as far as I know this is the oldest running digital computer in North America it's a Bendix g15 a full-fledged vacuum tube computer from 1956 and actually I'm pretty sure it's the only running Bendix g15 in the entire world which is pretty wild in and of itself but when you start considering the history of this machine it gets even crazier because this machine was designed by Harry husky who worked with Allen Turing and Tomy flowers and not only that a lot of the design characteristics that Allan Turing built into the pilot Ace found their way into this machine this is kind of like the spiritual successor to the pilot Ace so this is not only the oldest running digital computer in North America it has an extremely strong link to the birth of computing everything that we can do today the camera that is filming me sitting here talking can all Trace its lineage back to this machine and it can its lineage back to Alan Turing and Tommy flowers that's just absolutely mindblowing to me so how on Earth did such an important machine find its way into this room well this machine is on loan from Bob over at system Source Museum and if you haven't heard of system Source Museum go check them out immediately I say this every episode and I mean it from the bottom of my heart heart system Source museum is one of my favorite places on the planet and Bob is just an excellent person he gets these machines like we get these machines and he wants to see them up and running because a running machine can teach us so much more and so that's why he sent this g15 all the way down to here so we could get it up and running and in the previous episode we did just that we loaded up the diaper which is a hilarious name for a program it stands for Diagnostic program for easy repair uh but it it's essentially a program that has a bunch of Diagnostics on it we loaded it up ran it to completion every time it passed a test it would ring the bell and when it got to the end of the tape it rang the bell like six times in Rapid succession it was absolutely awesome so the next step is to load up diaper Real 2 which has much more indepth and complex tests on it like it's going to test multiplication and division and some other really tricky things that the Bendix is capable of and I'm actually expecting that reel to fail because we have some uh modifications going on on the inside with some wires soldered into strange places and one of those wires I know for a fact is broken and so I'm expecting us to butt our heads up against that but before we can even get that far we have one huge massive problem that's preventing us from just throwing in intercom or alal and just writing new software for this thing and that is that well the machine needs input and output and the input and output primarily is done through the typewriter and this typewriter is a pretty interesting typewriter because it has a 28 in platin it is massive and ridiculous and I love it and it seems to be receiving output from the g15 just fine I mean aside from the fact that we need a new ribbon and a little bit of adjustment going on so the Hammers hit the hit the platin a little harder but the input into the g15 from this typewriter is not quite right it does work somewhat I can press s and I can press carriage return and those send signals to the g15 and g15 knows how to go on from there but the numeric portion of it just doesn't work like I can't hit any of the letters numbers 0 to 9 or letters u to Z and some of the other letters on the keyboard should be doing stuff like I should be able to hit P for uh photot tape read or stuff like that and that just doesn't seem to be working right and I think it's because somebody modified this typewriter to essentially turn it into a printer but if you just wanted a printer why remove the output functionality of it like it it doesn't make any sense to me so what I'm going to do today is I'm going to take pictures of the PCB that's inside of the typewriter make sure that we have good documentation of it and then I'm going to try and Dem modify it we're going to try and get it back to original specification so that way we can plug this into the g15 and now we can start using it as it was originally intended but that's going to be pretty difficult because there's a lot of wires and a lot of soldering that needs doing so let's get this onto the bench and get [Music] started now that we've got this Behemoth ~ Introduction Segment Removed ~ of a typewriter up on the bench Let's uh go ahead and see if we can get it apart and in order to do that I need to tilt it up onto its backside then on the bottom the four rubber feet are actually screws that uh thread into studs and hold the entire bottom piece on so we'll just unscrew those and the entire bottom piece kind of rotates it down now in order to get the bottom piece completely free we need to undo the two plugs that plug into the side here they're not locked in with screws or anything so you can just kind of slide them out and unplug them and with them unplugged we get the bottom half completely free this thing is wild looking inside and this is not the first time that been in this thing we did have it apart uh earlier so we can get to work on some of the mechanical aspects of it clean it up and try to get it typing well and it seems to be working mostly Okay it definitely needs a new ribbon got one of those on order don't worry we're going to try and get that in there this episode depending on how shipping in December goes who knows it could be lost in the mail um but today is not a focus on the mechanical aspect of it we really want to get the electrical aspect of it going and somebody's been in here and modified it I can see that