Need warnings/ advice/ general info on converting this into a CRT video display for a modern computer.
Posted by Ravens_Quote@reddit | vintagecomputing | View on Reddit | 20 comments
[removed]
probably_platypus@reddit
I'm skipping past all the warnings. You've got that. Still, the consensus of wisdom shared here represents something. Adding my experience to the naysayers:
It's a monochrome CRT, so no shadow mask = no "native resolution." But, you'll be hard limited in how tightly the electron gun can focus the beam (spot size). The spot is also prob an oval, not a dot. This is gun physics, not something you can touch up in software.
For a common 12-inch tube, a 0.3mm spot is typical for 80-column text, but modern resolutions require spots closer to 0.17mm. The image will dim significantly as you tighten the focus.
Vintage green and amber phosphors have high persistence, causing moving objects to smear.
Also, with no shadow mask, light halates within the thick glass faceplate, softening contrast of high-density pixels.
Cool thought, but I'm confident I'd be disappointed in the result. This juice isn't worth the squeeze.
I'm with others here: a totally vintage 80x25 terminal would be War Games cool.
WANT TO PLAY A GAME?
Current-Bowl-143@reddit
It’s: SHALL WE PLAY A GAME?
Ravens_Quote@reddit (OP)
Valid points all, but I'd argue that for a personal project it's still worth the effort regardless, even if I need the next couple years to build the experience I need to get it done safely.
Imagining a near-worst case scenario upon project completion: I boot up 3D Pinball- Space Cadet, can't ever tell where the blasted ball is. I try Stardew Valley, can't tell a house from a hole in the ground. I now have a black and white "video" display too blurry to handle the mouse moving too fast and pretty much only good for text documents.
In such a scenario, I still have have a screen that can display spreadsheets, modern web pages, and formatted text at the baud rate of "It's there now". Furthermore, with the right circuitry, I can rig it so most factors that affect the display become controllable via software. What if I want the beam go down to up & left to right, just for kicks? What about spiraling out from the center? Ah shit, I let family into the shop and somebody busted the oscilloscope... hey, I got an idea! Hell, so long as it doesn't pop anything you could code something to widen and narrow the beam according to what part of the screen it's aimed at (in theory), or do any number of other random science expirements just to see what these things can really do.
Even if it turns out that changing a single thing regarding the motion, width, or strength of the beam just isn't possible without magic smoke coming out, and it really is only good for mostly static images and text, I no longer just have a terminal- I have one-of-a-kind, functional second monitor and keyboard, the modification of which having taught me most of everything I salivated at the thought of doing back when I was a kid looking through my mom's practically ancient World Book collection.
Ffs, its an ELECTRON BEAM GUN, and I'll get to say that I custom made the controller behind it! That's like saying "Ah yeah the only parts of this friggin lightsaber I didn't build are this badass vintage chassis nobody makes anymore and the kyber crystal it came with"! How could I not?!
probably_platypus@reddit
I say go for it.
I'm all for a potentially crappy outcome in exchange for a huge dose of experience.
Besides, it'll definitely run Doom!
Far_Relationship_742@reddit
Destroying an artifact is the main reason not to do it.
Apprehensive-Issue78@reddit
sorry I get all emotional about this post... its a beauty
GlowingEagle@reddit
We'll see if I can reply to a post in limbo.
Note that the CRT is basically a one color (green?) TV tube, likely to have lethal voltages! Also, tube holds a vacuum, so it implodes when broken. Think glass hand grenade.
If you want to make that conversion, you have some major problems. Functionally, it is like a VT100. The (sort of) easy way to connect that to a PC is to use a USB to serial converter. Take a look at this post: https://www.reddit.com/r/vintagecomputing/comments/11d52zn/help_connecting_dec_vt100_compatible_dumb/
The USB serial adapter may use either 3.3 or 5 volts for signal. I'm not sure what voltage signals the Hazeltine 4DTD155394 rs232 port sends. Could be as high as 25 volts, which could fry the adapter.
As for handling a modern video signal, not gonna happen.
Ravens_Quote@reddit (OP)
Reply received! Yay!
