(For those wondering: It looks like the oldest still-running digital computer on Earth is the 'Wolverhampton Instrument for Teaching Computation from Harwell which dates to the early 1950s and is at the National Museum of Computing in Bletchley Park.)

Bravo! Christmas a few days early! (Bob @ System Source)

I would suggest connecting the clock track to one channel and the timing track to the other channel of your DSO and capturing the waveform with the highest memory depth your scope supports. That way you have a backup that could potentially be used to recover it if anything happens.

Wow i did not realise this was the first computer Ken Thompson ever used. The change this machine made to the world is quite possibly incalculable, if its what got the guy who wrote Unix hooked

I had my first experience with programming on one of these machines back in 1964 when I worked at a weather station in the Marshall Islands. I programmed the computer to process radiosonde readings that had previously been treated manually. Can't wait for you to get that paper tape reader going!

Love the way you trace schematics. It makes it much easier to understand and follow power and signals through circuits.

The documentation is beautiful in its own way. What always impresses me about these vintage computers (even 1970s and 1980s home computers) is how rapidly they seemed to be developed from concept to manufacture without (obviously) the benefit of modern computers to assist in designing them and managing their development. A lot of talent and hard work!

The smoothness of those signals was awesome. What a beast of a machine.

Drum bearings try to pull the drum out, and get it on it's side. Then take the bearing facing up, and warm it up a little after cleaning, and apply some EP90 gear oil to the edge of the steel dust shield, to make a thin layer on the seal, and let the bearing cool down, which should allow some to enter past the seal, and mix with the old grease there and revive it. Leave overnight with it up, and next day clean off the excess, and turn so the other side is up, and do the same warm up to around 70C, and apply the oil, and allow to cool and pull some past the seal. Quick fix is to make a sort of dam there if not moving the drum, and fill with the oil, and leave the bearing half covered overnight, so it can seep past the dust shield into the grease there, and give it some lighter oil components again, and reconstitute it a little. Otherwise you need to gently pry the shield off, and then pack with a little moly based grease, and put the cover back on. Look for the same bearings, and order a cheap one, and sacrifice the bearing, using a grinder, to get the shields off them, and thus get new ones if you damage the old ones pulling them off. Have done this to a lot of bearings, especially where a new one was either not available, or needed a lot of specialised tooling not available to set the preloads, and the lube would get you another few years of running out of them.

Congrats David! That was probably the first time in decades the 'Big Switch' was thrown with power applied. I can't wait to see how the revival of the G-15 evolves. BTW, great meeting you at System Source when you did the drum swap. I'm they guy you borrowed the Swiss Army Knife from.

I appreciate your proper caution in the power-on testing. You are saving yourself much potential grief. Seeing the filament load decrease as each voltage step settles was fun. The heaters increase in resistance as the warm up and that causes the voltage to ramp betweek the steps. Do consider powering the DC supplies externally the first time and ramp up the applied AC voltage slowly to re-form the capacitors and limits any surge current from unforeseen faults. I know you will have already checked the resistance across the DC main busses as the first step. The ghosts of Engineers Past will be watching over you as you proceed 😀

I was a freshman at Rose Polytechnic Institute in Terre Haute, Indiana in 1963. (Since then the school name was changed to the Rose Hulman Institute of Technology.) Freshman arrived about two weeks before the rest. As we were on the guided tour of the “main” building, we walked by an enclosed room with a large glass window. We walked up to the window and peered into the school’s computer room. There, in all of its glory sat the school’s blue Bendix G15 computer. I had a class that taught us how to program the G15. Subsequently several other classes required that we create programs to solve problems. This series of videos is a trip down ancient memory lanes. Thank you so much. By the time that I graduated other hardware had been purchased; however the G15 was still being used. Sigh!

