Soemtron ETR220 - Apollo Era Desktop Calculator... from the GDR!

This has been a major restoration project in my lab for the last year - and now that I got the whole "cage" a.k.a. arithmetic logic unit, I could finally get the thing working. I learned a lot of stuff on diode & transistor logic, ferrite core memory, digital electronics in general... It's technically made in the 1960s/70s (1966-1977), so Apollo time... all this while my side of the world ran on discrete germanium transistors and ferrite core memories. Visit the excellent https://soemtron.org/ for tons of schematics and other info! Mike Hatch is a brilliant guy to have gathered and shared all the knowledge he could find in Sömmerda. 0:00 Intro 1:15 Operating the Soemtron... and Story Time! 11:40 What's Inside 13:55 The Arithmetic Logic Unit (ALU) 14:15 Ah, The Memories! 16:10 Ferrite Core Memory Addressing Control Board 19:30 My Soemtron Repair Story 23:30 Voltage Levels and Diode/Transistor Logic Explained 23:50 Flip Flop and Differentiating Circuit Explained 28:35 Ferrite Core