SCELBI 8B Progress

September 23rd, 2014

Memory Expansion Board is almost done – I’m short one 7442, which will prevent me from checking out the last slot, but otherwise it’s ready to go. This board went pretty quick, the 67 resistors took as long as anything else on this board.

Memory Expansion Board

Memory Expansion Board

For now, I’m hacking together a wooden chassis with sheet metal front and rear panels. Once I get the aluminum version figured out, It will be easy to move the backplane and front panel switches from this hack job to the final chassis.

Temporary Wood Chassis

Temporary Wood Chassis

As far as the possibility of the short on the 4K SRAM board, though it’s pretty remote, I decided to add some masking tape to the bottom of one end of the fuse holder to eliminate it entirely.

Fuse Holder Masking Tape

Fuse Holder Masking Tape

Given where I’m at at this moment, I expect I’ll be able to power up the 8B with 4K of SRAM within a week.

Nat Wadsworth: How did biology get into the name: SCELBI

September 18th, 2014

I learned this last year and figure I should share it before I forgot or worse.

At VCF southeast in 2013, I briefly met with Nat Wadsworth’s sister in law. She told us how Nat kept birds in his basement and developed the SCELBI on the second floor of his house.,-73.0073396,3a,90y,288h,90t/data=!3m4!1e1!3m2!1sUm1aprSPCyd5yaSyYp0ckw!2e0!6m1!1e1

She told us that Nat was studying bird diseases which accounts for the biology part of the SCELBI name.

8B backplane and 4K SRAM Soldered

September 15th, 2014
8B backplane and 4K sram

8B backplane and 4K sram

I found a small issue in the layout of the 4K SRAM card. The trace leading from the ground past the fuse holders passes too close to the fuse holder for comfort. Since there is no solder mask on these boards, it would be best to mask this trace at this point with tape or something so it can’t inadvertently touch the fuse holder and short +5 to ground. Reviewing my layout, it looks like I missed aligning this trace correctly to the original layout. The layout in this area was obscured by the 10uF capacitor, and I didn’t notice the difference when comparing my layout to the original.

Ground Fuse Holder Issue

Ground Fuse Holder Issue

Next board to solder is the memory expansion board. It it will be fun putting in the 67 resistors that populate that board. Then I’ll have to cobble together a chassis for testing.

Apple 1 Registy updated and new SCELBI registry

September 14th, 2014

I just posted an update to the Apple 1 registry. One system was deleted and one added, so the total count holds at 63. The new one is John Anderson’s, which will be sold at auction, next month. I just was contacted by the owner of what is probably an unlisted system, so the count could grow to 64, very soon. Christopher’s system, which has been shown at K’Fest, VCF midwest and VCF east has been undergoing some restoration, so I added an updated image and additional information.

Note that the success of the Apple 1 registry is largely due to contributions of owners and former owners and other interested parties and I greatly appreciate all new information.

What’s really exiting to me is the new SCELBI registry. If you think Apple 1’s are rare, I could only find information on 13 SCELBIs. I recently received information on what could be a 14th, but it also possibly could be the missing Freeman Museum unit. The images on the SCELBI registry will be a little different than the Apple 1 registry, as the images will emphasize the quirks and differences between the units. Many original SCELBIs don’t exactly look like factory stock systems, so Iit should be a good resource for people building reproductions.

I expect that some of the information may be incorrect. Bear with me as I expect to refine this registry quite a bit in the future.


September 11th, 2014


The SCELBI 8B backplane, SRAM and memory expansion boards just arrived. They may take a couple of weeks or so to check out. If they work, I’ll be able to get floating point SCELBAL up and running on an 8B for the first time in a very long time, and so will you. There is a semi-reproduction that has run SCELBAL, so maybe not the first, but it all depends upon how you classify that system. To start with, I’m building a minimal, barebones, chassis mainly to allow check out of the SRAM and get SCELBAL running.

You will notice that there is a stack of cards involved. The big question is whether I finally screw up a layout and have to ditch one of these batches of cards. To date, I’ve never made a small prototype run of a few boards to check my work. There were prototype’s made of a few of my smaller cards, but they were either made on prototyping boards or etched here at home, where the cost is almost nil, compared to professionally made PCBs. The benefit of this rather risky approach is that I save a great amount of money by not making what would be rather expensive prototypes. This directly translates into a lower cost project for you and me. In addition to the risk of making a complete batch of dud cards, another downside is the great amount of time spent reviewing the layout before I eventually pull the trigger.

at last – PCBs for SRAM only SCELBI 8B are now on order

September 3rd, 2014

Some people have been asking for these for a couple of years – well I hope the wait will be worth it for those people.