there's some cut wires up here as as well as down here and a bunch of stuff has been completely resolder now some of these cut wires might not have been modifications they might have been that way from the factory just extra wires run up there for potentially different versions of the typewriter I don't really know about that but down here where all the wires are slded together in kind of one big mess that's definitely a modification and then there are jumpers that jumper over specific diodes and I think we can maybe remove those jumpers and get this thing back to some semblance of Factory uh and I'm not going to just like desolder things and just kind of take a guess at where they go we do actually have the schematic from the uh theory of operation manual so we can actually see what the diode Matrix should look like and we can see what keys should connect to what so I can actually start beeping out connectors on the PIN to specific wires and then figure out where that fits on the diode Matrix here and make sure that the diode Matrix is correct as well as all of the diodes are good cuz we may have a bad geranium in the middle of here somewhere as well let's start by repopulating the resistors that had been removed I previously resered a few of these but it looks like in all six different resistors have been either removed completely or had one of their legs lifted they're all just simple quarter watt carbon composition resistors and they're all acting as pull Downs to the ne2 volt rail so I can replace them with these modern resistors no problem after the resistors let's get this insane mod wire out of here I previously put fresh tape on it to keep it from shorting out to anything else in here but other than that this is how it was when I got the typewriter about 20 wires have all been tied together and I know that's not right I'm going to add a little fresh solder to break the connections loose then I'll separate each individual wire it's tedious and finicky because nothing is stable and the solder is old but eventually I got everything free and spread part then I just need to figure out where each wire goes thankfully the manual is pretty helpful here for example we can see on the schematic that the letter Z goes into plug number one on pin y That's Right Z is y confused yet but but that means I can put one Probe on pin y of the plug number one connector and check to see which wire has continuity once I find it I can solder it back in place thankfully the PCB is marked with the pin names so just have to find the letter Z and solder it there it's a little hard to see but from left to right in this shot you can find Tab S and zero and the rest of them all look like this and now that we've done it once we have to do it 20 more times find the letter or number to work on look up what pin on plug number one it is check for continuity from that PIN to a specific wire strip the wire add fresh solder find the appropriately marked place for it on the PCB solder it down and repeat for the next one I got my I work out in for sure is I was constantly going from one side of the table to the other but after surprisingly not that long check it out the typewriter is looking much tidier inside the final thing that I did was remove a few jumpers that were shorting across a few of the diodes and with it all back to factory spec now I think this thing will work beautifully however speaking of the diodes I do want to try and test them if possible unfortunately because they're all arranged into a big matrix it's impossible to isolate a single diode for testing you can see that we get a decent reading in the Ford Direction but the diode Matrix just blasts our reverse Direction reading we'll just have to do trial by fire for these diodes but now that the typewriter is back to normal what was modified you can see on this diagram that carriage return space minus Tab 0-9 and U through Z were all disconnected and tied together then bit level five was disconnected and tied into that mes that means that if any of those keys are pressed it would send a 1 00 code which would get interpreted as a zero then to confuse matters more they removed r21 R22 r25 r27 r28 and R34 then they jumped across diode 21 and diode 30 and connected the jumped diode 21 directly to bit level one I think we're seeing two different modifications here one superseding the other either way I can't make heads or tails of it but at least we have it archived for future reference now all right typewriters all back together let's just give this thing like a quick sanity check make sure I didn't make anything worse so I've already brought AC up we'll hit the reset button here that'll bring DC up the sequencer should be going through we should see the yep the paper tape reader kicked off it should be reading in uh the number track right now it'll stop then it'll read in the first block of diaper because that's the program that I currently have loaded into it when it finishes reading this it's going to hit a pause and wait for me to hit the go switch on the typewriter when I do that it should uh punch some stuff out on the typewriter and I think that'll be a pretty good indication that we haven't made anything worse so it's currently waiting on me to do that I'll go ahead and flip the G switch Yeah it hit the typewriter it's reading in the next block I I think that's a a pretty good sign it didn't actually type anything out because again bad ribbon and probably totally maladjusted and that's a problem for future David all it would have printed out is just uh the number one like six times so it really we're not missing anything fancy there uh but it it read in the next block I think that means that the system is