08-21-2024, 01:55 PM
Copper-oxide diodes existed at that time. I own a Triplett 1167-A set tester ca. 1935 which uses a small copper-oxide stack as the voltmeter rectifier for measuring AC. I doubt that is what is shown on the schematic, though.
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/