A simple and safe modification you can do to help preserve the clock and timing tracks is to put a ~470pf capacitor of any type in series with the read heads. This will create a high pass filter set at ~60khz. the timing signals should pass through unmolested while any dc bias created by a shorted tube or other malfunction will be blocked. You can verify this by probing pin 2 of the appropriate preamp tube socket before and after the modification. you ~may~ need to adjust the gain pot (R7 on the schematic) up a tad to compensate, but you just have to make the trace look the same before/after the modification. Worst case you'll lose 2-3 cycles of the track in a short. if you want to be extra paranoid you should be able to lower that cap to 220pf, and then it should be nearly impossible for the tracks to self-destruct; though there may not be enough gain adjustment left to compensate. Regardless, it's a simple modification with little to no risk and nearly perfect reversibility, should that be desired, but great reliability gains.

19:26 that's an amazingly clean signal, after over sixty years! 😍

The "bearing noise" might be a dragging co-axial brake on the drum motor. Marvelous to watch it come up again. Wish the yUK Science Museum would find the courage to try the same on their Ferranti Pegasus. Good luck with the Sprague condensors (capacitors) as those are going to be difficult to replace if they are sickly.

The seals on those bearings will, if done carefully, just pop out. The seals are only designed to keep dust out and are just a push in seal. Careful use of a dentists pick will get them to pop out. I would flush the bearings with cleaner and then refill with grease. The seals can thun be poped back in. Also, just before you shut it off the first time you can see the string on the top fan vent start to blow up. So atleast that fan is working somewhat.

CONGRADULATIONS! A Big first step, glad the drum is spinning and talking! Harry Huskey has got to be smiling also! Wish I still had some of my G15 programs I wrote in the day! Looked for them but no luck! Glad that you are taking slow steps to bring the baby up and working again!

I kept thinking … what if the green button was shorted out? 😳😳 I hope that was checked first.

Oh wow, it's aliiiiiiive! I always am watching out for updates on G15, because man, this is a restoration project for the history books. The excitement you have for this machine is just infectious! I hope the restoration goes smoothly from this moment on and we see this hulking behemoth crunching numbers like it's 1950s again!

that clock signal was a beautiful sine wave

Better watch those selenium rectifiers. Chances are some are bad and the rest may fail after some amount of use. You can replace with silicon diodes if you put a series resistor with them.

Thanks for sharing this. It brings back awesome memories working on similar systems with the military back in the 80s. Yes folks we were not always bleeding edge. Working second shift, TS with old school schematics, drinking coffee and listening to the radio. Some great times for sure.

I want to comment on your channel in general. Seeing the various projects and working through them "with" you is like a refresher course in the old technology. Seeing you interact with those such as Curious Marc and building a comaradare with them, priceless!

👏👏👏🤩🤩🤩👍👍👍⭐️⭐️⭐️🌈🌈🌈 Maybe if you sing japanese children’s song to it the bearings will become less angry ;-)

It's been a long time since "lubricate the memory" has been part of the PM schedule for a computer...

For those Siglent scopes, if you want to see the full sequence, you'll need to zoom out and stop the capture, then you can zoom back in and scroll across until you find the start of the sequence. You can also safely enable the 20Mhz bandwidth limit to help reduce the noise on the trace, and you should also be able to increase the number of points that it captures (although that may decrease the update frequency at the expense of a nicer stopped trace). That said, I'm hugely relieved that you're seeing the expected signals and also filament voltage. This definitely bodes well for the future of this machine. Those definitely look like selenium rectifiers, although I'm not hugely familiar with these early semiconductors. I feel like silicon diodes weren't that common until sometime in the 60s? Maybe be prepared with some extra ventilation just in case. Apparently selenium diodes smell pretty bad when they blow.

What a leap forward on this! Do keep us in the loop on the tape reader and the teletype, man. It's all good.

Great job! Looking forward to the next installment.

Congratulations and Merry Christmas. Amazing that the drum still contains the timing tracks after all these years.

Great stuff Usagi! Thank you for a wonderful Christmas present, and thank you for sharing your journey with all us other nerds and hackers this past year. May you and your family be blessed this Christmas!