working let's go ahead and hit s here and yeah it's going to read in the next block it's going to continue on its way and honestly that's actually about as much interaction as the diaper is expecting from us via the typewriter there is a test about Midway through test number seven I think that wants you to to uh punch in a random number and then hit s and we've been able to skirt by that test anyway so uh we really need something more involved to uh properly test the typewriter out on this thing so uh I'm going to punch out a new tape and we're going to try something pretty interesting here time to punch a new tape which means I get to use this awesome faucet punch again I've always been calling it facet but you guys let me know that it's pronounced with a long a anyways I load up the blue paper tape that Lloyd sent me this stuff seem seems to work a little more consistently with the photo tape reader I'll Loop it around the correct tensioners and then around the bottom then slip it into the five level guide and through the punch mechanism and once it's out the top I'll thread it through this tensioner sensor here I have no clue what this is actually for but we might as well use it then it gets a spiral around the back post and looped onto the top reel I'll just uh tape it in give the button a few presses to make sure that we're loaded correctly then hop on the laptop set teraterm for 6008 in1 load the binary file and send it over and way it goes making an absolute racket I love just sitting and watching this thing work watching the tape spool onto the top reel or getting pulled through all the different tensioning wheels and being able to see the actual data stored on the tape as it flies by or most importantly watching this thing create a mountain of Chad confetti I'm still vacuuming this stuff up by the way I desperately need to build a bit bucket for this thing but once I click Send the process takes about 5 minutes and it's purely a hands-off thing I don't need to babysit it or anything it just sits there and creates new data tapes perfectly and of course at the end of it all I do get the satisfaction of vacuuming up all the bits that fell onto the table tape is punched we've got it mounted let's turn the DC on here we're going to hit reset that's kicked off it should start reading in the tape yep there we go so the first block of this is just the number track but the second block is where it gets interesting because this is not a diagnostic tape this is a real deal legitimate program that's going to require input from the typewriter and it's going to give us some interesting output hopefully if I can figure out how to make it work uh I've been kind of struggling with this for a while uh actually I've got a bunch of handwritten notes over over here uh so if I look at my handwritten notes Here we want to do console switch to go and it should start reading in more blocks of data off the tape okay so it's going to do this for a long time it's going to sit here and read blocks off the tape for uh I think like 16 blocks or something so it it's it's going to take it a while um so we'll just sit here and uh twiddle our thumbs until it's done okay all blocks of tape have been read in so we're going to take the compute switch put it back to the center here here uh and then we want to turn the enable switch on and we want to hit the letter P here that should cause it to start reading again that's good so we're going to turn the enable switch back off and it's going to read in one more block of data and it did that so now it's paused and it's waiting for us to go again so we want to do the uh compute switch to go it's going to hit the typewriter and type some stuff out yeah and then it's going to read one more Block in and then I hit the typewriter again okay uh okay now it's paused and my notes are coming to a rapid end here but we're going to we're going to type some stuff in here so we're going to do a 0 0 tab slash and then a 2 V Z Tab S it hits the typewriter it does some stuff then we're going to do a V2 Z Tab S hits the typewriter again does a carriage return uh and now we're in an interesting position where I have no more notes but I've been messing with this if I can get the right incantation going on we should see something on the scope here um so it's I think it's we'll we'll try something here all right I think I figured it out uh it's slash L Tab S uh and that seems to make it do stuff you saw that there was a square wave on there temporarily right now it's doing a whole lot of blinking lights up here and if I'm not mistaken we should get some more square waves showing up here shortly yeah there we go check that out oh that is awesome that is very very very cool uh okay what what is this uh well we're we're we're doing something a little kind of crazy here and uh hopefully the next step of this is going to make it all very very very clear exactly what's going on so I'm going to take the steps towards getting that accomplished and then I'll come back in and explain everything that's going on all right let's pull out a little Proto board here and solder a few 1 megaohm resistors and a header to it uh then I'll slot in a pair of 0.01 microfarad capacitors and tie those into the resistors finally I'll solder in another header and our Proto board is ready for installation I want it permanently mounted to the chassis but kind of out of the way so I'll just slot it onto this long stud here and tighten it down then finally I'll solder some wires is going from two packs on the door to our little Proto board yeah that's right the machine has been working for like a week and I'm already modifying it all right I've got the camera way way back and because