Sixty years ago this month, the September 1960 issue of Popular Electronics showed how to put together this one-way carrier current intercom. It could be used to listen to the nursery, garage, or other room, anywhere in the house. The transmitter was a simple one-transistor oscillator, using a speaker as the microphone. It sent the signal through the house wiring to another room, where a pickup coil was plugged in and placed near a radio set to a clear spot at the bottom of the dial. Despite the low power, this hookup allowed the signal to be monitored anywhere in the house.

According to the magazine, the parts cost was about $10.

This young woman is seeking her fortune with a metal detector she put together herself, according to plans contained in the September-October 1980 issue of Elementary Electronics (which had recently merged with Science & Electronics, as noted on her shirt). The article mentioned that the biggest downside of the treasure hunting hobby was the amount of money needed for the equipment, which often exceeded the value of the treasure. But this inexpensive circuit, which could run for a year on a single 9 volt battery, was a good tradeoff between economy and sensitivity. The set was able to locate a penny buried 3-5 inches deep.

The circuit included three inductance coils, two of which were balanced to have a net current of zero passing through them. When a piece of metal came within the field, the inductance of one coil changed, causing the circuit to oscillate. The circuit consisted mostly of an integrated circuit audio amplifier which was wired up to oscillate when the inductance was just right.

The article cautioned treasure hunters that practice was the key, and they should see how the instrument reacts to various pieces of treasure given local soil conditions.

The young man shown above is now close to being a centenarian, but 80 years ago, he was buying some radio parts from his friendly local radio dealer. He was going to get his money’s worth out of those parts, since he planned to re-use all of them in several different projects, the first of which appeared in the September 1940 issue of Popular Science.

The total expenditure for all of the projects would be $8.95, and this month, he was purchasing a number of components, including two tubes, a pentode-triode 25B8GT and a pentode-rectifier 70L7GT. This month, he was going to make the two-tube receiver shown below. This month, only one half of each tube would be used. The 70L7GT served as rectifier, and the pentode section of the 25B8GT was regenerative detector. In future months, the circuit would become more elaborate.

The article noted that the capacitors could be soldered in place, but since the resistors would need to be moved around, it was best to attach them using clips so that the leads would be preserved.

The parts list reveals that this version of the set would tune 100-570 meters, meaning that it would cover the standard broadcast band, plus a few interesting signals higher in frequency.

Eighty years ago, this radio enthusiast/sports fan was able to attend the game and listen to the play-by-play broadcast from the stands, thanks to this one-tube pocket portable, described in the September 1940 issue of Popular Science. The set was billed as being only a little larger than a tobacco tin, and was constructed from cigar box wood. The antenna was a loop wound around the box, and it was said to be able to pull in stations up to fifty miles away.

The circuit was superregenerative, and used a miniature 958 tube, which is likely unobtainium today. The B battery consisted of four penlite cells, and the A battery was a normal flashlight battery.

A century ago this month, the cover of the September 1920 issue of Radio News featured this man teaching the art of radio to his companion.

The issue also featured an article by Marianne Brown, 2AOA, whom we profiled in an earlier post, from the magazine’s April 1920 issue. Her training was much more formal than the woman shown on the cover. With the U.S. in the war, she decided to do her part by getting trained as a radio operator, and then waiting for the government to put her to work. Unfortunately, that never happened, but she did secure a position in the testing department of the Marconi Company, and she writes about her experiences there as “one of the gang.”

The plans for this 2-transistor pocket portable receiver appeared in Radio-Electronics magazine 60 years ago this month, September 1960. The circuit was the result of prodding from the author’s son to produce a pocket radio in time for the World Series, hence the name of the set, the World Series Special.

The author noted that pocket portable typically came in two categories–they were either superhets that were difficult and expensive to build, or else simple one or two transistor sets that wouldn’t pull in anything without a 50 foot outdoor antenna. This set was a good compromise, since it would pull in the strong local stations (presumably including the one that was broadcasting the World Series) without an external antenna.

The circuit had a regenerative RF stage, followed by a crystal detector. That was followed by two stages of audio amplification. It used two transistors, the venerable 2N170 NPN, and the 2N107 PNP. The 2N170 was reflexed to serve as both RF amp and first AF stage. The 2N107 was the final audio transistor. The article stressed the importance of using a good earpiece, since a sensitive one would have much better volume. Regenration was fixed, and there was a separate volume control. It was powered with a 7.5 volt mercury battery that was soldered in place, since the author apparently had faith in his son to turn the radio off when not in use.

The author noted that layout was not critical, with one exception: It was important to keep the battery as far away as possible from the antenna coil.