Exploring 1950’s Computer Logic with the Bendix G-15!

We’re back on the Bendix baby! In today’s episode, I want to take a look at all the unique logic cards in the system, but before we get that far, we gotta get our clean on. Hop along as we take every single card out of the Bendix G-15, clean each one painstakingly, then repopulated the whole machine, and finally take a deep dive into what each card does. We also try to answer a pretty important question – is this an NC or an ANC machine?

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

Thanks for watching!

Chapters
0:00 Working on the Big Blue Beautiful Behemoth
1:00 The game plan
3:25 Taking every card out
5:58 If you’ve got time to lean, you’ve got time to clean
7:56 Door latches and modifications
9:18 Putting it all back together
11:04 D2 “Diode 2” module
11:56 Card edges and replacement diodes
12:48 D1 “Diode 1” module
13:35 D3 “Diode 3” module
14:20 The BI and FF cards
15:36 BI “Buffer Inverter” module
16:39 FF “Flip Flop” module
17:12 And aside about diode clamping
18:05 DC “Diode Clamp” module
18:35 CC “Clock Clamp” module
19:42 CF1 “Cathode Follower 1” module
20:54 CF3 “Cathode Follower 3” module
21:23 CF2 “Cathode Follower 2” module
21:54 RA “Read Amplifier” module
22:44 WA “Write Amplifier” module
23:42 RC “Read Clock” module
24:44 Alphanumeric (ANC) vs. Numeric (NC)
28:44 Scouring schematics for the answer
32:49 What did we learn?
34:57 Happy kitty!

Here are all the modifications:
Blue
B3T - C7K
C8K - K5P
C7N - A54P
C7V - C8V - A54A
K34J - Loose wire
B54P - Two white wires that disappear into loom

Red
C7C - E48R
C7P - F51P
C7R - B36F
D16D - C54R
D16E - D35V
D16F - J15B
D16S - D17R - E14B
D17E - A28T
B41k - K47V (Broken connection)
B41V - H50P

Yellow
K7D - D30S

[robertfriedman]

This is the first computer that I learned to program. This was my inspiration to learn about computers. I had a long career designing computer hardware and software. I will never forget as a freshman seeing this computer function. I was so amazed at watching a typewriter print by itself. At that time, I was a freshman in electrical engineering at the University of Delaware. I programmed in a language called Intercom 500. It looked like today's machine language. UofD within a year replaced it with an IBM 1620 where I extensively used Fortran for any programming needs for my entire college career. In my last year of college, UofD had an SDS 9300 scientific computer which was infinitely faster than the G-15. SDS, Scientific Data Systems. Thanks for this video, it was great. I never did see the inside of that computer. By the way, I seemed to think that the typewriter was an IBM Selectric with a rotation ball but it is possible I am wrong. Maybe you could see if that was an optional typewriter for this computer. I do remember that it had a rotating drum for memory. My first experience with the G-15 was in the fall of 1961,

[murph]

i find it hilarious that their idea of "buffering" was just "amplify and crank that shit up to wumbo so that anything less than a lightning strike won't degrade the signal"
this is absolutely fascinating, subbed for more

[CuriousMarc]

The best way to clean the exterior is to retr0bright it! Just kidding. Don’t you love that initial detective work that draws you to the internal minutiae of a seemingly incomprehensible machine. And when you finally unravel the mystery it’s immensely satisfying. Superb cleaning and first inspection job.

[atkelar]

The tape reader unit shall always look like a coin slot mechanism to me... "Please insert 25c for the first 100 clock cycles!" 🤣

[ruawhitepaw]

That machine was built 30 years after the advent of broadcast radio, and the start of the electronics revolution. Meanwhile, we're now 70 years since that machine was built...

[mikefochtman]

On the bright side, removing and reinstalling every card has probably 'wiped' years of oxide from the connectors, eliminating one source of faults. (we had some edge-card machines from the 70s, when in doubt 'reseat the boards' lol )

[socks]

I clean 45 year old machines daily at work and your technique is spot on! I combine the paintbrush with a hepa vac and use a little contact cleaner around the electronic bits and stubborn gun from wearable rubber components, doesn't seem to take off paint! Otherwise I am new here and I love the content, I'm sure the original engineers would love to see their work getting this much appreciation. Thank you!

[gcewing]

I think there's a bit more going on in the buffer-inverter than just 3 inverting amplifiers. The second and third tubes share a cathode resistor, forming a Schmitt trigger. That would help with producing sharp output transitions.

[jamessmith]

My high school was donated one of these for us to explore computers and programming. I am now retired after 40 years as programmer/analyst for mainframes, minis and microcomputers. What a happy circumstance for me!

[joysticksnjukeboxes]

What a herculean task; you're amazing! BTW I love that crinkly paint finish that you just don't see anymore.

[janno]

I still think the computer has a coin slot.
Haha.
Wonderful video, it was an honour talking with you while you were cleaning the cards

[ristopoho]

Watching you clean that amazing machine does make me feel like i should clean some electronics too. Don't have vintage things around right now so a microwave will have to do. My friend said it looks filthy... Also the fridge..

[brianstuart]

I've always loved this machine, and the more I learn about it's designer, Harry Huskey, the more impressed I am. He was arguably the most influential pioneer that few have ever heard of. I'd be lying if I said I wasn't a little envious of your opportunity to work with it. I look forward to future installments.

[ReallifeBambiDeerattheFarm]

An old computer with thick cabling and connectors with hundreds of pins in them. 😊! Will ❤ seeing that old Bendix running again!

[bobanalog]

22:23 I've seen flippers (flipflop) used as Schmitt triggers for pulse reforming. It looks like that's what they're doing here. (maybe?)

[olddisneylandtickets]

This is amazing. That typewriter interface with the relays and 10/5 bit conversion, mind blown...

[gunnar_langemark]

I came to your channel after seeing a link to you, in a discussion regarding punch tape. I have now watched dozens of your very interesting videos.
I realize this is more than a year old, but I will point you to the expertise of those interested in old typewriters. You'll find them here on YouTube. Knowledge of how to clean and (not) oiling old mechanical machines and how to clean without damaging paint is on a high level.
Your channel and your approach to your machines is fascinating, entertaining and very interesting and educating. Thank you for that. My own hobbies has included cleaning, reparing and restoring old manual typewriters, reel to reel taperecorders, electrical guitars, amplifiers, laptops and stuff like that. So I'm watching your work with a great interest.

[StoneyK]

With regards to the typewriter it appears to be 'universal', there was a printed label on it saying only to connect to either NC1 or ANC2/ANC3 machines. Which makes me think that it does support numeric-only machines natively, and perhaps the relay box is only used for ANC1 machines.

[stitchfinger]

the design of this machine is simply enchanting
thanks as always for sharing your cool stuff with us

[StoneyK]

What I find most mind-boggling is that the processing power of these massive machines is literally dwarfed by anything that is the size of a grain of sand and costs a few cents today. That's probably the most important reason to keep these machines conserved and running: To teach our kids how computers started and were developed.

Children from today take computers absolutely for granted, and it's kind of important that these machines were designed to save lives, namely, to win wars and protect us against threats from enemies.