Sixty years ago this month, the October 1955 issue of Popular Electronics carried the plans for this one-tube broadcast set.  Even though it had only one tube, it was capable of driving a loudspeaker, thanks to the fact that the tube, a 1D8-GT, was actually three tubes in one.  In consisted of a diode, which was the radio’s detector, a triode, which served as the first AF stage, and a power pentode which drove the speaker.

So even though the set used a single tube, it was the equivalent of a crystal set with two stages of audio.  The article notes that the set gave good performance on strong local stations with just a few feet of wire for an antenna, and that it was able to pull in more distant stations with an outside antenna and ground.

The set was powered by a 1.5 volt A battery and a 90 volt B battery.  The pictorial diagram here, more than the schematic, shows the simplicity of the little set.

A piece of wood, 8-1/2 by 5 inches, serves as the base, and the controls and speaker are mounted in place with right-angle brass brackets.  Terminal strips are used for the battery, antenna, and ground connections.

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Modern bridge rectifier.

Today, if you need a rectifier, it’s a fairly easy matter to buy one. One like the the one shown here will handle 1000 volts and 50 amps, and will only set you back a few dollars. Smaller ones for transistorized circuits can be had for pennies.

In 1935, however, it was a different matter, and parts were not so readily obtainable. Radios would typically use a vacuum tube rectifier, and for other applications such as battery chargers, a “dry” rectifier would commonly be used. In the 1935 Allied Radio Catalog, a “dry” rectifier has a catalog price of $3.73. A full-wave vacuum tube rectifier, the Raytheon BH, has a catalog price of $2.46. These prices don’t sound like a lot, but this was the middle of the Great Depression. And a silver dollar then was worth about the same as a silver dollar today. The only difference is that back then, you had to hand over an actual silver dollar for each dollar on the price tag.

1935 homemade copper oxide rectifier.

It’s not surprising, therefore, that someone might decide to make their own. And Popular Mechanics 80 years ago this month, October 1935, showed how. It included circuits for a battery charger, a 6-volt “A” battery eliminator for a radio, and an A.C. voltmeter.

The finished product wasn’t particularly efficient. It required 16 volts AC in order to put out 6 volts DC. A rectifier consists of two dissimilar metals, and in this case, it made use of copper washers, one side of which was oxidized to form copper oxide. The washers were sandwiched between lead washers to form the necessary junction and keep them tightly fixed together.

The copper was oxidized by holding it over a gas flame, either from a bunsen burner or a gas stove. Then, it was left to cool, after which one side was carefully sanded with emery cloth. The pieces were then sandwiched together, with bakeline on the outside layer. The finished product was a bridge rectifier consisting of four diodes.

Building your own rectifiers was nothing new. In the early days of radio, even bigger rectifiers were needed. As I reported in an earlier post, in 1923, T.E. Nikirk, 6KA, solved the problem by building a rotary rectifier. It used a 3600 RPM synchronous motor, meaning that the motor revolved 60 times per second, just like the AC current. Attached was a spinning disk which served to reverse the polarity twice per cycle. In comparison, the 1935 “dry” rectifier seems tame.  Interestingly, the silicon rectifier at the top of the page probably has about the same ratings as 6KA’s massive spinning contraption.

1909 Chemical Rectifier.

More common in the early days of radio was the “wet” chemical rectifier, such as the one shown here from a 1909 issue of Popular Electricity.
It consisted of diodes made out of glass jars, each containing lead and aluminum electrodes, in a solution of ammonium phosphate.  A similar rectifier for use in a CW transmitter is described in a February 1921 QST article by P.J. Furlong, 1FF. For the electrolyte in his eight jelly jars, he used Twenty Mule Team Borax.

The modern silicon rectifier seems like a trivial component, and I don’t suppose I would try to save a few pennies by making my own.  But it comes under the category of things that it’s nice to know are possible.  You can make your own rectifier, and these old pioneers of electricity and radio showed that it was possible.

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Dr. Lee DeForest is, of course, best known as the inventor of the audion, or triode tube. But he had many other inventions to his credit. For example, a few months ago, we featured the 1950’s Arizona fallout shelter/ham shack of William A. Rhodes, W7PYH (later W7KLA). It turns out that DeForest was co-inventor along with Rhodes of an electronic light amplifier with applications in astronomy and television.

And 85 years ago, we see what some might consider to be DeForest’s greatest invention, the “ANTI-AD,” a remote control device for squelching annoying radio advertisements. DeForest describes the device in the September 1930 issue of Radio News, wherein he laments “the tendency of the present radio broadcast programs to degenerate more and more into crass commercialism and to devote a steadily indreasing proportion of the time to exploiting the merits of every conceivable commondity from tooth-paste and cigarettes to household furniture and diamond rings.”

While remote control sets were coming onto the market, DeForest notes that they came with the nuisance of having a cable between the radio and the easy chair, over which “the missus and the children invariably trip.”

