VTC P.36 – Logic Done!

Our DIY vacuum tube computer hits an insane milestone today – we finish up the logic! All that’s left after this is building out the paper tape and running code on it. We’re so close, so come along as we finish off the last little bits!

Ken Shirriff’s article on the MC14500:

Tube Computer Wiki:

Logisim file mentioned:

MC14500 Single Board Computer:

How I cut my PCBs:

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Intro Music adapted from:
Artist: The Runaway Five
Title: The Shinra Shuffle

Thanks for watching!

Chapters
0:00 The story so far…
4:06 A quick refresher
8:15 Hershey kisses of molten metal
10:46 Plugging in the easy stuff
11:40 Cathode follower buffers
15:25 Cathode follower buffers… again
17:42 Catho… I’m gonna stop you right there…
19:27 Blinkenlights!
21:50 Soft start
24:58 A massive milestone!
26:42 “My name is Sue! How do you do?! Now you gonna die!”

[chainqk]

This channel is worth watching just for the sheer excitement over a vacuum tube warming up.

[larryk]

You are the best at keeping ancient technology alive.

[pjcnet]

You've done so much in 2023 it's amazing you've found any time for this on top. It's great to see it almost complete, well done.

[wmrg]

Only need to build the paper tape reader...NO PROBLEM 😂

[ForgottenMachines]

4:08 Another Forgotten Machines Tshirt sighting! Thank you! What an amazing overview...So glad to be here, and so glad you're doing this and documenting it SO well in video!

[horusfalcon]

As I watched this, I got curious again about your methods of circuit board fabrication, so I went back and tagged your video about how you use a CNC mill to cut these out. I'mma go back and watch that again (it's been a couple of years), and see if I might be able to come up with a dedicated device for cutting circuit boards for myself.

I love the "steampunk" look of the UE-1, and the bench power supply you were using for this video (and others, I'm sure), and I'm looking forward to the video where you fire up the whole shebang. Be careful in the workshop and everywhere else, and I'll see you in the next one.

[nnsda]

It's taking shape nicely. Can't wait to see some paper tape going into it.

[DefaultFlame]

I am so looking forward to seeing it fully functional.

[SeanBZA]

If you are at all worried about that 1R resistor cooking up simple enough to crimp ( not solder, as that will kill it) a 105C one time thermal fuse to some wires, and put in series with the power rail. That will then be attached to the resistor body, simple enough by using a fibreglass sleeve (again heatshrink not usable with 105C melting it before it will shrink) for insulation, and then a simple fabricated clip using the grooves on the resistor to hold to the top. 105C surface temperature, and the thermal fuse will melt and stop operation long before that resistor gets hot enough to burn the wood or PCB anyway.

Commonly done on old TV sets with dropper resistors, though there it was often just a spring held with solder, so that if the resistor got hot enough, over 183C at the solder point on the spring, it would soften and the spring would open and break the circuit. Simple, reliable, and even if the resistor got on the way to red heat it would trip before it got hot enough to do more than start to smoke gently as it cooked the dust accumulation on it.

[theantipope]

6:47 lol! Thank you for incorporating the classic Signetics 25120 WOM chip data sheet. Very much a rarity in IC design, in that it includes a filament supply pin, making it perfect for your valve/tube computer. ;)

[jonathanwhiteside]

Incredible project, looking forward to it getting over the finish line.

[willjackson]

Hey David! Ever heard of M^2 logic, also called Mickey Mouse logic? It uses diodes and common CMOS chips to build lots of quite complex gates, potentially even oscillators or counters. Maybe it is adaptable to tube circuitry, and could simplify your design!
Look it up, if you already haven't!

I'm so excited for all this progress you're making! I can't wait to finally see the whole system together!

[lindoran]

I have been on a marathon iteration cycle on my homebrew computer I definitely understand how great seeing the finish line feels 😊 well done! I can't wait to see this finished

[jeromethiel]

The funny thing is, for most industrial controls, a lot of the work IS single bit. Ladder logic (AKA relay logic) is still to be found in a LOT of machines, even modern ones. Because for some tasks, a single bit is all you need. Granted, modern PLC's aren't using single bit processors, that would be silly, but a lot of the logic is still single bit.

So back in the day, i can easily see a single bit processor for industrial automation would be a smart thing to make.

[slaquers]

About a year ago I had no tubes, and no tube devices. Always been 'interested'. Anyway, a KG-635 oscilloscope, Jackson 607D HV power supply w/filament supply, grid dip meter, all vacuum tube powered and recapped by me - I now own well over 70 tubes not including the tubes inside my equipment. I also enjoy radios, so I have a old tube CB radio and some ham radio 'pieces'. Working now on a tube tester for 7 pin Soviet tubes. I have 40 6J1P, 15 6J1P-EV, some 6Z4's, OA3's, 6N2P's, and others. I've just started to experiment building circuits with the 120 volt 6J1P's. Anyway - thanks for all the videos I hope to see some more tube videos in the future from you.

[jaut-]

This was interesting to watch as the VTC comes together. I can’t wait to see how you make the paper tape subsystem

[KeritechElectronics]

Ha! Lovely. I wonder if you'll be taking it to VCF again. Lessons learned and hopefully no rapid unscheduled discombobulation this time. If so, I'd suggest sandwiching the boards together with rigid links between them, all electronics inside, protected from any outside objects.

[ForgottenMachines]

6:47 in many circles, "write-only-memory" is considered a joke, because supposedly there is no such thing, what would be the point! BUT, here it is, you've proven that it IS real...provide the DATASHEET to prove it, and you're demonstrating the use of it. Totally blows my mind!

[markhatch]

It's a Turing Machine! I will be fascinated to see what kind of programs you can write and run on your little system!

[melkiorwiseman]

Quoting Bob Cratchit from the Alistair Sim version of A Christmas Carol: "Another triumph!" 😄
BTW, you may have some ppl attempting to contact you via YT because I've occasionally been mentioning you in a FB group for old computer equipment. Whenever someone has some pretty old stuff and wants to find a home for it, you're the direction I send them in, knowing of your connections to at least one computer museum. Hope you don't mind. 😉