As for handling a modern video signal: Mind you I'm talking about outright replacing the existing hardware (outside the bare minimum for the CRT itself to project an image) with an entirely modern board. No need for an adapter when I can wire an HDMI port to an arduino, hook that up to the emitter and write some firmware so it knows how to translate a color image to black & white. That said, of course, one does not simply "hook up" a tiny lil' PCB to an electron beam emitter that only turns on for big boy wattage, which is where my lack of pre-modern tech knowledge comes in.
Basically, I need to know exactly which components determine the strength of the beam, and which ones determine which way it bends/ how much. Once I've got that and know how much juice to send down what line for what effect, it's all firmware from there... in theory.
It's tech heresy of nearly the highest order and by all means desecration of a rare and sacred relic, but I can always send the board to whoever needs the chips to repair their own vintage machine, and this does still save the ol' girl from the landfill.
... and to answer your question: I don't sleep at night, I don't face myself in the mirror, and I don't know how I live with myself either. Love garlic powder though, so at least I'm not a vampire.
GlowingEagle@reddit
OK, manuals exist: https://vt100.net/hazeltine/h1420-rm.pdf
Looks like 7x10 matrix for each character, 24 lines, so still low resolution.
Still looking for decent circuit diagram...
Ravens_Quote@reddit (OP)
How the hell y'all even find this stuff I got no idea lol. Google damn near claims this whole terminal don't exist outside some dumbass making a reddit post about it in 2026- some edgelord soundin' name, like they wanted to make an Edgar Poe reference but "Nevermore" was taken when they made their high school G+ account.
Anywho, as to budget on money & time: There's no hurry on any of this. It's a hobbyist project so I got no corpo deadline to meet, and with my lack of experience it'd be suicide to touch anything in that case until I've actually got some breadboarding under my belt. This post is basically me popping a flare on account of having no friggin idea what info I even need, nevermind where or how to find it.
Thanks btw, even just the PDF is a shitload more than I would've found on my own.
GlowingEagle@reddit
The essential pdf to find is the maintenance manual: Hazeltine number HI-1082. This does not seem to be anywhere.
To get an idea of the kind of circuitry that was used at the time, check the schematic diagrams in this pdf for the model 1500: https://www.vintagecomputer.net/hazeltine/1500/hazeltine1500_maintenance.pdf
When you understand that model design, you would be ready to figure out and draw the circuit diagram for the model you have.
GlowingEagle@reddit
Possibly, you are a mutant vampire :)
Screen resolution is limited. May have 80 characters per line, 30 lines, 6x10 character dot matrix, so that the screen dot resolution is 480x300 "pixels". I expect the beam that lights the florescent coating inside the tube, is swept quickly left and right, and more slowly up and down, like an old TV scan pattern. Blanking the beam on/off produces the pattern of text on the screen. The refresh rate is probably similar, like 30 frames per second (guessing).
The CRT is fed several signals: High Voltage for the beam, blanking (or intensity) modulation, vertical beam displacement signal and horizontal beam displacement signal. The last two probably go to magnetic coils on the neck of the tube. I think you want to keep that circuitry, but find out where you can feed lower voltage signals into the amplifier that drives blanking.
Manuals and circuit diagrams are scarce, so you need to figure out what you have. It the unit working now? Do you have a voltmeter and oscilloscope and experience tracing circuits? What is your budget (time and money)?
GGigabiteM@reddit
This project is like a novice skier looking at the bunny slope and then doing an about face and running full force into the double black diamond slope.
Not only is this complex electronics, this is complex high voltage analog electronics.
There is not going to be any off the shelf solution that you can buy that will turnkey get you a monitor you can plug an HDMI cable into. The closest you'll get is one of those generic AliExpress driver boards that are designed to replace clapped out/damaged analog boards on TVs, like this: https://www.aliexpress.us/item/3256806024115198.html
These have no instructions and require you to know exactly what you're doing These are also designed for color tubes, so heavy modification will be required to work on a monochrome tube. There may be some of those boards that are made for monochrome tubes, you'll have to look around.
But don't expect miracles. Monochrome tubes don't have shadow masks or aperture grilles, so they don't have a hard upper limit on resolution, besides being bandwidth limited. You can probably get most resolutions that other monitors of the time could get with similar tubes. 720x480 and lower and interlaced modes with a generic driver board.
You should do extensive research before attempting this. There be dragons.