I'm going to have to be doing a a bit of running around here and I've been like soldering stuff up I've soldered some stuff to the doors I've been doing all sorts of stuff showing you Scope traces and I haven't really said what exactly it is that I'm doing uh and that's because if if it works I think it's going to be pretty awesome or it'll be hilariously bad I don't know but you can see I've got an additional tape kind of set up here in a little bit of a janky way and that's because I'm I'm out of cartridges I need more of those little cartridges that you put on the front here maybe we can make some of those up someday uh but anyways there should be something pretty special on this tape I mean we've already done a lot of really special stuff We've ran the first Real Deal program that AB indix g15 has run in probably 30 years that's pretty exciting but I hope this is going to work so I'm going to walk over to the typewriter here and I'm going to tap type sl5 tab SLS uh so das5 tab slash S now it's going to start reading I'm going to have to kind of hold it here because again I don't have uh I don't have a cartridge whoa tell hear that it made a noise [Music] can you hear it it's playing music it's terrible music and I don't think it's quite [Applause] right it's supposed to be Christmas music [Music] [Music] now that I've had like a day to catch my breath from the insanity that just went down what exactly happened well we tried to play music on a vacuum tube computer from 1956 granted it didn't sound very Christmassy and it didn't didn't sound very musicy but this machine was outputting square waves that the morance amplifier was picking up and playing as tones over the JBL speakers the concept works but how is that even possible well at system Source Museum they have a ton of paper tapes and magnetic tapes and uh documentation and Lloyd and Rob to Absolute Legends in the g15 community have been making regular trips to systems horse Museum to archive all of that well not the magnetic tapes yet we haven't figured out a good way to Archive those yet but the paper tapes in particular have been archived and backed up and among those paper tapes that they've been archiving they came across a tape labeled music program and a tape labeled Christmas music and that's what we just tried to run we loaded up the music program and then we tried to load the Christmas music data and we got that hilarious concoction now I will say that if you speed up the uh sound that's coming out of it to double speed it sounds a little closer to [Music] music but if you were to record it and play it back at Double speed it would change the pitch which wouldn't sound right so we're fairly certain that the data tape that we have that says Christmas music is not for this version of the music program that we have but how is this music program taking this concoction of vacuum tubes and wires and turning it into sound that's being played on the morans well they had me we found we found some documentation that's the only way we figured this out we found the music program documentation and they outlined how to modify it you uh solder a wire to the read amplifier of line two and the right amplifier of line three you run them through some 1 megga ohm uh resistors into some coupling capacitors and then run that into your amplifier so the sound that you're hearing is coming straight from line two and line three on the drum so how are they making those lines produce sound well we could actually see a bit of that when we punched the paper tape for the music program the music program itself is only like one or two blocks long the rest of the blocks that got loaded in were collect of Zer and ones and depending on how many zeros and how many ones you have you can change the essentially waveform that's on that drum if you have uh 100 zeros and then 100 ones and then 100 zeros and 100 ones around that drum it's spinning at a known speed and then you're reading that data back it's going to look like a square wave and then you can change the number of zeros and number of one to get different square waves that give different tones so they loaded up a bunch of tracks on the drum with different Square that are made up of data zeros and ones and then whenever they want to play a tone they copy the correct note from one of those tracks over to line two or line three and then the amplifier sees that and plays it as audio and we were only able to get this far to get that program to run because of Lloyd's unbelievable work he has a gate accurate cycle accurate emulator that he's been building and using that that we were able to look at a ton of debug information from the g15 and kind of figure out what the program was expecting and that's kind of how we came to the conclusion that the data on the Christmas tape is not for this version of the music program but this music program is not just a playback program when we first started this I typed in a couple of uh letters on the the typewriter here and we saw a waveform on the scope and what I was doing there was actually programming a new song so you can use this software to write new music and Lloyd was incredibly unhappy with the result of the go that we were reading in before and he sat down and figured out how to program a new piece of music in and all I have to do is type-5 tab SLS it's going to start reading in this tape that he punched for me and Silent Night Real Deal Christmas [Music] music oh that's so cool that's awesome I want to thank you all so much for watching and I want to wish you all the best Merry Christmas ever up [Music] [Music] [Music] all e for ~ Outro Segment Removed ~ Back To 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