Wartime parts shortages were undoubtedly the inspiration for these two crystal sets from the January 1944 issue of Popular Mechanics. While commercial parts could be used, from the junk box, salvaged from an old radio, or from a mail-order house, the article showed how to make most of the parts. The article notes that the newcomer needed only a good set of headphones to build either set from scratch.

The first set, shown above, omitted a variable capacitor, as it used a variometer for tuning. It did require one fixed capacitor, but the article shows how to make one using copper foil and either mica or wax paper.

A commercial fixed crystal can be used, but the article also shows how to make one. The crystal is mounted inside an old tube base and sealed with wax. The use of an old 4-prong tube socket meant that a commercial fixed crystal could be substituted at a later time.

The second set, shown above, featured a variable capacitor for tuning, which was constructed “book” style. The top plate, made of spring brass, was hinged and moved up and down from the lower plate.

The sets were said to have a range of about 25 miles.

Seventy-five years ago this month, the December 1943 issue of Radio Craft included a description of this light-phone reportedly in use by the Germans.

The set could operate in three modes: white light, red light, or infrared. Obviously, simple morse signalling was possible, but the beam could be modulated with audio.

The article noted that the applications of the device were rather limited, but wondered whether the Allies would be adopting a similar system at some point.

Just because there was a war going on didn’t mean that you couldn’t listen to the radio while riding your bicycle, as shown in Popular Mechanics. December 1943.

The set was billed as a “big town” bike receiver, and the article pointed out that it would pull in the local stations “as you ride around in any city where powerful stations are located.” The set itself was just a crystal set, using a fixed detector. The set was mounted in a tin can, which in turn was afixed to the bike. The tuning condenser and headphone connections were conveniently accessible while riding, and a whip antenna was used to pull in the strong local signals.

Unfortunately, the magazine doesn’t seem to provide any details as to what’s going on in this picture, from the cover of Radio News, November 1943.

But obviously, these men are mastering the finer points of voice communication.

75 years ago, wartime shortages meant that meters were not readily available. The November 1943 issue of Popular Mechanics offers this tip for checking whether high voltage is present. A small capacitor (.25 to 2 uF, 400 volt) has spaghetti tubing placed over the leads, which are connected where the high voltage is being tested for. The capacitor is then removed and the ends shorted. A spark indicates the presence of high voltage.