1A1 was an insane bank of relays that covered a 4x8 sheet of plywood for a couple dozen lines.

1A2 used shoebox ksus and 13 slot panels with an interrupter. Much more compact.

Take a look at these sites. Just call me the google maven.

https://209.165.152.119/tel/1a2.html

https://www.ntcp.com/default.html?target=dept_461.html&lang=en-us


THE Bracha, old blond specialist in Rube Goldberg solutions.