My intuition is they were drafted by hand and reduced repographically based on the age and simplicity…which I mention because a pencil and a scanner are still an option today.

My father wouldn't buy anything he didn't think could be reasonably repaired. Hell--it was a selling point most people took for granted.

From tv sets to most calculators, and even early computers, most had schematics available from the company, and the boards were laid out with repair in mind.

My old HP 454a Oscilloscope was designed to be repaired.

I look at these old circuits and they are art.

I once heard an old Electrician say, "The art of our trade died when we stopped sweating wires."