[dwarman]

We built relay computers in HS in the early 60's. There was this street in London: Lisle St, in the Soho district. One could buy surplus PO 3000 multi-pole relays there real cheap - up to 10 pole IIRC. These were the relay type used on the Post Office Telephone exchanges, pre-electronics (up to #5?). In 66 I also discovered a recently published book by Russian authors: "Introduction to the Theory of Finite Automata" by Trachtenbrot and Kobrinskji https://g.co/kgs/EqZYC2 which taught me the formal of the topic using relay logic. I believe the robustness of Russian space tech was due to use of relays as well as tubes. That book gave me my career, effectively; turned out to be equally appropriate for electronic logic circuitry.