Instead, DeForest came up with the entirely wireless solution to the problem. The radio’s antenna lead is connected to the device shown here, which contains a selenium cell, one tube, and a relay. When the offending commercial interrupts the program, the listener simply shines a small flashlight, “which can be had in very ornamental form” at the device. When the light hits the photocell, the antenna is disconnected and the radio silenced. The relay had a time delay which could be set to correspond to a typical commercial length.

“When the announcer begins to tell the health benefits of his cigarette,” the listener simply gives the unit a quick flash, knowing that at the approximate end of the commercial, the device will reset and the program resume.

DeForest concludes that the “Anti-Ad adds to real radio enjoyment and greatly extends the number of hours throughout the month when the radio set is in operation. It should therefore be received with open arms by the entire radio industry.”  But perhaps it wasn’t, since ten years later, he wrote in an open letter to the National Association of Broadcasters:  “What have you done with my child, the radio broadcast? You have debased this child, dressed him in rags of ragtime, tatters of jive and boogie-woogie.”

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Eighty years ago, the September 1935 issue of Radio News described this “CQ Key,” an early memory keyer, by Ed. Glaser, W2BRB. It’s driven by a windshield wiper motor acquired from a junkyard for a dollar, and can be used to repeatedly call CQ. In the illustration here, a disc sending TEST is installed, with the disc at the upper right used for calling CQ. If you read counterclockwise starting near the top, you can see that it sends, “CQ CQ DE W2BRB” repeatedly.

The author notes that he initially hooked the disk directly to the motor and tried to control the speed with a rheostat. The 6-volt motor performed well down to 4 volts, but below that voltage the motor ran unevenly or sometimes stopped. Therefore, he described an arrangement with a 4:1 gear ratio that proved satisfactory.

The author reports that the setup performed well, and that he had run the key for hours on end on 5 meters and 75 centimeters, presumably running early beacons on VHF and UHF.

The disc is made of 3/16 inch bakelite, 2-1/2 inches in diameter. The contacts were taken from an old relay and mounted so that they would be closed by the rotating disc. The author notes that this arrangement is sufficient for keying a couple hundred volts, but for higher voltages, a relay would be necessary. The keyer was “programmed” with a hacksaw and file, and the author reported that the process took a couple of hours, with the work on subsequent discs going much faster.

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Ninety years ago today, the September 26, 1925, issue of Radio Digest announced the winner of the coveted title of Miss Radio 1925, namely, Miss Rena Jane Frew of 334 Fifth Street, Beaver, Pennsylvania.

She won a silver cup and a trip to New York City where the award was presented at the Radio World’s Fair by Governor Al Smith. The contest was billed as one to “discover the ‘Diana of Radio’–the most successful and enthusiastic hunter of distant stations.”

Miss Frew was twenty years old.  The magazine reported that she had been an amateur since the age of 14, and reported the call sign of her station as 8ME.  According to the 1922 call book, that call was licensed to Beaver High School.  That same call book does not show any call under her name, meaning that she apparently did not have her own station.  According to the Harrisburg Evening News, Sept. 12, 1925, she did have her operator’s license, and states that she was the first licensed operator in Pennsylvania, and probably the first east of the Mississippi. During her freshman year, she taught a class in wireless.  In fact, she was well known to the hams in the Pittsburgh district, who referred to her as the “Little Ladybug.” After broadcasting became popular, she tuned in every principal station in the U.S., Canada, and Puerto Rico, as well as foreign stations.

Among her other duties, according to the Chicago Tribune, Miss Frew attended the Chicago radio show as one of the chief guests.

In 1927, she was teaching, and as one of her former eigth grade students recounts, she headed that school’s radio club.

According to her sister’s obituary, she became a special education teacher in Rialto, California, and died on June 30, 1996.  A photo of the cup being presented by the governor is available at this link.

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85 years ago, the September and October 1930 issues of Popular Mechanics showed how to build this four tube shortwave receiver which tuned 15 to 195 meters “without plug-in coils. Instead, it had a four-position band switch, which made it “no longer necessary to shut off the set and take it apart in order to change from one wave band to the other.” The regenerative receiver employed two 224 tubes in the RF section, followed by a two stage audio amplifier using a 201-A and a 112-A. It was set up for headphone use, although provisions were made for adding an external loudspeaker. In addition to the band switch on the left, the front panel had tuning and regeneration controls. The chassis was made of brass, with a bakelite front panel.

The author’s lovely assistant makes some finishing touches to the cabinet.

The author reported that the set was tested in Chicago, and pulled in over the course of a few hours numerous amateur stations, including the seventh, fourth, fifth, sixth, second, and ninth call districts. Due to “unfavorable atmospheric conditions” during the test, no foreign stations were received, but it did pick up broadcasts from WGY.

The author was Frank L. Brittin, W9DCX, who was with the magazine from 1920 until his death in 1955. From Springfield, Illinois, he ws first licensed in 1915 and was an early member of the ARRL. His death is noted in the magazine’s July 1955 issue.

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