Seventy-five years ago this month, the March 1949 issue of Radio News included pointers for those interested in getting started in Amateur Radio. In just a few years, it became easier to get started, with the introduction of the Novice license, which required code at only 5 words per minute. But in 1949, to get on the air, you needed to pass the test at 13 WPM. But the magazine gave pointers on how to do it, and reminded readers that hundreds of thousands of hams had managed to do it.
The plans for this handsome two-tube set appeared 80 years ago this month in the March 1944 issue of Radio Craft magazine. The author had a broken midget set with a cracked case, one bad tube, and some loose connections, but he was able to use the parts to make this portable TRF set.
For a cabinet, he found some clear plastic. The result, despite wartime parts shortages, was a radio almost as good as the donor.
The advanced student looking for a spectacular science fair project can’t go wrong by constructing the 60-cycle repulsion coil resonance engine described in the March 1964 issue of Popular Electronics. Essentially, it’s a coil and capacitor tuned to be resonant at exactly 60 Hz. The cover photo above shows the coil being used to repel a two-inch piece of aluminum tubing.
The device is called an engine because it can be used as shown to the left, with a reciprocating piston driving a flywheel. As with any single piston engine, to get started it requires a spin to get started, unless it happens to be in just the right spot.
The author suggests a number of other experiments that can be done with the device, all of which we guarantee will bring home the blue ribbon.
A hundred years ago this month, the March 1924 issue of Radio News showed the holy grail of crystal sets: One that would provide the elusive loudspeaker volume without any tube amplification. It didn’t require any electrical power, but as the hand crank indicates, it did require mechanical power.
The device was dubbed the Frenophone, and was invented by S.G. Brown of the company S.G. Brown, Ltd., of England. It worked as follows, referencing the diagram at left:
An ordinary Brown telephone receiver, A, with adjustable magnets, is attached to a metal arm pivoted at B, and weighted at the end with counterbalance C. To the reed D and the receiver are attached the steel needle E to whose end is fastened a small disk F covered on the bottom with cork. This small disk is directly above a perfectly level glass plate G. The glass plate, in turn, is mounted on the shaft of a phonograph motor so that it may be slowly revolved. The disc F, as shown in Fig. 2, is suspended by threads H near the edge of the glass plate G. The two threads terminate at the center of the diaphragm L which is the diaphragm of the loud speaker.
According to the magazine, the instrument required very fine adjustment. But once it was set up, it worked satisfactorily, and frequent adjustment was not necessary. If you want to see one in person, you can do so at this London museum.
Eighty years ago, these gentlemen are disassembling an old radio to salvage the parts within. There was a war going on, and those old parts would provide many useful materials. The March 1944 issue of Popular Mechanics reminded them to unsolder all fixed resistors and capacitors, rather than clipping the leads. It also reminded them to save the coils, sockets, and screws in separate compartments in their junk boxes.
If a scout 70 years ago needed a boat, he could make this one himself, thanks to the plans found in the March 1954 issue of Boys’ Life. Dubbed the “Nee Deep”, the 8-foot punt had a carrying capacity of two to three persons. It could be powered by oars, or a small outboard motor of less than 3-1/2 horsepower.
Most of the boat was pine, with the bottom being a sheet of 1/4 inch exterior plywood.
Of course, don’t follow the example of the scout in the illustration. When you’re out on the water, you should have (and preferably wear) a Coast Guard approved personal flotation device.
Some links on this site are affiliate links, meaning that this site earns a small commission if you make a purchase after using the link.
The fashionable headgear shown here from a hundred years ago is being donned by an engineer at WDAP in Chicago. The station had these so that the quality of the station’s transmission could be checked at any time anywhere in the studio. The crystal set was mounted on a pair of headphones, which meant that there was no need to sit down at a standard receiver.
Later that year, the station was purchased by the Chicago Tribune, which changed the call letters to WGN, for World’s Greatest Newspaper.
These images appeared in the March 1924 issue of Popular Mechanics.
Eighty-five years ago, radio repairman Lewis P. Evans of Chicago’s Evans Radio Laboratory brought along a camera on every service call. He would snap a picture of the house, or if he was lucky, a picture of a child, or even the family dog.
He would hold on to the pictures for a few months, and then send them to the woman of the house, with the shop’s address on the back. He reported that a woman can’t resist a picture of her own home or someone in her family. The picture would be saved, or perhaps placed in the family photo album. And when the radio needed service, they would know exactly where to find the shop’s address.
This feature appeared in the February 1939 issue of Radio Retailing. According to this 1936 newspaper advertisement, the shop’s address (presumably the one on the backs of the photos) was 7152 S. Exchange Ave.
This schematic for a code practice oscillator appeared in QST 70 years ago this month, February 1954. The observant reader will notice that something seems to be missing.
That’s right. There’s no apparent source of B+ power. The only power connection is to the filament of the tube. But it works anyway! According to an editor’s note, the circuit shows 0.2 volts between the cathode and plate, derived from the initial velocity of the electrons.
According to the same note, the only other circuit that works without any apparent plate voltage is a Tri-Tet crystal oscillator, This is explained in more detail in an article in the May 1941 issue of QST. According to that note, the oscillator “will run merrily without plate voltage from an external source so long as the circuit is complete.”
This code oscillator was designed by long-time ARRL staffer Lew McCoy, W1ICP, who then held the title of Technical Assistant. He noted that the electric buzzer was the traditional method, but “if you don’t live alone, the sound of an electric buzzer may soon grate on the nerves of the family or neighbors.” This inexpensive circuit allowed practice while still preserving peace at home.
The novel method of powering the oscillator meant that it could be built for less than six dollars, less than half the cost of commercial code oscillators. And after licensing, those parts could undoubtedly be put to use in other projects.
McCoy noted that while the circuit worked with all 6J5 tubes he tried, it was possible that a particular tube might not. In that case, the advice was to try another. He noted that the 6F6 pentode he tried, with plate and screen tied together, also worked.
The oscillator took care of the beginner’s need for sending practice. For receiving, he pointed out the W1AW code practice sessions, but also included a list of other stations with scheduled code practice. Many of these were operating on 10 meters. For example, W0BOL was sending code practice on 29.2 MHz Tuesday and Wednesday evenings from 1130 Delaware Avenue, St. Paul, MN.
Eighty years ago this month, the February 1944 issue of Radio Craft gave some description of the automatic gun director system illustrated here. The system consisted of a computer (undoubtedly analog) that directed the gun exactly where to fire. The path of the plane was plotted by two telescopes, whose operators kept the plane in the cross hairs for a few seconds, to plot the aircraft’s location, speed, and direction. Height was measured in a similar manner, and the computer had inputs for wind direction and velocity, muzzle velocity, and air pressure. The result was a gun that was able to aim itself to the spot where the plane would be when the shell arrived.