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Homebrew 6502 c1977

I

ic2024

Member
Joined
Aug 26, 2024
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15
Hi all - this is my first post. I'm now retired and having a clear-out.
My first ever home computer was one I designed and built myself as a homebrew project.
It's not from any kit, magazine or trying to replicate anything else at the time, so fairly unique.
I learned a lot from the project. As it did not have any persistent storage, small programs
had to be entered in hex when powered up.

  • Hand designed and built custom computer, hand-soldered on breadboards
  • Unique Front-Panel display for address and data bus, based on recycled
    1960s computer front panel using miniature low-voltage triode Vacuum Fluorescent Display (VFD) tubes/valves.
    [ from PDP-1 era prototype at MIT Lincoln Labs ]
  • Multi-card with back plane (hand wired, not S-100)
  • CPU: 6502, 1MHz, 8-bit
  • RAM: 4k DRAM
  • TV Typewriter Card by Don Lancaster (from PCB kit) added for B&W text display
  • Custom Bit-map Graphics Card with experimental xor encoding mode
  • Custom linear power supply, classic design 110v 60Hz input.
  • Case is a recycled Tektronix 19-inch rack case with hinged access panel
  • Custom keyboard, 2-key rollover logic
  • Experimental storage to reel-to-reel tape (unreliable)

I'm planning to unpack it out of storage soon and take photos. I've no idea if it powers up after all this time (unlikely).
It's also unlikely I can locate the (hand-drawn) schematics.
My question for the forum is does this kind of thing hold interest to anyone these days?
My default plan is to dump it at the local recycling center after taking pictures for my own amusement.
 
Welcome to the forum. I would like to see some pics of your 6502 home brew - please do post them and the details of the story....love that stuff!
 
ic2024 said:
My default plan is to dump it at the local recycling center after taking pictures for my own amusement.
Click to expand...

I’m sure if you were to post a ballpark location someone would be happy to haul it home for you. (I mean, I would be happy to poke at trying to resurrect it in some form if it were within a 50 mile radius…)
 
Thanks guys for the positive comments!

A1: I plan to take photos around the end of September - patience please.
A2: It's in the greater Portland Oregon area.

More background:
I was doing dedicated logic TTL earlier, and wanted a microprocessor system but could not afford one. I saw an Apple 1 kit in a ByteShop and kick myself for not getting it now!
Much of this project was scavenged components, certainly the psu transformer, caps, heat sinks, etc.
I visited the Tektronix "country store" open to hobbyists at the weekend to get other parts such as the aluminum chassis.
Normally others would have built this with wire-wrap or design a PCB. I opted for hand soldering enamel coated wires, scraping back the enable with the iron, onto breadboards.
I fear this would be a nightmare for anyone trying to maintain it.

Meanwhile:
I was part of a team restoring a vintage 1962 computer near that time - a large ~6x 19in rack beast filling a room. It was a one-off experimental system used for radar/scientific processing called "Casino". It came from MIT Lincoln Labs in bits, all the wire bundles between racks had been disconnected. Our team (of three) was re-assembling and getting it to work again. Compared to today it had some unusual features:

- Germanium transistors (not silicon!) very temperature and voltage sensitive
- Negative voltage (not +5v) with variacs to tweek the germanium
- one PCB card would have a single flip-flop circuit - shows integration level at that time
- "ones-compliment" arithmetic (before the industry adopted 2s compliment)
- twisted pair pulse interconnections between modules
- rotary octal dials (the industry moved on to hex)
- register display made from miniature low-voltage triode Vacuum Fluorescent Display (VFD) tubes/valves.
- core memory
- several large 1" tape drives with noisy vacuum tape transport, used for radar data
- large round radar-type vector CRT display with optical light pen

The Front Panel:
After the project ended and the beast was broken up, I took a part of the front panel display to use on my 6502 homebrew project.
I mounted the VFDs behind smoked plexiglass. Fortuitously the triode gate switching voltage matched TTL output!
 
I enjoyed the story, a true home brew; use what you have and what you can get. It might be a nightmare to "maintain", but there is a lot of history there.
ic2024 said:
TV Typewriter Card by Don Lancaster (from PCB kit) added for B&W text display
Click to expand...
That in itself has historical significance!

ic2024 said:
My default plan is to dump it at the local recycling center after taking pictures for my own amusement.
Click to expand...

By now, I hope you agree that this should not go there.
 
Last edited:
Thanks, let's see if anyone from PDX area chimes in... I've also have things like a homebrew EPROM burner, etc.
 
Rats, Portland. That's about six hundred miles too far. I'm guessing shipping the mess would be a bit steep...

I'm sure there's someone close enough to grab it, though.
 
I would certainly be interested in a description and photographs of the front panel that you used for your creation...

Dave
 
The linear power supply has a large metal can capacitor. What's the best way to tell if it's safe to power up after 50 years?
 
I have had no issues with power supplies that looked awful and ones that liked fine did POOF. My advice: power the PS up outside the house. If it does POOF, at least the holy smoke stays outside.

Once powered up, measure the voltages. If OK, power it off, connect the computer and power it on again.

Success!
 
If it has a linear power supply (as you state), I would take a few precautions first rather than 'hitting it' with the full mains supply in one go.

I assume you don't have a Variac?

If not, a mains incandescent bulb (say 100W) in series with the power supply unit to soak it first would be a good first start.

After that length of time you may need to reform the capacitors, and this would be a good way of doing it.

Yes, always power things up outside first!

Dave
 
That's great advice, however in this case I will be very short of time, and only have access to a simple voltmeter and screwdriver (no variac or soldering iron). I'll have to opt for the POOF test!
 
[ Aside - in my youth I blew up some selenium rectifier stacks - colourful fireworks! Not recommended, don't try this at home! ]
 
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