This one tube radio is shown in an ad from 90 years ago, from the December 1924 issue of Radio News.  The ad for the National Airphone Corporation features the Monodyne, billed as “one of the most radical advances in Radio engineering. Parts heretofore considered essential are omitted with no loss of efficiency.” One customer reported hearing a broadcast from over a thousand miles away “like talking over the back fence.” It sold for $10, without the tube, headphones, or battery.

I haven’t been able to find any schematic or other details about this little radio. gifarmer.com has some information, including a photo of a nice surviving example. The radio came with two coils, one to cover 150 to 400 meters, and the other to cover 500-1000 meters. That works out to 750 kHz through 2 MHz, and 300 to 600 kHz. Presumably, those band edges were not exact, since there were stations between 400 and 500 meters, such as WLW on 423 meters (710 kHz) and WMAQ on 448 meters (670 kHz).

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