I have also started serious work on the PROM card. Turns out that I will probably end up going over and tweaking the entire design that I started with, so it will take a little while. Not as long as doing the 3 other boards, but those that are interested will have to wait a little while longer for the PROM boards.

I’ll have the PCBs in a week or two, but I also need to order a few parts so that I can build them up and do some sanity testing.

New Toy

September 1st, 2014


This is the first piece of gear to be used to expand my vintage computer hobby into a new direction.

Bicycle Wheel Rebuild

August 26th, 2014

It started as an assortment of parts

wheel parts for rebuild

wheel parts for rebuild

  • old Wienmann A129 rim (great touring rim)
  • new DT 14 gauge stainless spokes in two lengths
  • new DT spoke nipples
  • old greythumb nipple lube
  • new old stock malliard heliomatic hub
  • rim tape
  • old skewer
  • park nipple wrench
  • Jobst Bradt’s book: “The Bicycle Wheel”
  • and a few hours later I have a new wheel…

    wheel together and mounted onbike

    wheel together and mounted onbike

    One thing about truing your own wheels, they are going to be as true as the rim allows, if you have the patience to really fine tune them. I don’t have a runout gauge, but I wouldn’t be surprised if the runout measured 1/100″ or so on this newly built wheel.

    Total cost was about $100, but I ended up with a spare used hub in addition to the new old stock hub when I pulled the trigger on an ebay auction a couple of days before the NOS hub came up.

    Now to find a NOS hub for the front of my lightweight training wheel set – the bearings bind on that one unless the hub is put in the fork in a certain orientation.

    Dover Mini-Maker Faire Experience

    August 25th, 2014

    Dover, NH Mini Maker Faire

    Dover, NH Mini Maker Faire

    Just sharing some experience from the Dover Mini Maker Faire which was Saturday. I had Micro – Chess going on the Mimeo and Dave Ahl’s HI-LO in tiny SCELBAL (integer BASIC) on the SCELBI. It was busy almost the whole day, just a few fairly brief periods between visitors. It seemed a bit busier than Saturday at VCF.

    HI-LO was the perfect text game for casual visitors of all ages – simple to teach and quick and easy to play – I was impressed by the number of small kids that immediately proceeded to use a binary search algorythm to find the number.

    A lot of people tried a few moves on chess, but the user interface is so awful on the Apple 1 port of micro-chess – I had to train almost everyone – even though I had instructions posted.

    I met an original Mark-8 owner(still has his system). That guy added a digital group video card to his Mark-8 and made some improvements to it, which were used by later generation Digital Group video cards. Another person who was into SWTPCs in the day. Another person that was once vice president of the Boston Computer Society. And finally, another guy who worked with Draper Labs on the Apollo guidance system computer.

    There was a wide variety of exhibits from art and crafts to a young man who was building a neutron generator. If you have a mini-maker faire in your area, I’d say it would be worthwhile to show off your gear – you might meet some interesting people.

    List of all SCELBI PCBs

    August 20th, 2014

    I plan to reproduce all the SCELBI PCBs. There are 16 types of boards in all. The 1106-1108 8B boards are practically ready to be made. I’ll probably tell the PCB factory to start on them this week. This will mean that in a few weeks I’ll have 10 of the the 16 boards done. The really good news is that most of the remaining cards are only single width, so reproducing them should go much faster than the double width system cards.

    Here is the complete list of the PCBs that SCELBI Computer Consulting made and my reproduction status. The peripheral cards are listed in my most likely order of reproducing them

    Main System Cards
    1100 CPU – 8H/8B
    1101 Data bus buffer – 8H/8B
    1102 Input – 8H/8B
    1103 Backplane – 8H
    1104 Front Panel – 8H/8B
    1105 1K SRAM – 8H

    In progress
    1106 Memory Expansion – 8B
    1107 4K SRAM – 8B
    1108 Backplane – 8B
    1109 PROM – 8B

    Peripheral Cards
    2104 Teletype interface*

    Not started
    2105 Keyboard
    2100 Oscilloscope digital**
    2101 Oscilloscope analog
    2102 Audio Tape output
    2103 Audio Tape read

    * not as high as normal vector boards
    ** double width vector board