Monthly Archives: April 2017

1937 Popular Mechanics 40 Meter Transmitter

1937AprPMXMTREighty years ago this month, the April 1937 issue of Popular Mechanics carried the plans for this simple 40 meter transmitter employing a single 6L6 tube. The set used an 80 meter crystal, and according to the article, using the crystal on its second harmonic resulted in particularly good keying.

The set called for a power supply delivering 400 volts at about 100 milliamps.

It was said to have a range of about 500 miles.

1932 Lens Disk Television

1932MarAprTV85 years ago this month, the televisionist shown on the cover of the March-April 1932 issue of Television News is working on a rather ambitious project.  He’s graduated from the tiny peep-hole sets to a larger set capable of displaying an image of 10-12 inches.

The secret to this ambitious design is the fact that it incorporates 60 matched lenses in the spinning disk itself, rather than merely relying on small holes cut into the disk.

American Radio 1942: WGAC, Augusta, GA


Seventy-five years ago, this day’s issue of Life Magazine, April 27, 1942, carried a photo essay about American radio as it went to war.  The article claimed that war marked the end of a “rich era” which brought fresh problems to the medium. It predicted, with little supporting evidence, that declining advertising revenues were on the way. It asserted that “war has thrown new problems at radio–of presenting fact and propaganda, of keeping commercialism and patriotism decently separated, of informing and stimulating the public.” It acknowledged a few bright points, such as the program “This Is War,” whose production is shown above.

It carried summaries of the current offerings, such as comedy, soap operas, and music, and asserted that programming often catered to the lowest common denominator.

WGAC studio and transmitter.

WGAC studio and transmitter.

The most enlightening part of the feature was the magazine’s look at what it viewed as a typical small station, WGAC, Augusta, Georgia, which then ran 250 watts from 6:30 AM to Midnight.  It carried the NBC Blue network, and had a range of about 60 miles day, 15 miles night.

The station is currently licensed to  Beasley Broadcast Group, Inc. and broadcasts on 580 kHz, 5000 watts daytime, 840 watts nighttime.


WGAC broadcast of service of St. Paul’s Church.

WGAC commentator and Augusta Herald editor Sam Moss.

WGAC commentator and Augusta Herald editor Sam Moss.

Thomson, GA, high school girls Barbara Burch, Lucy Lockett, and Winona Colton, WGAC's star trio.  "They sing in close harmony just like the big-time girl trios."

Thomson, GA, high school girls Barbara Burch, Lucy Lockett, and Winona Colton, WGAC’s star trio. “They sing in close harmony just like the big-time girl trios.”

KSTP Morse Code Lessons, 1942

1942April27BCOn this day 75 years ago, April 26, 1942, KSTP radio in St. Paul, MN, began an innovative program, as described in the article shown here from the April 27, 1942, issue of Broadcasting.

According to the report, the station was doing its part to help satisfy the great demand by the armed forces for radio operators, by conducting weekly programs designed to teach young men and women the international Morse code.

The weekly program aired Sundays at 9:30 AM, and “used drama, as sugar-coating for the lessons.” It was built around a small family, one of whom was an amateur operator. Script writing was done by Jack Hill of the St. Paul Radio Club, using lessons from the American Radio Relay League.

After the third week’s episode, the station planned to incorporate “teaser announcements” into the program in an effort to determine how many would be interested in lessons one night a week in classrooms in Minneapolis and St. Paul. The St. Paul Radio Club would furnish instructors for those courses.

The program seems to have been a great success, as reported in the September 1942 issue of QST (pp. 80-81). The fifteen minute weekly programs resulted in a total of 325 Twin City residents signing up for the classes, initially held at KSTP’s Minneapolis and St. Paul studios, with advanced students moving on to classes at the YMCA.

According to QST, transcripts of the radio broadcasts, featuring the “Strong” family, were available by mail by writing to Hill at 1138 Fauquier Avenue (now known as Bush Avenue) in St. Paul.

1937 5 Meter Transmitter

1937AprRadioNewsShown here on the cover of the April 1937 issue of Radio News is E.M. Walker, W2MW, at the mike of his 5 meter transmitter, the construction details of which are found in the magazine. The set was billed as ideal for the ham who couldn’t afford a crystal controlled rig for the super highs, since he reported many reports of the signal being comparable to crystal control. The transmitter itself for CW consisted of two 6L6 tubes. The accompanying modulator used four tubes, two push-pull 6L6’s along with a 6F6 and 6CF serving as audio preamplifiers.

