English: Homemade single tube Armstrong regenerative shortwave radio receiver using construction apparently dating from 1930s-1940s. The regenerative receiver design was abandoned by commercial radio manufacturers in the 1920s due to its tendency to radiate interference, but due to its simplicity and low cost continued to be built by radio amateurs for shortwave listening until World War 2. The controls on the front panel are: (left) regeneration control, which increased the feedback to the tube; (bottom center) filament rehostat, which controlled the current to the filament of the triode vacuum tube, serving as a volume control; (right) tuning capacitor.