Monthly Archives: February 2019

1959 Sleep Learning

The February 1959 issue of Popular Electronics carried this handy device to facilitate sleep learning. As a youth, my attempts at sleep learning were frustrated by (in addition to the fact that it apparently doesn’t work) that the only tape recorder I owned had a very limited amount of record time. So chances are, the tape would have played to completion before I even fell asleep. And it would play only a single time.

One of these devices would have solved that problem. The exact details (as well as the price) were lacking, but the Electronic Educator, sold by the Sleep Learning Research Association of Olympia, Washington, allowed the use of a continuous tape cartridge with between 1 minute to 2 hours of tape. In other words, the lesson would play all night, and you would wake up having mastered the material.

1949 Geiger Counter

Seventy years ago, prospecting for uranium was seen as a good way to get rich, and the February 1949 issue of Popular Mechanics showed how to do it. The issue included an article with pointers for the beginner, and also featured a construction article about how to build a Geiger counter. The electrical circuit was simplicity itself, and the unit was built into a metal lunch box.

The only caution involved the 900 volt power supply, supplied by three 300 volt dry cells. The article did caution not to touch the terminals.

Electronics in the Classroom: 1959

The student and instructor shown here are demonstrating properties of sound, thanks in part to $300 million in federal funds made available to high schools by the Science Education Bill. The February 1959 issue of Radio Electronics gives some ideas of how electronic equipment can be worked into the curriculum. The article suggested that many phenomenon, such as sound, can be converted into electrical energy by appropriate transducers. Here, a scope, audio amplifier, and giant VTVM are used to demonstrate properties of sound.

RCA Model 97K2, 1939

Eighty years ago, people still dressed up to listen to the radio, as shown by this RCA ad from the February 6, 1939, issue of Life magazine. This listener is tuning in a standard broadcast station on her RCA model 97K2. The set also tuned two shortwave bands, 2.3 – 7 MHz and 7 – 22 MHz, but we can see that she is pushing one of the six preset buttons, which were for the standard AM band. In fact, we see that she is pushing one of the two rightmost buttons, which could cover approximately 890-1500 kHz. The first two buttons could be set for 550-950 kHz, and the middle two buttons could be set for 690-1225 kHz.

The set had the following tube lineup: A 6K8 served as first detector and oscillator, with a 6K7 serving as IF amp. A 6H6 served as second detector and AVC, with a 6F5 and 6F6G as audio amplifiers. A 6U5 “magic eye” tube served as tuning indicator, and a 5Y5G in the power supply served as full-wave rectifier. The set featured a dynamic speaker.

1934 “Globe Trotter” Two Tube Regen

Eighty-five years ago this month, the February 1934 issue of Short Wave Radio magazine carried the plans for this two tube (plus rectifier) receiver. Dubbed the “Globe Trotter,” the set covered shortwave and the standard broadcast band thanks to plug-in coils.

The set used a type 57 tube as regenerative detector, with a type 2A5 tube serving as audio amplifier to drive a speaker. A type 80 full-wave rectifier rounded out the tube compliment.

The set would be difficult to duplicate today. It employs a transformer which is probably unobtainium. The hardest to find component might be the dynamic speaker. Instead of a permanent magnet, this type of speaker used a field coil, which magnetized the speaker, and also served as a filter inductor for the power supply.

1944 Expedient Winter Clothing

Seventy-five years ago this month, the February 1944 issue of Boys’ Life gave some pointers on how to keep warm on a budget. The burlap foot coverings are the same general idea as what we previously offered for expedient winter footwear. And if your jacket isn’t quite warm enough, then lining it with a few layers of newspaper will surely do the trick.

Science Fair Idea: Magnetostriction

Students looking for an interesting science fair project to illustrate a concept that the science teacher has probably never heard of can’t go wrong with this simple experiment demonstrating the principle of magnetostriction. This property causes certain materials to change shape and dimensions during the process of magnetization. The effect was first noted by James Prescott Joule in 1842.

The effect is quite small, but the ingenious experiment shown here will detect the change in length of the iron rod. One end is placed on a roller, which might be as simple as a wooden dowel. The dowel has a rather long pointer affixed to detect the small changes in length.

The magnetic field is induced by winding insulated wire around the rod. It’s powered by two old-school dry cell batteries, but two modern alkaline D cells will work just as well or better. The construction of the experiment will be neater if you use a battery holder.

Chances are, the science teacher has never heard of magnetostriction, and he or she will be quite impressed that you were able to induce a measurable change of length in the seemingly solid iron rod.

The project appeared in Popular Science 80 years ago this month, February 1939.

Groundhog Day 1919

Happy Groundhog Day from OneTubeRadio.com!

The clipping shown here, from the Harrisburg Telegraph, August 25, 1919, was obviously from several months after Groundhog Day. But it seems likely that the groundhog cached his supply on February 2, only to be discovered later.

But in any event, in August, Antonio Bellini was groundhog hunting and spotted a groundhog which ducked into its hole. Mr. Bellini began to dig it out, only to discover six quarts of whiskey hidden in the hole.

1944 Tape-Operated Code Sender

The gentleman shown here is practicing copying Morse Code that the woman is literally cranking out for him, thanks to this automated code sender from the February 1944 issue of Popular Mechanics.

Today, it’s a relatively trivial matter for a computer to generate code, such as with this online code generator. But 75 years ago, saving a message for later replay probably involved paper tape. This machine allowed you to play such tapes, using a contact made of distributor points from a car. The tape could be prepared (using ticker tape) with a hole punch, or you could use commercially available tapes (probably Instructograph tapes).

The device could be powered with a crank, or with a sewing machine motor controlled by a rheostat.