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

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,

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

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

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...

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.

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

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

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!

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

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.

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..

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 )

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!

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

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.

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.

The read amplifier looks simple enough to me. The clock pulse on the right resets the flip flop and the read clock will sample the read head signal to determine if the flip flop should be set. It's roughly equivalent to a D-type flip flop. It's to avoid stray pluses on the read head causing a ripple effect though the machine.

What an amazing machine. I started on computers in the late 70's with the TRS-80's, and had no idea how complex computers were from the 50's. Thanks for sharing.

AMAZING that this machine worked at all. With SOOOOooo many ways for it to fail!! All those connector cards. Thanks for this video. This really shows how far we have come.

Old style resistors brings back memories when I savaged junked tv and radios for my electronics projects.

WOW. 4:30 That's a lot of cards, but they look awesome laid out like that.

It's so cool that you are going to try to get this machine running! The Kinkaid School in Houston acquired a Bendix G-15, serial number 186, in 1969. It was donated by a local engineering company and formed the nucleus of the first computer club. Unfortunately, over the next two years it became increasingly unreliable and the students in the computer club found themselves spending most of their time troubleshooting and repairing it. I entered ninth grade in 1971, too late to ever see the G-15 in operation. We used an ASR-33 to dial into a timesharing service instead. I was always fascinated by the old machine, which was still sitting silently in the corner of the room. I hope you get this one running!

Love the level of detail - I won't say I can follow the intricacies - but its fascinating to see these older designs up close. Thank you

Looks like the read amplifier does pulse/edge detection on V1A. The trim pot sets the transient sharpness treshold. V1B gates this signal to the flip-flop on negative read clock, and then I guess the flip-flop is then reset by the clock. In short, it detects any asynchronous pulse by the transient edge, and converts it to a digital pulse synchronous with the two clocks.

This, along with your other videos, encouraged me to visit System Source this weekend for their repair and boot sale and open door to the museum, where I met Bob Roswell and was taken around the place. What an amazing museum he has set up! Bob is an incredibly generous person that was wonderful to visit and talk with, thanks!

The shot of all the modules and boards arrayed out is great and a really rare thing to see, thanks for taking the extra time to set that up.

Great video. The crinkle paint you have to be extremely careful with. Some become gooey over time and using the wrong product could remove the paint. A test with Dawn dishwashing liquid, water, a non-abrasive cloth, and testing on an inconspicuous place would be a great idea. At a planetarium I worked out in the late 80's, had a Spitz 512 digital planetarium projector and the projector and the control console used the crinkle paint and we were warned by Spitz that the crinkle paint could be a problem, as they had issues with one particular paint manufacturer's product during production. They recommended only soap and water and gentle pressure cleaning. There was no Dawn Ultra back then, just the regular old Dawn, which may still be manufactured. I remember seeing it at a dollar store a few years ago.

Watching your videos while working is very motivating: Seeing the problems you have to solve in this old beasts makes me realize this compiler error I am getting is not that bad after all.

Wow! That thing is amazing! Thanks for explaining the different cards. Things are so different today.

0:48 Seeing an Xbox 360 in a vintage computer museum hit me in a place I didn't know could hurt

Classic. A lot of early computers used diodes for the logic, and the tubes or transistors were only there to boost the signal or boost and invert the signal. I mean there was an entire class of logic chips that people tend forget about (or just not know about entirely), and that's DTL, or diode transistor logic, the precursor to TTL. I might be wrong, but i think the Apollo program computer in the lander was built using dual 3 input nor gates, using DTL. Some of the first digital IC's made. Again, could be confusing my history, but it's interesting nonetheless.

I'm not super familiar with vacuum tube Electronics, but from the schematic you showed for the read amplifier card, it looks like it's an edge triggered monostable. Meaning that on a rising or falling Edge, depending upon how it's wired up, that circuit will generate a single pulse on the output of a fixed time with. That's why you see the Transformer coupled input driving a flip-flop. The Transformer coupled input makes it so that you will only act upon a rising or falling Edge, again depending upon how it's wired up, and then the flip flop is made so that you can with a single input trigger a single pulse on the output..... at least, that's what it looks like to me. For what it's worth.

