Eighty-five years ago this month, the April 1941 issue of Popular Science showed how to build this receiver. It’s essentially a crystal set, but instead of a crystal, it uses a 25Z5 rectifier tube. Since there is no B+ voltage in use, the magazine assures that there will be absolutely no hum. Also, it’s safe to ground the set, because there is no connection to the power, other than to light the filament.

Instead of 25 volts, the filament is powered with 5 or 6 volts, which is obtained by dropping resistors, and/or a “curtain burner” cord.