Monthly Archives: December 2016

1936 Inter-Office Intercom

1936decradioretailingCallers to this 1936 factory were never asked to hold the wire. With this intercom from Sound Systems, this efficient information clerk was able to reach anyone in the plant instantly. The photo appeared in the December 1936 issue of Radio Retailing, which reminded readers that inter-office communication systems saved footsteps and sped up routine.


1941 Recordgraph


Seventy-five years ago this month, the December 1941 issue of Radio News carried a detailed description of a sound recording system that, while very sophisticated for its time, was quickly superseded by magnetic recording, first on wire, and then on tape. The magazine described the sound-on-film recording system employed by the Recordgraph, shown above. This machine recorded sound on 35 mm film, but did not involve photography. Instead, the instrument was a sophisticated phonograph, mechanically carving a groove into the film, which did not have any photographic emulsion. Instead of a disc or cylinder, the grooves were cut into the film.

The great advantage of this system was the large amount of material that could be recorded. The market for the system was law enforcement, which could make sound recordings of, for example, a telephone line. The machine could be switched on automatically whenever a phone was off the hook or a radio carrier present. The film ran in a continuous loop at 20 feet per minute. The film could hold 100 tracks, meaning that only 6-1/4 feet of film were necessary for an hour of recording.

A well preserved example of the Recordgraph can be seen at this link.  A similar system, the Tefifon, was commercially produced in Europe, and can be viewed here:

The Recordgraph apparently saw at least some use by law enforcement.  The record from this 1949 New York case includes testimony describing how the device was used for telephone monitoring.

While the sound quality of this system is remarkably good, it was quickly supplanted after the war by magnetic recording, first on steel wire and then on magnetic tape.  The greatest advantage of magnetic recording was that the wire or tape could be erased and re-used indefinitely.


1925 Four Tube TRF


The August 1925 issue of Popular Mechanics carried the plans for this four-tube receiver. The set contained four type 201 tubes, and featured a tapped loop antenna. The set had very good selectivity by virtue of having the tapped loop. By changing the taps, the set tuned different portions of the broadcast band. On one tap, it tuned 370-550 meters (545 through 810 kHz). On another tap, it tuned 224-400 meters (750 through 1340 kHz). By breaking up the tuning in this fashion, a smaller range of frequencies was tuned by the single tuning condenser, resulting in greater separation between the stations.

The article noted that during testing in Chicago, even with the Chicago stations transmitting full blast, it was possible to receive more distant stations with the speaker.

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1936: World’s Smallest Three Tube Set


Today, we offer this 80 year old miniature radio, which is barely visible.  The wearer is prolific radio writer Arthur C. Miller, who wrote the accompanying construction article.

He reported that the set, which used three miniature tubes, pulled in WCAU Philadelphia and WHAM Rochester from an office building in Midtown Manhattan. One of the tubes served as regenerative detector, with the other two serving as audio amplifier.

The antenna required some experimentation. The original idea was to wear it on the back, but the close coupling to the body meant that tuning and regeneration had to be readjusted after moving. Satisfactory results were obtained with the hat antenna, but the length required for the leadin added capacitance to the circuit, making the tuning range very narrow. He tuned the coil to 710 kHz, the frequency of WOR, and the set gave good results for WLW in Cincinnati on 700, and locals WEAF on 660 and WJZ on 760. He noted that by tapping the antenna coil, the tuning range could be increased.

1916 Boys’ Life Receiving Station


A hundred years ago this month, the December 1916 issue of Boys’ Life showed scouts how to put together this radio receiver and antenna. The author, A. Frederick Collins, explained that building the sending set might logically take precedence, but that with this set, you could listen in right away to what all of the other stations have to say. He pointed out that if you lived within a few hundred miles of any of the big government stations, you could get the correct time of day every noon, free of charge. He also pointed out that no license was required for a receiving station.

The cost of the complete receiving station was said to be about $5.

1916 Regenerative Receiver


Earlier this year, we posted a diagram of a regenerative receiver from January 1916, which was probably the first construction article detailing such a receiver. The December 1916 issue of the same magazine, Electrical Experimenter, contains this diagram of an unusual regenerative set.

This is basically two receivers, with the most expensive parts, the audion tube and variable capacitors, shared between them. Different coil arrangements could be switched into the circuit with a three pole double throw knife switch. With the switch set to the “Set A” circuit, it was a standard audion detector. With the switch flipped to the “Set B” circuit, it became a regenerative detector. Regeneration was controlled by the coupling between L2 and L1. In position A, the set could be used to receive damped waves from a spark transmitter. With it set to position B, it could be used for undamped continuous waves, and “a pure musical note may be obtained of any frequency, in the telephones.”

The accompanying article, by Samuel Curtis, Jr., first pointed out that the set could be constructed without the switch. But the circuit was designed this way because the parts were expensive.

The article noted that “the Audion bulb need not necessarily be of the most costly type, but can be any one of the tubular Audions. These bulbs give exceptional satisfaction in connection with this system, and if the experimenter should happen to be an owner of a frozen bulb, or one that will not oscillate properly, he will find that in most cases it will oscillate with this system.”

According to this site, the 1916 price of a tubular Audion was $11. As a point of comparison when looking at old prices, it’s good to remember that the cost would be 11 silver dollars, or about 11 ounces of silver. At today’s prices, this would translate to about $176. So the concept of economizing and building two receivers instead of one with the same tube doesn’t seem surprising.

Merry Christmas!


Merry Christmas from!

A hundred years ago, Santa brought this family a Victrola, the only instrument that could bring the world’s greatest artists, such as Caruso or Paderewski. The ad promised that nothing would bring so much pleasure to family and friends throughout the year. Prices ranged from $10 to $400, and dealers in every city in the world would be happy to give a demonstration.

1916companion2The ad appeared in the December 14, 1916, issue of Youth’s Companion, which also carried this ad, indicating that Santa would be giving some youngsters an introduction to wireless. This ad promised that a wireless set would keep a boy busy, and arouse the inventive scientific instinct in every red-blooded American boy. Prices for a beginner’s wireless set from the Doubleday-Hill Electric Company of Pittsburgh ranged from $10 to $50.

Caruso Cantique de Noel

Caruso’s only Christmas recording was O Holy Night (Cantique de Noel).  It was recorded on February 23, 1916, and a hundred years ago, Christmas 1916. would have been the first time it was heard.

The Loud-Speaking X-mas Tree of 1926


I’m not sure how practical the idea was, either then or now, but the December 1926 issue of Radio News offers this suggestion to turn your Christmas tree into a Loudspeaking Christmas Tree.

According to the accompanying construction article, authored by none other than publisher Hugo Gernsback himself, “a Christmas tree and music are almost synonymous.” For some years, Gernsback had been wondering why the self-evident idea of combining the tree’s scent with a radio has not been more universal.

The idea shown here killed two birds with one stone, by providing not only a base for the tree, but also make the tree musical.