The transmitter was very compact, with the RF portion and modulator each mounted in 14x7x8 cabinets.

The author stressed the importance of care in winding the oscillator coils, and noted that some experimentation might be necessary to get them right on frequency.

Schematics of RF section (left) and modulator (right).

Schematics of RF section (left) and modulator (right).

1867 Manhattan, KS, Earthquake

On this date 150 years ago, April 24, 1867, Kansas experienced its largest ever earthquake, with its epicenter just north of Manhattan, Kansas.  It was felt over an area of almost 200,000 square miles, and caused minor damage in Kansas, Iowa, and Missouri, along with a handful of injuries.  Damage included cracked plaster, downed chimneys, and loosened stones in buildings.  At Paola, KS, one wall of the post office was destroyed.

The report shown here appeared in the Chicago Tribune on April 27, and originally appeared in the St. Joseph, MO, paper on April 25.  In St. Joseph, the earthquake was described as a “low rumbling sound, similar to that produced by a heavily loaded wagon passing over a bridge.”  At St. Joseph, “almost the entire population had rushed terrified from counting rooms, workshops and kitchens into the streets.  At first everybody seemed to be under the impression that his particular building had suddenly become possessed of an unusual number of devils, and was pirouetting by itself; but upon seeing his neighbors rushing out under apparently the same conviction, the idea flashed upon him that an earthquake had playfully jousted us.”

1947 FM Converter

1947AprPMFMconvPrior to World War II, the relatively new FM broadcast band was located at 42-49 MHz. After the war, it moved to its current home at 88-108 MHz. This false start was one of the reasons why FM took years to catch on: The early adopters owned receivers which were now useless, since the stations had all moved.

One solution was building a converter, and a number of designs were available. One of the simplest is shown here, and appeared in the April 1947 issue of Popular Mechanics.

The circuit originated with Henry R. Kaiser, the chief engineer of FM station WMOT in Pittsburgh. When WMOT changed frequencies, there were about 6000 obsolete receivers in the area which could no longer hear the station.

Kaiser originally designed a circuit with a crystal oscillator, and a 1N34 diode as mixer. During experiments, the tube oscillator failed. Much to his surprise, the circuit converted the frequency of another FM station. With a bit of tweaking, he came up with this circuit which put his station on the old receiver’s dial without any power.

The article doesn’t explain how the circuit works, probably because the author didn’t know. But at least for a strong signal, the circuit did work, and could be used to put some of those obsolete sets back in service.


75th Anniversary of End of Civilian Radio Production


As we previously reported, on this date 75 years ago, April 22, 1942, the last civilian radio receivers rolled off the assembly lines.  For the duration of the war, no more radios or phonographs would be produced, the nation’s industrial output instead being devoted to the war effort.

The photo here shows one of the last RCA radios to be produced before the deadline.  This ad, which appeared in the May 1942 issue of Radio Retailing, shows RCA Victrola No. 17,199,547, which was the last set to be produced at RCA’s Camden plant, on April 7, 1942.

With no more new sets available, the nation’s radio servicemen were acutely aware that they would bear the full responsibility of keeping the nation informed and entertained by keeping existing sets running.


1942 Aircraft Detector


Seventy-five years ago this month, the April 1942 issue of Radio Craft showed the defense-minded electronics hobbyist or serviceman how to put together this aircraft detector. According to the magazine, the detector would be of particular interest to civilian defense units around the country. Cost of parts was set at $50, and the detector used readily available parts. In tests, it was able to pick up conversations at three blocks, and the sound of a bomber ten miles away.

Detail of horn-microphone assembly.

Detail of horn-microphone assembly.

The “ear” consisted of an old phonograph horn with a sensitive microphone mounted at the base. The four-tube battery operated amplifier employed three 1H5GT and one 1G4G tubes and allowed the operator to scan the skies for approaching planes with headphones.


1942 Midget 3 Tube TRF

1942AprPS11942AprPS2Seventy-five years ago this month, the April 1942 issue of Popular Science showed how to put together this midget 3-tube broadcast receiver. The set was said to provide loudspeaker volume for stations up to fifty miles away. Thanks to the miniature tubes employed, the set could fit into a woman’s handbag.

The set used a type 9003 pentode as RF amplifier, with a type 9002 triode serving as detector. A 70L7GT dual tube served as audio amplifier and rectifier. The filaments were wired in series, with a 200 ohm line cord dropping the voltage.

For an antenna, the article recommended about 15 feet of stranded wire lying on the floor.