USMC photo, via Wikimedia Commons.
In what would be the final Fourth of July of the War, American Marines parade through Paris a hundred years ago today, July 4, 1918.
July 4, 1918
Author Archives: clem.law@usa.net
1968 Stereo Headphones
If you need a pair of stereo headphones today, you can go down to the local dollar store and get a fairly decent pair. But fifty years ago, if you wanted to save a little money, you could make your own pair, as shown here in the July 1968 issue of Popular Electronics.
From the two pictures here, the construction details should be pretty obvious. Put the parts together, wire them up, put them on, and you have stereo headphones for what the magazine described as “99 cents per ear.”
Flame Speaker Science Fair Project
For the aspiring mad scientist looking for a spectacular science project that combines fire, high voltage, and loud noise, the flame speaker described in the July-August 1968 issue of Elementary Electronics should fit the bill perfectly. We previously written about how a flame can serve as a radio detector. As this article shows, it can also serve as the speaker, as the flame can be induced to emit sound. Depending on how much work you want to do, the quality of the sound can be extremely good. But even a modest investment of time can make the flame produce sound, although the simpler setups will be somewhat distorted.
The general principle is quite simple. The flame constitutes a plasma, often referred to as the fourth state of matter, made up of a cloud of positively charged atoms and free electrons. When an audio frequency signal is applied to the plasma, the positive ions and electrons move, creating a bending of the flame and room-filling sound.
The simplest arrangement is shown here. The output of an audio amplifier is fed to a transformer to step up the voltage. Nearly any transformer can be used. In this case, a bell transformer–ordinarily used to step-down 120 volts to 6 volts–is hooked up in reverse. Such a transformer can be found inexpensively on Amazon, but it’s probably possible to scavenge one. A trip to the local thrift store will probably allow you to find a “wall wart” power supply. If you can find one with an output of about 6 volts ac, then your work is done. If you can only find one with a DC output, then you’ll need to open it up and remove the rectifier.
The transformer increases the voltage of the audio sufficiently to modulate the flame. This output is connected to two electrodes, in the form or ordinary nails, which are inserted into the flame.
The ordinary combustion products do not provide sufficient plasma, so it is necessary to insert some potassium nitrate into the flame. The article recommends using an asbestos wick, in the form of “asbestos tape used to seal pipe joints in warm-air heating systems.” If you can’t find the potassium nitrate locally, it’s inexpensive on Amazon.
Of course, asbestos can’t be used today, since it would result in the haz-mat team immediately shutting down the science fair. But the article reveals that the potassium nitrate is in a solution of water, meaning that even a combustible wick would probably survive all but the hottest flames, at least long enough to do the experiment. So it seems that a normal wick, such as used in a kerosene lamp, would be more than adequate. Indeed, with some experimentation, it would seem that almost any kind of fabric could be used, as long as it begins the experiment saturated with water. Another option would be the use of welding fabric.
More advanced students will want to get rid of the distortion inherent in the simple design, and this can easily be done by providing a bias voltage. The article recommends about 400 volts. Other improvements include replacing the nails with tungsten or nichrome wire, and recommends sources. You can scavenge the nichrome wire from an old toaster, or buy it inexpensively on Amazon. The article recommends, of course, that proper precautions be taken if the high voltage bias is used. With the original simple setup, however, the experiment should be relatively safe, since no high DC voltages are used.
The original article is available from this link. Even the simplest version of this experiment is certain to take home a blue ribbon, and the more advanced version could produce truly spectacular results as the flame changes color and pulsates as it produces room-filling sound. The kid with the potato clock won’t stand a chance. You can derive some inspiration from this and other videos of flame speakers:
1948 Five Tube Portable/Auto Radio
Seventy years ago this month, the July 1948 issue of Popular Science carried the plans for this ambitious project, a five-tube set which could be used either as a portable with an internal 6-volt storage battery, or mounted under the dash, as a car radio. On the go, it would be powered by the car battery and hooked to an external antenna. But at the flip of a switch, it could be unplugged and operated on its internal battery. In either configuration, it had a vibrator power supply inside.
The internal battery could be charged from the car, or directly off AC 
power. The AC charger consisted of only a selenium rectifier and a hefty “260 ohm 100 watt” resistor to drop the voltage.
The set featured one stage of RF amplification in front of the converter for added sensitivity. Both the battery and vibrator were military surplus for high quality at a low cost.