Cleaning the wrinkle-finish paint on the outside should be easy: You can use a mild detergent and a toothbrush to work the dirt loose, then wipe it clean with a soft, lint-free cloth. Thanks for the fascinating look at this beautiful machine!

u-z is only one such notation, there were more than a few, and had to do entirely with mapping onto given keypunch and teleprinters in a particular setup. ;)

its amazing how much have improved from the 70s, that is a computer... i dont want to try and poke around the the ui though. It seems complicated. Love the hand made cards that populate the machine. that is pure skill and no cheating.

Regarding cleaning... i use a particular bar soap that's in the hand soap section when I need a soap that rinses clean with tap water, it's Kirk's unscented castile soap. You can either dissolve a little in one container and have a second container and sponge for rinsing, or just rub the cleaning implement (brush/sponge) on the bar itself once it's wet. Does a remarkable job removing "regular" gunk and grime.

If the signals exist in the machine, maybe you can bring them out to the cannon connector. Good luck!

I find the best way to clean industrial crinkle and hammered paint is just to get in there with soapy water and a brush. Kinda like cleaning textured vinyl and such. Anything like polishes and such just leaves a white residue that you end up scrubbing out with soap and water or naptha and wishing you had just done it that way in the first place!

This kind of stuff is always neat to see......... I restore stuff too, but not old computers. My style is to restore things I can actually still enjoy using... and Old school computers aren't my fun zone. Much respect and good luck on your quest.

I've been watching your channel with endless curiosity!

Oh! This is a question I can actually answer the weird indexing on the schematics pertains to how they are indexed in the real world for the technicians. The schematics had to be professionally printed. (Mimeograph is a few years out still) they index that way because multiple copies were likely stored in a physical index so that if you were going on a service call you could pull just the copies you needed (and then return them.) There was also likely a printed book but that was more or less likely indexed based off the drawings id (as that would have been produced by the designers)

The traces on those cards are a thing of beauty!

(@4:13) You doing the fast-forward there if you pulling out the circuit cards reminds me of the ST:TNG episode where Data gets “drunk” and pulls out all the isolinear chips from the main engine computer. LOL. 😅

I`m glad I found your channel. I could not wrap my head around the use of tubes. It still hurts, but not as bad any more. To think that in the 1950`s they figured this out. I can only wonder what they would think about electronics present day.

I very recently visited the Computer History Museum in Mountain View and it felt like watching your videos

Fun Fact: multimeter leads; A female 4pin molex pin can be used a to connect to the end of a standard multimeter probe so you can make custom multimeter ends (I made a pair of alligator clips for mine)

Some of Beta Iota Tau at Rose-Hulman found a G-15 in a basement (I forget which building, this was late 1970s!). And we actually got it working!

On the Amiga, the Bus Error signal is called BEER instead of BERR. I guess for the designers, it meant "Let's have a break and think about this. Again." So what is that POOP? "It's spilling out random sh*t at the other end"? 🤔

Your video production quality never ceases to amaze me

Man, that's a beginning of a great new saga !! Wish you the best of luck. Will be anxiously following the developments. Godspeed !!!!

I wonder about the wisdom of taking all the cards out at the same time. Yes they are keyed, but like the backplane, there might be cards with modifications on them. If you don't realize/miss this, you might not put it back in the same place and you might have a difficult mistake to figure out. Some of the tube modules had stickers on them that again might not make sense in any other place than the original one. Better to take them out one by one and replace them before moving on or at least mark every single one so it goes back where it sat. That said, it's done by now :). It will be very interesting to see it progress.

Clean always seems to make stuff run better.

I think, the conversion of this machine to alphanumeric was started, but never finished before putting it out of service.

That crinkle paint looks like the same kind used on some typewriters in the '40s and '50s. I have a typewriter or two with that sort of paint, and I generally use Windex or Simple Green to clean those. It's worked quite nicely for me; they seem very forgiving on paint.

E excellent work! Thank you so much for sharing the restoration.

