I'm not really a R-390/R-390A nut, but I can't help but admire the incredible engineering in these radios. I hadn't heard of them as a kid. I guess this is because they were classified (!) until 1968 (!!). I am told that the Pueblo that is still somewhere in a North Korean harbor has a number of these units aboard.
There is a document floating about the web that is an engineering report on the construction of the R-390 and the R-390A. This is quite remarkable. Generally there is nothing left of a radio but the unit itself. It is quite rare that any information from the engineers actually survives. This document refers to two articles - one from the GE review and one from the Proceedings of the IRE. I scanned these two articles in for the interested parties (if any). They are both written by engineers for engineers, but it gives you some real perspective as to how things were done then. Those charts were intended for use by engineers that are designing radios. The engineer would place a straight-edge on the chart and read off some of the design parameters. Today, this would take 2 seconds in MATLAB. I typed in the equation and produced a copy of the chart in about 10 minutes. The original author probably spent weeks bending over a Marchand calculator (the original "one-armed bandit") grinding out the numbers that went into those plots.