Eighty-five years ago this month, the May 1940 issue of Popular Science showed how to put together this four-tube (1A7GT, 1N5GT, 1H5GT, 1C5GT) portable receiver. As shown in these illustrations, it was guaranteed to enhance any activity at home or on vacation. Powered by a 1.5 volt A battery and 90 volt B battery, the superheterodyne design could pull in stations 100 miles away during the day, or 500 miles at night, with only the built-in loop antenna. For greater DX, an outside antenna could be connected.

The magazine provided proof, in the photo at left, that the set weighed in at a mere eleven pounds.

The plans for this handsome one-tube receiver appeared a hundred years ago this month in the May 1925 issue of Popular Science. The set was said to be ideal for the beginner, but still boasted long-distance reception. Regeneration was controlled by a variable capacitor, and this was said to reduce squealing, by virtue of the fact that only RF, and not audio, was fed back. The set called for an antenna of 75-100 feet. In testing, the set pulled in Chicago from a less than ideal location in New York.

Back in the day, kids were warned about things like not listening to the radio in the bathtub, or the importance of wearing shoes in the basement. This was because caution was warranted around many electrical devices, especially the “AC-DC” radio, which was the most common design.

These circuits were such that one side of the electrical cord was often connected directly to the chassis. For some semblance of safety, there were some precautions taken. First of all, the cabinet was often made of wood or plastic, which insulated the chassis inside. Even then, though, there was often a screw visible in the back. In some cases, the connection to the chassis was through a capacitor, although that could eventually become leaky. So taking your five-tube radio into the bathroom probably wasn’t a good idea.

This hint for adding a bit more safety appeared in Radio-Electronics 75 years ago, May 1950. If the plug is plugged in with the correct polarity, then the risk of shock is minimized considerably. These days, if you’re restoring an old radio, it’s a good idea to add a polarized cord and/or a three-prong plug.  Even so, it’s probably best not to use it in the bathroom or near the kitchen sink.

Sixty-five years ago this month, the May 1960 issue of Radio Electronics showed that a portable AM radio can made a surprisingly good direction finder. The loop antenna is typically directional, and has sharp nulls as it is pointing directly at the station. You can use this effect to determine your location quite accurately by taking readings from two stations, and plotting them on a map from the station’s known location. The lines should intersect at your exact location.

I have done this before, and by using local AM stations, I can plot my exact location within a few hundred yards. At night, by using distant stations, I can determine my location within a few tens of miles.

Since the radio’s antenna is typically parallel with the case, you can do a good job of plotting by simply laying the radio on the map, and using it as a straight edge. But the article shows a more refined method. You can use an HO-scale model railroad turntable and mount the radio on that. This provides a handy crank, and you can calibrate the dial with exact directions.

A further refinement was to obtain a surplus pelorus and mount the radio in that. This would allow very exact visual bearings to the station.  Unfortunately, there don’t seem to be many surplus peloruses (yes, that’s the correct plural) in circulation these days.

Once you know your position, you can navigate directly toward one of the stations by placing your radio parallel with your boat, and simply keep the signal nulled.

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