[magicalhippo]

Since the transistors are used as switches, one can use electromechanical one, aka relays.

There's a nice project page of one here[1], including an in-depth video about it here[2]. There's a collection of other relay computers here[3].

[1]: http://web.cecs.pdx.edu/~harry/Relay/

[2]: https://www.youtube.com/watch?v=tsp2JntuZ3c

[3]: https://github.com/Dovgalyuk/Relay/wiki