There's been a lot going on the last couple of months, but I've been incrementally approaching a (hopefully!) working Kenbak-1. The wiring job is done, and am now about to start bringing up the electronics:
The front panel wiring was a pain... the 26AWG solid-core wire that Artem had supplied just didn't work well with my strippers and crimper, and kept breaking. I ended up switching to 24AWG stranded and also upgrading my crimper, which went a lot better.
Next steps - test the clock generator and start installing and testing logic.
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jim-kbk
Jan 12
I had a quite decent Paladin crimper but the die only has 24-30AWG and 18-22AWG slots, so it was kind of a case of either too small or too big. I wasn't able to find a better die so I bought a relatively cheap crimper that has 5 slots covering 2 wire sizes each.
I put in the fans with "an abundance of caution". They're not very noisy but I can disconnect or dial them down if I find they're overkill.
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BOM/parts list
I know the original magazine articles have parts lists and schematics, but are there any modern/cloud lists availble? Perhaps with digikey/mouser links and part numbers?
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Artem Kalinchuk
Dec 06, 2024
Nothing that I'm aware of. My goal was to use 1970s parts instead of modern DigiKey/Mouser parts although some parts did have to come from those sources. Any specific or hard-to-find parts that I used in my build were included in the GitHub page: https://github.com/kalinchuk/don_lancaster/blob/main/tv_typewriter/README.md
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New cases for the Altair 8800
Hey,
For anyone interested in building an Altair 8800 replica you'll need a case. Until recently Mike Douglas had been producing theses over at https://deramp.com/. Unfortunately after doing them for almost a decade he recently decided to stop.
The good news is that Chris Davis of https://adwaterandstir.com/ seems to have picked this up and is making Mike's cases again!
If you need one you can get one here https://adwaterandstir.com/product/altair-reproduction-case/
Mike still produces a front panel set and controller board that is S100 compatible here https://deramp.com/altair_8800c.html
So it is possible to build a full S100 replica of the Altair using this case.
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rm5150
Nov 30, 2024
This is fantastic news! I stumbled upon this forum & post after ordering the TVT boards. I immediately preordered the case from adwater, and had previously bought the altairduio kit. earlier this year i had emailed Mike about the case and got the reply he was no longer making them. This week I will call Mike and order the circuit boards.
I have an IMSAI (which required some repair) and a CompuPro S100, so I'm familiar with S100. Building a modern one will be fun.
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Output port not working
Hey,
So following on from my earlier post regarding some LS logic ICs not working in my Mark-8. I think I may have an issue with the 74LS75 latches that I have.
Firstly they seem to work fine on a breadboard test circuit. I can get them to latch data without any issues.
However if I input the test program on page 9 of the construction guide and run it the display shows this:
Rather than counting up on the output port bit 3 gets stuck on and all the other bits show very brief flickering.
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Artem Kalinchuk
Nov 03, 2024
Wow, that’s awesome! Thanks for sharing the details. I don’t remember having to add a pull-up resistor but I think it may be a difference between using the LS version or not. It might also be different depending on the manufacturer, which is why there are other areas in the computer that needed fixing of floating inputs but appeared to work for Jon without pull-up resistors.
In essence, it’s a good idea to tie all inputs to something and not leave them floating, otherwise you might get strange outputs.
Great work!
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Problem LS ICs on my Mark-8 Build
Hey,
I have been building a Mark-8 Minicomputer since early this year. It has been taking me a long time to finish as I have a number of retro computing projects on the go and don't work on the same project all the time.
Another issue that has delayed me is having to deal with LS logic ICs that don't seem to be happy to work in the Mark-8.
For example here was my first pass at the CPU clock:
Yes, you read that right 4MHz and yes a very messy sine wave. Also you will see that both phases of the clock are in sync.
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Artem Kalinchuk
Oct 28, 2024
Very nice write-up! Thank you for sharing your findings and insights. I think I used LS chips for my clock and it appears to be working fine. It may just be some bad chips.
Finding issues with the build is not always pleasant but it encourages the builder to dig in and learn about the inter-workings of the computer, which is a plus.
I have to say, your computer is looking amazing so far!
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Slowly coming along.
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jim-kbk
Nov 13, 2024
$202 including shipping. That's more than pcbway estimates, but after looking at reviews I felt that a specialist in front panels was the least-risk option. The fan cutouts on the back accounts for $33 of that :/
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Resistors!
I got a little obsessed with finding some period-appropriate carbon composition resistors. I tried various sources, even ordered some that turned out to be the more modern peanut-shaped style.
I eventually discovered that a Japanese company until recently made some quite satisfactory ones (until they were bought by Ohmite), and you could still find those via audiophile sources, as well as some NOS Allen-Bradley stock.
I got these via a Canadian company :
https://partsconnexion.com/resistor-carbon-composition/?_bc_fsnf=1&Watt=0.25W
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I just checked and now I'm getting "c\r\n >"
So a c, a new line/carriage return and then a space before the ">"
It seems to be working overall, so I haven't bothered to debug it.