I love that crinkle paint from that era. I was reading up on it a couple of years ago, & it turns out that it's just ordinary enamel, & the unique texture is a result of cooking it dry very quickly. TL;DR: Windex & a stiff (nylon) brush should make short work of getting the dirt out of the crevices, followed by a thick, damp towel.

After pulling out the cards, I would have taken the opportunity to do some continuity checks on the card slots, and checked them off against the wiring diagram. That is, if you hadn’t “painted yourself into a corner” there by the pinball machine! This way you can note (& fix) any bad edge-connector pins, bad solder joints, or just dirty contacts. Doing it now will save time later, or you’ll be like Rainman Ray (Rainman Ray’s Repairs YT channel) when he says, “I love my job so much, I do it twice.” 😏

WOW! So much work to get this far... very impressive David! Well done, Sir!

All those beautiful Allen Bradley carbon composition resistors remind me of my early days working for that company.

I think, you do know that you're so into a project that you are comfortable to walk around in bare or stockinged feet over potential wire shards, solder drops, sonic electronic digital ball busters! We're talking electric splinters! Electronic lego bricks! I love to see that passion! But, in all seriousness, it does me the power of good to see you head down (down not crashed!), deep in the game, living and breathing this stuff! I can barely wait until the final result! My father was an NCO in the British army "Royal Signals", and he even served in the Falklands, setting up telegraphy and front line communications, even when under fire :-O Sadly, he had to leave the Army for health, but the deal he made was that he could finish his service whilst working for the British Territorial (aka Army Reserve) Army, still for the Signals corps. I remember he took me to the local HQ and showed me a machine that he promised me was a Computer, although it took up the majority of the space in the back of an Army Lorry! But even though I never did have a clue about how one might even use such a machine, I've always been impressed with "Big Iron"! So seeing you with these machines is a real treat! I know what you've said about emulation, certainly of the drum memory; but I wonder if there is mileage in documenting this system *for* emulation, whilst you're working hard to keep it real? Sad fact is, one day - there will be no more G-15s in a viable state - but wouldn't it be incredible to have a digital blue print to allow each iota of this machine to be replicated in code, to allow the dreams and the science to continue? For me, it's all about the inspiration of young (and old) minds! The "Lest we forget" factor ... And I don't mean for this to sound like complete Hyperbole, but I believe there is a lot of value in replicating such old systems, so inspire the new generation. I also think that there is still, somewhere, a use case for such "robust" equipment that might actually have a genuine and viable purpose for working as much more than just a museum piece! So, that's my little story - I will try and pump my Dad for more information about that computer and share, but in the mean time - thank you so much, again!

Those big round connectors used to called "bendix connectors". As an intern many years ago i was tasked with sourcing some replacements for a seismograph and it took me most of a day to figure out the military specification that they are now known by and order them from Digikey. Its cool to see them used on an old piece of Bendix equipment.

Absolutely fascinating! Thank you so much for putting yourself to the trouble of reporting your findings on this not quite yet laptop computer. I'm subscribing, I want to see more of this. Thanks again!

The best thing to do is makes some jigs and test all cards before powering up and trying to fault find on the G-15. It will likely be quicker to make jigs and know that all cards are good. The cards are so simple that if any fail, they'll take only minutes to diagnose in a jig, but in the computer it could take you days and days.

I feel like I'm starting to understand more of the construction of this machine, this will be fun to see progress from static display to computing computer.

11:04 and you just keep sneaking that shirt in there... I've started a playlist of these now!!! Ha! Seriously, you're making an already awesome video just WAY over the top for me here!

I sometimes use that Armor All spray cleaner for auto interiors to clean equipment. Cleans well and does not have the aggressive ammonia issue in Windex. So it is much kinder to markings on equipment. There are scented versions of this cleaner to avoid.

I have a bunch of those black-brown-red germanium diodes I got in a box of old electronic parts, and I could never find any specs on them. It's good to finally know where they came from!

The king of the nerds is back on task with the Bendix G-15. Yes! This series is going to be epic. Well done and thank you!

This is your best series so far. Love it

I'm really excited for this project! What a cool machine. I didn't expect the cards to be so loose in the slots, but seemingly it's not an issue.

