This movie was made in 1941. All radios of that era amplified the signal through a series of electric vacuum tubes, each of which had a heater circuit and consequently consumed as much energy as a regular light bulb. I refuse to believe that in that pre-transistor epoch (before 1947) anyone had a radio as small and light as one brought into the switchboard scene by the cadet.
shareActually battery operated vacuum tube radios were the norm until 1928 when Ed Rodgers of Toronto invented the first one to operate well on household AC. The problem was the hum from the 25 cycle power lines of the day. They made radio sounds unbearable to listen to. Rodgers (now the Canadian telecommunications giant)fixed that problem with his improved vacuum tube system.
At 25 cycles lights flickered and things hummed loudly. 60 cycle power replaced that much later and was much more efficient.
Well, believe it, because the film came out in 1942!
shareThere were small hearing aids in 1938: https://beckerexhibits.wustl.edu/did/20thcent/part2.htm
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