Prototype (John1)

Provenance:  This was the first operational Kenbak-1  that John Blankenbaker assembled in late spring 1971, and it was only after he got this working that he sought investors in Kenbak Corporation.  Blankenbaker never sold this computer, and kept it in his home, letting grandchildren play with it.  He finally decided to sell it in 2015, and found it was not working.  He had to replace one of the shift register memory chips.  It sold via Bonham's Auctions on September 15, 2015, for $31,250 to a to a retailer of scientific and technical instruments (Jeremy Norman and Company, Novato, CA) who listed it for sale in their "Catalogue 54" for $65,000.  Achim Baqué of Germany few to California to meet him, and eventually bought it from him for an $41,250, who is the current owner, and maintains a web page about this machine, and his acquisition.

This used the earliest "Rev___" circuit board (no letter after the revision label.)   He did not construct a breadboard of the circuitry - he went straight from the paper design to this printed circuit board (PCB) so it wasn't surprising this didn't work at first try.  This required a lot of modifications and debugging, with many cut connections, and many jumpers to get the computer to work.  This was different in several ways from the later computers:  

1. The power supply board generated +5 volts, -5 volts, and - 12 volts to power the logic board (in later computers the power supply only supplied +5 volts and -12 volts, and then a resistor/zener diode circuit on the logic board generated the -5 volts for the shift-register memory.)  

2. The front panel was simpler and lacked the "lock" switch.  

3. The "store" button was a red "ENTER" button (unlabeled black on later machines).  

4. Many jumpers, and trace cuts were needed on the circuit board.

5. An added transistor, capacitor, and two diodes were installed above the PC board to modify the circuit to get it working.

6. This uses one intel 1404a, and one 1404 (without the "a"-suffix) likely due to the pre-auction repair.

We thank to the current owner, Achim Baqué of Western Germany, for permission to use some of his photos for this gallery.  Visit his web site at thefirstpc.com for much more information.

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