While Fido keeps a watchful eye, the father-son team here is putting together the one tube regenerative shortwave set shown 80 years ago this month in the April 1938 issue of Popular Mechanics.

The set ran on three flashlight batteries. Two of them in series provided the 3 volts of B+ necessary to run the type 49 tube, with another powering the filament.

With four plug-in coils, the set covered 18 to 200 meters. A good antenna and ground were required, as were high-impedance headphones. But as evidenced by the QSL cards shown in the illustration above, the simple circuit was capable of pulling in DX.