An incredible piece of engineering of the day and to restore it into this state is an amazing achievement, well done.

It's so cool to watch and listen to this thing come to life. From a screeching, fighting start to the bearings smoothing out and reading the clocks. Crazy man, love what you are doing. Merry Christmas!

This is incredible! And it's the result of a lot of hard work and brain power on the part of yourself and your partners here. A great Christmas present for all of us, I'd say 🙂

My nerves were jangling when you went for the Big Power, ye gods. I never thought I'd see a G15 ever, aside from history books, and suddenly there's 2 and you have one and it's on the way do being powered up! Awesome. All the best to you and Mrs Usagi from across the little pond.

Wonderful work! Your joy and enthusiasm is infectious! Merry Christmas Eve! I sincerely doubt there are many out there who would put in the level of care and commitment that you put in. It's great to see it!

Congratulations! This was an amazing achievement, and honestly I was amazed that so much of the mechanics and magnetics of this old thing still are apparently working fine. Can't wait to see the further progress.

Really good to hear it's going well, how clearly ecstatic you are with this is great to see, I can't help smiling from your enthusiasm and hope I can get somewhere close to it.

Had an awesome tour at System Source and got to see one of the parts machines for this Friday. Awesome place and awesome tour!

Incredible and good work. Both for those designing this machine in the first place in the days, and to you David for the restauration of it! thank you for sharing this!

Very cool to see this machine working! We had a G-15 in our museum for many years, but we didn't have the knowledge or expertise to get it working. So wonderful to see this machine actually working. Can't wait to see your progress!

Merry Christmas David! Its been fantastic watching you resurrect this machine over the past year. I can't wait to see it fully functional in the New Year

Pretty freaking great. Last night you're singing from the moon, today you're resurrecting this behemoth. Thanks for the work preserving history and thanks for bringing us so much joy.

A super Christmas present indeed! Wishing a very Merry Christmas and Happy New year to you and yours!

I can totally see him hook up a teletypewriter to it, turn it on, install a short paper tape in the reader, hit start, the machine reads the paper tape and the teletype spits out "HELLORLD"

This is such an exciting project! I love seeing the Bendix G15 come to life. It scares me a little bit to see computers that were built during my lifetime being displayed in computer museums. I was 2 years old when this Bendix was built, but I've worked on some of it's descendants including the PDP-8 and PDP-11 both at the DEC factory and in the field.

4:44 thank you and congrats on your safe and reliable electrical installation

I'm really glad you went with solid 2AWG gold and titanium wires with dupont connectors as I would wanted. Better keep the fire extinguisher handy when in use tho

Wow, I'm so glad you had all of this documentation!! It's a treasure trove!

To see that sine wave come up! WOW! So impressed with your work- your excitement is CONTAGIOUS! can't wait to see the next steps! 👍😁

Great video! Your videos encouraged me about a year ago to fire up the PDP-11/23+ and large drives. Had a few bad Sprague caps I had to replace. Hopefully, you will show your process for reformatting the caps in the G-15. Unlike when I powered the PDP-11, I want to test the caps in my Vax 11/30 next before power up which had not been powered up since I purchased it off a BBS swap page in 1994. I am also worried that when I moved, I didn’t lock down the heads. Thanks for the videos.

Thanks for your inspiring work. Being a kind of maker myself, I estimate that you spend a big amount of time creating this high quality content. Cheers from Argentina! 🎉🎉🎉

Amazing, I love seeing stuff from this era working, so thank you for the efforts involved (which must've been no small feat). Please put the old gal to use, these machines were meant to be.

Merry Christmas to you and your family Dave, and all the best to you and yours in 2024, may it be as awesome as the last year has been for your projects! It was such a pleasure to watch the Centurions come back to life and I can't wait to see this near 3/4th of a century old beast do the same! Thank you for sharing your journey with us.

One very large step along the way Congrats David!