1943 BBC Program Schedule
For a sampling of what could be heard on the shortwaves during World War II, here is the program schedule of the BBC’s shortwave signal 75 years ago today. This schedule is from the June 30, 1943, issue of the Ottawa Citizen.
For more information about the shortwave bands during the war:
- WW2 Shortwave Broadcasting
- The Shortwave Broadcast Bands During WW2
- World War 2 Shortwave Listening
- American Shortwave Broadcasting, 1941
- KGEI, GE’s Shortwave Station
Crosley Model 418 “Vanity,” 1938
Eighty years ago this month, the June 1938 issue of Radio Today carried this ad for the Crosley model 418 “Vanity,” a compact set featuring pushbutton tuning, retailing for $9.95.
The ad speaks of the brown plastic set in the most glowing of terms, but the electronics inside were very basic, although more than adequate for pulling in local stations. The set contained three tubes (plus a ballast) and was a TRF receiver with regenerative detector. More details can be found at this link. The schematic seems to show a connection for an external antenna, which would probably prove helpful for all but the strongest stations.
For $12.95, a deluxe version was available, the main difference being that the more expensive set contained “four working tubes,” meaning that it apparently had an extra RF stage.
Either set could be placed with the buttons either at the top or the bottom. In either configuration, the ad noted, the set could also be used as a bookend.
1928 Two Tube All Wave Regen
Ninety years ago this month, the June 1928 issue of Radio Broadcast magazine showed how to put together this all band two tube regenerative receiver, designed by Lieut. W.H. Wenstrom of the U.S. Army Signal Corps. The receiver was dubbed the Cornet after a Navy transmitter of the same name which was said to be simple, reliable, accessible, efficient, and flexible.
With the use of plug-in coils, the receiver had a very broad tuning range, from 10 to approximately 2000 meters. One of the triodes was used as regenerative detector, with another serving as audio amplifier. Various tubes could be employed, although the 201-A seems to be the author’s choice.
The author acknowledged that pulling in the short waves probably wouldn’t replace standard broadcasting, since the signals were subject to severe fading. But there was a lot to listen to. KDKA and WGY both had shortwave signals carrying their standard program, and the set was able to pull in England, as well as the less powerful PCJJ in Eindhoven, Holland. Weather broadcasts could be heard from NAA in Washington, then transmitting on 24.9, 37.4, and 74.8 meters. The shortwave bands were also full of harmonics of standard broadcast stations, allowing distant signals to be heard.
Amateurs, especially those on expeditions to the Poles, were a good catch, as were transocean flights by both airplanes and dirigibles.
Selling Car Radios in 1938
Eighty years ago, this unidentified service station, shown in the June 1938 issue of Radio Retailing, came up with this method of keeping customers entertained, while at the same time netting a few prospects to purchase a radio for their car. While the car was being serviced, “anything that takes appreciable time,” the attendant swung a Crosley auto radio over the door, turned it on, and invited the driver to push the tuning buttons.
The radio was mounted on two wire brackets covered with rubber. The battery and antenna were external.
The set appears to be a Crosley model A258 Fiver Roamio.
W9ZYB, Norwood Park, IL, 1938
Shown here on the cover of the June 1938 issue of Radio News is the well equipped station of Bert Heuvelman, W9ZYB, of Norwood Park, IL, a suburb of Chicago. The attractive homebrew transmitter, mounted on a panel of blue linoleum, consisted of a 6F6 crystal oscillator, T20 and T55 buffers, with two T200’s in the final running a kilowatt. The crystal mike was fed to a pair of 2A3’s driving a pair of 822’s in the modulator. Band switching enabled fast band changes. A Hallicrafters receiver was used, and the output was constantly monitored with an oscillograph and modulation meter.
Assisting Mr. Heuvelman is Miss Naomi Anderson, a professional model borrowed from the magazine’s sister publication, Popular Photography.
The magazine notes that the photo was captured with the help of over 3000 watts of flood lights illuminating the scene, and was the work of Henry F. Kroeger, Jr., of Chicago, who used a Kodak Retina II.
Soldering: So Simple A Child Can Do It
For those who believe that soldering is just too difficult, we offer this counter-example from the June 1938 issue of Radio News. The pictures bears only the caption, “set repairing carefully done by experienced servicewoman.”
For those who believe the cost of tools is just too great an investment, we offer the following perfectly adequate soldering irons, even easier to use than the one this young woman mastered eighty years ago: