via HACKADAY: Inside a 1940’s Spy Radio

The RCA CR-88 was a radio receiver made to work in top-secret government eavesdropping stations. As you might expect, these radios are top-of-the-line, performance-wise, at least when they are working correctly. [Mr. Carlson] has one on his bench, and we get to watch the show on his recent video that you can see below.

Interestingly, [Mr. Carlson] uses some Sherlock Holmes-like deductive reasoning to guess some things about the radio’s secret history. The radio’s design is decidedly heavy-duty, with a giant power transformer and many tubes, IF transformers, and large filter capacitors.

The underside of the radio reveals neat wiring and some big metal shields. The metal shields and filters have a very specific purpose. The radio was probably in a bank of radios, and you don’t want them interfering with each other. In addition, you might not want someone tracking your super secret listening post by its RF emission. [Mr. Carlson] shows on the schematic how the designers reduced unwanted emissions from the radio.