The first computer I ever had to service was an analogue computer, with valve (tube) amplifiers. It ran a flight simulator😊

Wow so with all the cards laying on the floor .it looked just like a magnified shot of a modern day chip

Should imagine that the purpose of the S-R flipflop on the read amplifier is to hold the data read in in between clock pulses, the transformer would provide the amplification stage,

Of the gadgets you have this one is the most curious for me…love it to death!

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

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?)

Super exciting, I can hardly wait for this machine to work.

Looks to me like the typewriter can be used with ANC 2 or ANC 3 so your machine may have mods that convert the NC1 into an ANC 2 or 3... ☺

thanks for the amazing quality video. very entertaining, and educational.

This beast is impressive and I reckon it would survive a huge EMP not like our micron thin chips in modern computers. I will watch with interest for further progress.

@5:00 That would heat the house for sure. Great channel. 😊

I was actually glad to see that the card edge connectors were double-sided but single-circuit, since it makes them a lot more reliable. But it still would be a daunting task to clean every one of those connectors if they get oxidized. I really like the modular design though. It seems like you could make test jigs and test all the cards on the bench without too much trouble. Looking forward to the first power-ups! Take care with those capacitor banks, and definitely use a variac and some current limiting if possible. This will be a really fun series.

I was a Field Engineer with Bendix in the 1970s. I was in the airborne sonar division at Sylmar, California. We had a computer system used to run Acceptance Test Procedures on sonar that was mounted in SH-3 Helicopters. The computer was a beast. It weighed 55 pounds and was quite large. Back then there were components that were so large we had to solder them with a soldering gun instead of a soldering iron. Ah, those were the days.

10:00 Putting the cleaned boards back into the system reminds me of the scenes from Star Trek TNG when they used the isolinear chips in the computers. Also I'm glad to finally hear the difference between "numeric" and "alpha-numeric". I've only remember Alphanumeric being the catchphrase of Enzo on Reboot.

I bet that relay box sounds awesome when in use!

The 1950's was a time before static was a thing.

Fascinating journey of discovery! The wrinkled paint finish is known as Raggrinzante, and a soft brush with mild soap and water solution should help get the dirt out those ancient creases.

Usagi Roadmap: - Zuse Z3 - Programmable Loom - Abacus - Stone age pebbles - The turing machine that runs the Universe 😀

Fantastic computer. I can't wait to see those valves glowing

Now I want to know what the POOP signal actually does! Excellent work BTW!

System source is absolutely unbelievable. Take the trip.

To clean the krinkle paint surfaces, go the dollar store and get concentrated La Awesome, dilute it 1:3 parts water, and saturate a slonge with it. That has been the most effective for me.

You have to be very careful cleaning tubes - a lot of them are labelled with water-soluble paint than can wipe right off.

Yay, more tube computers.😆

Excellent work and lots of it! As for cleaning the outside case, I've used a bit of WD40 and a soft toothbrush. Once done, Windex to pick up any oils left. Hopefully, this helps. Thanks for sharing

Simply incredible.

I wrote my first code on a G-15 at UCLA Engr basement in 1960. OPs were numeric; I think '50' was multiply(?) No assembler - you assigned addresses for code and data. It had both paper tape and punch card I/O. Aside - down the hall was a comp called SWAC that created the sound for the movie "Forbidden Planet". The operator was entering code in binary to develop logic for a pseudo random number generator. It had a speaker hooked to the CPU so he could hear how long it took to loop.

Might want to buy some boxes of plastic razor scrapping blades so you can be more aggressive without going through the paint. Keep up the good work!

Man, I love your enthusiasm! It most certainly looks cool all laid on the floor. I have tubes only in my guitar amp, because my retro computers aren't this retro, just C64 & some Amigas. Your videos might lead me to dangerous path though 😅😅

22:00 I guess the part above the gudeman capacitor is the input transformer? The whole machine is a great example of old manufacturing. Early PCBs, but no through plating so they had to put an insert into every hole. The parts have their legs all coming out to the side for terminal strip or point to point construction, which leads to that for today odd looking transformer blob.