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Radio Electronics, July 1974 - Mark-8 Issue

Manufacturer Radio Electronics/Jonathan Titus
Model Mark-8
Date Announced July 1974
Date Canceled January 1975
Number Produced Several hundred kits
Country of Origin USA
Price $50 for the boards
Current Value Thousands
Processor Intel 8008
Speed .5 Mhz
RAM 256 bytes to 16K
ROM None
Storage None (can be hooked to a teletype for paper tape or to a cassette with mods)
Expansion Additional cards can be added to the "bus" if needed, but you'll have to build them yourself.
Bus Proprietary - wired from card to card.
Video None
OS Options None
Notes The Mark-8 was introduced right at the forefront of the computer revolution. The kit was created by Jonathan Titus at the request of Radio Electronics magazine. This sparked Popular Electronics, a competing publication, to sponsor the MITS Altair 8800, a machine which ultimately jump-started the entire concept of Personal Computers.
Related Items in Collection MITS Altair 8800, Kenbak-1 and a complete board set for the Mark-8a, a slightly upgraded version of the Mark-8 with edge connectors for a backplane. Also piles of original documentation, the Jan '74 issue of Radio Electronics, etc.
Related Items Wanted Software, additional documentation (especially Mark-8 Newsletters)

I am still in the process of "finishing" this Mark-8, some 32 years after it was last worked on.

The machine came to me in assembled condition with almost all of the components on the boards and with the boards tested by the original owner.

The following series of images depict the boards as they arrived.

The Mark-8 Display card

The Mark-8 Display card is the "front panel" of the machine.

The Mark-8 Input Multiplexer Board

The Mark-8 Input Multiplexer Board.

The Mark-8 Address Latch Board

The Mark-8 Address Latch Board.

The Mark-8 Output Board

The Mark-8 Output Board.

The Mark-8 Processor Card

The Mark-8 Processor Card. The CPU is not yet installed.

The Mark-8 1K Memory Card

The Mark-8 1K Memory Card.

Since the Mark-8 arrival I've been working, intermittently, to get the system assembled and functioning.

One of the first tasks was to get LEDs set up for the display board. Since posts were in place for these I attached Berg connectors to the legs of appropriate LEDs for use with the display board.

LEDs with Berg Connectors for display board

Here is a small pile of the LEDs with their connectors attached. I made many more.

The next step was to attach connectors to the board edges. The alternative would be to use individual wires or ribbon cable for the board interconnects.

Since the Molex connector pins were far too large for the holes in the original Mark-8 boards I decided to use small wire hooks to connect between the boards and the connectors. If I had it to do over again (and I probably will) I would either crimp or file down the individual pins on the Molex connectors to get them to fit properly.

The images below are the cards with the connectors attached:

The Mark-8 Display card

The Mark-8 Display card with connectors.

The Mark-8 Input Multiplexer Board

The Mark-8 Input Multiplexer Board with connectors.

The Mark-8 Address Latch Board

The Mark-8 Address Latch Board with connectors.

The Mark-8 Output Board

The Mark-8 Output Board with connectors.

The Mark-8 Processor Card

The Mark-8 Processor Card with connectors. The CPU socket is installed but the 8008 is not.

The Mark-8 1K Memory Card

The Mark-8 1K Memory Card with connectors.

Once the Molex connectors were installed all that was needed was a backplane with the male Molex pins. My first attempt at this was workable, but I ended up finding Mark Epp on the web and he was gracious enough to send me a hand-made Mark-8 backplane board.

Top of Mark-8 backplane board

The top of the card, with the Male Molex connectors.

Bottom of Mark-8 backplane board

The bottom of the card with lots of solder!

And yes, the card really is bowed as seen in the images. It will be screwed down to a base when all is said and done.

During the construction steps above I was lucky enough to find a stash of power supplies at my local electronics surplus store. These are standard +5, +/1 12V units but there is an internal adjustment for that voltage. As such I was able to tweak one to 9 volts and use a "stock" one for the 5 volt lines required by the Mark-8.

Power Supply to be used with the Mark-8

It's a switching supply which isn't quite appropriate for the system, but I may look for an appropriate linear supply when I'm done.

At this point remaining tasks include adding the Molex connectors for the board interconnects, building the interconnect cables, building a switch bank and then putting everything together.

Once that's all done I can build a case!

This will be a working Mark-8 before long.

The Mark-8 and almost all of the related materials in my collection were generously donated by Jim Voigt.

(Submitted July 5, 2008 20:09:09 by Bob Bell)

Just FYI: I built a Mark-8 replica a few years back on a dare from one of my geek buddies. The story is currently posted on my (mostly outdated) web site: I, too, used the Molex connectors and a backplane that I designed. Maybe there's something in my article that could help you get your's finished. Please let me know, because I'd like to know that there's at least one other working Mark-8 in the world. Thanks.

(Submitted December 30, 2007 07:10:44 by douglas sasse)

had two mark-8 and sold them for $100. total (Had new cpu and no time on them)at minnesota state fairground 'ham' fest. got my altair 8800 just befor I sold them.

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