Here I thought my boss's 1984 Ikegai AX25 was the loudest machine around! Get some ear protection, better safe. Really cool seeing this fired up, thanks for all the effort. Merry Christmas & here's to a healthy 2024!

So many selenium rectifiers - so many opportunities for really acrid smoke release!

wow! I can understand the tension when you flipped that switch! Amazing! Looking forward to the DC button press!

I think I watch this channel to live vicariously through you, David. Great work 😊

If not for early systems like this one, DEC, IBM and others, our modern smart phones, raspberry pies and so many advanced tech systems would not exist. Thanks for your amazing work to restore one of the MANY shoulders, our modern technology stand on !!

wow man! That's a hair over 5KW to power on. Sir, you always make the coolest and most interesting videos. Definitely one of the top 10 best channels on the entire platform and you should have a million subscribers. (a million and one, including myself). Merry Chrisstmas and all good wishes through 2024!

I love how you sidestepped all the comments about how you hooked up the AC wrong by telling everyone you did it exactly the way people think it should be done. Classic, well played!

I never thought of executing code, was so literal, as in like a machine operation, keep up the good work David !

Feliz Navidad a todos. Y enhorabuena por tu excelente trabajo en el canal. Me encantan tus contenidos. 👌🏼

Merry Christmas! What a gift to watch this today (was traveling this past week). The G-15 series is definitely my favourite one on your channel at the moment, so I was SUPER pumped to hear it start turning on. Wonder how long it's been since anybody heard that on this machine?

It’s Christmas day down here in New Zealand, I’ve got shingles and my Dad has had chemo so I’m staying away from my family and it’s just me & the cat. This video is the best present ever. Can’t wait to see it up and running, good you cut your teeth on the Centurion, this seems like a very well engineered piece if equipment and quite amazing such a complicated machine still functions after all these years. Merry Christmas to you and yours 🎅🎄💝

Awesome. I think I'm going to get to go to System Source when I pick up a car I purchased not far from it. Wish this was there so I could see it. Amazing work. BTW, I'd love a segment on some.of those crazy cars I see in your video like that Honda Beat too!

Merry Christmas and a Happy New Year.. Nice bit of progress. Somebody may have already suggested this but since you have a readable clock and timing signals the first thing I suggest you do is using a decent logic analyser or even a modern scope to capture these signals as a group to serve as a backup incase the timing signal gets damaged. With the clock signal and its backup you should be able to re-write the timing signals onto the drum pretty easily with modern hardware if something happens.

So exciting to see signs of life from the old machine! What a mind-bending thought that the 'clock signal' for the machine comes from a magnetic drum; given that it's using the drum as 'RAM', though, it makes some sense.

I know the feeling of excitement when bringing up a piece of equipment that hasn’t been used well over 40 or 50 years

Wonderful! Very happy to see this working (to the extent it is.) Thanks for your effort on this machine! While I really respect your work here, I don't have much experience with vacuum tubes. Loving to learn from watching you. With mechanical things having bearings, I have worked on them quite a lot. The squeal from ball bearings is almost always due to sliding of the rolling elements due to dried grease. Since you can't get the bearings out of the drum to clean and service them; your idea of using a needle is a good idea. You may want to inject a light oil as opposed to grease, because pretty much any light oil (just a few drops) will help to dilute and soften the grease. Adding grease opens up the worry that it could be incompatible with the existing grease and worsen the problem. I've had good luck adding Lucas Chain lube (aerosol) to sealed bearings to help them out. I would spray it into a syringe and then use the needle to inject it drop at a time. Definitely don't risk spraying the aerosol near the drum and getting oily spots on the coating.

Very cool to see this machine working!

Amazing project and what a milestone. I’ve had to restore a few irreplaceable sealed bearings and have found that with few exceptions you can usually pick the seals of the sides with something similar to dentist picks. The problem is to clean and regressed them you really need to get them out of the assembly (definitely don’t want to contaminate the media!)…. So if disassembly not an option I’m a +1 on a feeding a few drops of gear oil in sideways either through the shields or under a seal lip or with a hypodermic syringe. Though judging by oiler cap at least some are unsealed

This project is going to be awesome to watch.