Ravens_Quote@reddit (OP)
Exactly the reasons I'm here lol. Thankfully I'm smart enough to have already known going in that I've got no business popping the hood on this thing for a good long while, I just need pointers on where to start researching aside from the obvious "learn more about vintage electronics". Can't believe someone [actually found the friggin manual](https://www.reddit.com/r/vintagecomputing/comments/1t2ygvp/comment/ojsdj9t/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button], so that'll be a fine read and a pretty penny to print.
All that said, this post is likely to go without a follow up for a good while. Truth be told, while I do have the luxury of time, money's not quite so abundant. I can't afford a bunch of equipment I'd need to get practicing, so for now it's just a matter of reading all I can while I bide my time.
Alarming_Cap4777@reddit
The issue you gave here is that it cannot process a Luma signal. You would need to build a circuit the breaks the Luma signal down to the H/V Sync and lines. Sort of like a composite to VGA converter.
hamburgler26@reddit
The absolute first thing in the manual for this other than the title and company name is a giant warning about how dangerous working with this thing can be, and you're saying you have no experience even with soldering modern equipment.
Find somebody who can help you in person with real experience. Please don't just crack this thing open and start tinkering based on Reddit advice.
Ravens_Quote@reddit (OP)
Don't worry, I'm not THAT stupid. That said, kind of a major problem:
I'm the only computer nut in my family AND my non-work friend group, everyone I work with is my age with NO interest (nevermind experience) in hardware older than they are, and if you've checked the obituaries you might have noticed a growing number of y'all that were old enough to code in the 70's are pushin' up daisies now.
I got me. I got common sense enough not to get myself killed, but beyond that I got nobody to talk to IRL about any of this that would even know "floppy disk" used to mean it was floppy, nor contacts that know anybody who would (save one guy, but by his own admission he only ever did software, which doesn't help here).
Now, disclaimer, I come off a lot harsher than I mean- including all that text above. Long story but TLDR is I've lead a life where you're either blunt or you're misinterpreted, and even that ain't always enough. You're 100% right on not cracking the case open rn, and were this a different decade or were I surrounded by people who had experience with this tech, I'd even agree that I shouldn't do this alone. Alas, it just ain't the situation I'm in.
If it makes ya feel better though, there ain't any rush on this project. I've got no deadline and I'm in no hurry to fry, so there'll be plenty of unrelated breadboarding projects completed before I even bother with this beast. That said, I still need a starting point for the shitload of research I gotta do, and this post is to help me get in that direction.
Genuine thanks for the concern, and it's always good to have folks like you around.
compu85@reddit
Why gut the terminal? Get it working properly then you can connect over a serial port to Linux / macOS and have a console.
Ravens_Quote@reddit (OP)
Valid question! And the answer... has a few angles to it.
First off, practically speaking: I have neither hardware which requires a vintage terminal, space to store such, nor reason to use that as much space as this terminal uses to perform only the functions it does. Sure, I could have a console for a Linux operating system, but I could also use an LCD screen to do everything this can and more.
This of course begs the real question: "Why bother keeping a terminal for which you have no practical use, especially when others on this subreddit would glady take it off your hands?"
Answer: I'm not keeping the terminal part. I'm keeping the CRT, the case, and the keyboard. If you want the chips, board, or port off this thing, it'll be yours once I know I can safely get it out (fair warning: That'll be a while).
I want to experience the oddity that is playing a modern game on a screen never meant to go with it. I love the aesthetic and durability of the case. The keyboard layout is a fascination all its own, nevermind how solid they keys are, and I can't wait to start integrating functionality for the clear, clear field, and break keys into a modern OS.
To a collector? Yeah, this is pretty much blasphemy. To me? This is getting to experience things NOBODY gets to experience. Sure, you can probably display E1M1 on your own terminal using ASCII art and the tower it was originally meant to be plugged into, but have you considered how fascinating it'd be to see somebody at what appears to be a standard terminal, get a good look at the screen, and realize they're playing Crisis? Cuz owning that machine, getting to pick a game you've never seen in black and white before and playing it a way it was never meant to be played on a whim... you can only buy the hardware for it. The experience is priceless.
nmrk@reddit
Hazeltine terminals do not have video input. They have ASCII input over a serial port.