Woot! That's fantastic! Here's hoping that the rest goes smoothly!

This was amazing to see. I await more updates

> Beware, I live > I hunger

Back in 2001 I ran an old Japanese Punch press machine from the early 60a. The computer absolutely reminds me of that thing. Same color too

Edge of the seat stuff! Brilliant video, thank you!

The bearings should be fairly simple to source. I can make out 105K... on the dust shield, which probably means a metric 25x47x12 (but might not)

Best Christmas present ever. ❗ That's fantastic. Merry Christmas and a Happy New Year.

Had a little chuckle to myself at the power circuit wiring comment but it did get me thinking. There's really not a lot of places with general power circuits, wall socket type things that you plug your TV etc into, that could actually carry this beast. The UK's 32A 230V ring circuit with an appropriately chunky step down transformer would manage it at around 24A on the primary side. The actual normal outlet wouldn't cope with it, 13A is their limit I think.

It's alive, it's alive.... And they said I was mad! Mad do you hear me!

Whew, just took this video off the backlog, haha. Pure awesomeness indeed! Waiting for DC reset after any recombobulation necessary. The chart reminds me of modern OS bootcharts. Some things don't change :).

Wow, what an amazing project! It's baffling to see what engineering marvels were done back then. I had the privilege to see a working Zuse Z23 from 1961(?) executing code in March 2020, in Erlangen, Germany. Also with drum memory, slowly (and noisily) spinning up over a long time... That's the already transitorized variant of the Zuse Z22 (design 1955) that also uses vacuum tubes, like the G15. A Z22 still in working order exists in Karlsruhe, Germany.

That face of pure joy in the thumbnail needs to become an emote on the discord I think

Very cool first start David! Your methodical approach to making sure all elements are actually _ready_ to have power put to them, is vital to getting a working machine in the endgame. I'm amazed that drum has actually retained the clock and timing signals after all these years. All in all, the drum doesn't sound any worse than the old Seagate ST 225 MFM drive in my old IBM AT did when I was running it regularly, and it worked fine! Looks like the caps in that tape drive are a little 'fuzzy'. Probably due for replacement for sure. The electrolytics in the DC bank may or may not come back with reforming.😉 It wouldn't be a crime to replace them with their modern counterparts though, for continued reliability.😊 Looking forward to more on this old tank!😄👍👍

damn, your enthusiasm is contagious! I love it :D

oooooh a new vid on christmas eve, i am glad to see den bendix :) ... i whish you and your family nice holydays!

Merry Christmas from the UK!

Well, THAT'S a heck of a present! Merry Christmas

The fact that anything worked at all is absolutely mind-boggling!

You know you have the good gear when it has oiling points and a sequencer to bring things up in order :) Love the AC adjust knob too. Computers now are so boring!

I have no idea what is going on, these computers are way too old and analogue for me to really understand, but your enthusiasm alone deserves a like! :)

Not gonna lie, those are some beautiful looking clock tracks on the scope.

Woohoo! Congratulations!

That thing spinning up sounds *very* similar to what our old CDC Phoenix on the Wang 2200 MVP used to sound like. Good times. 🥳

as a guy who has worked on vacuum tube stuff for 40+ years, I admire your moxie for having your face fully exposed to the belly of the beast.......I would have opted for a face shield....

Merry Christmas!

Happy, to see the G15 coming back to life. 🎄🤠

my first job at Control Data (1967) was in the systems refurbishment group (G15's, G20's, 160''s 160A's 8090's 1604's etc). I'd like to tell you that I remember everything about a G15 but I don't, wait I do remember 1 thing... if it's not working, open the doors, turn off the light and look for the blue tube and replace it. in 1968 the US government 31 G15 under contract.