Monthly Archives: March 2017

Preparing for the End of Civilian Radio Production

1942MarService

By orders of the War Production Board, manufacturing of civilian radio receivers ended on April 22, 1942, for the duration of the war. Even before this was announced on March 7, radio servicemen knew that at the very least, there would be shortages. When the ban was announced, they knew it was up to them to keep America’s radios in operation for their vital war information and for morale.

When the ban was announced, servicemen knew that it was time to double down, and they were reminded by advertisements such as this one, which appeared in the March 1942 issue of Service magazine.  The ad was from the John F. Rider company, publisher of service manuals.  These manuals contained diagrams and service information of virtually every set ever manufactured, and this data would prove invaluable for the radio servicemen tasked with keeping the nation’s radios in operation for the duration.



1967 One Tube CW Transmitter

1967MarEI

Fifty years ago, the March 1967 issue of Electronics Illustrated carried the plans for this simple 40 meter CW transmitter. The set ran directly off AC power, with a transformer supplying 120 volts B+, rectified through two silicon diodes, as well as 6 volts for the filament of the single 6AQ5A tube. It ran 15 watts input power, with output of about six watts.

The author, James B. White, W5LET, noted that the transmitter would be a good first rig for the Novice, as a perfect second rig for the oldtimer, or tucked away on the corner of the operating table for use as a standby transmitter.

The parts count was kept down by omitting a variable capacitor for tuning the plate circuit to resonance. Instead, the tube’s plate-to-cathode capacitance was tuned against the plate coil, which was adjusted with a slug-tuned core. A neon lamp was used as the RF indicator to assist with the tuning process and to visually monitor sending.

The rig got out, and the author reported that his first CQ from Louisiana was answered immediately from the Midwest. During its first hour on the air, the author worked both coasts.

1967MarEISchematic



1967 Outlet Tester

If you do any electrical work around the house, or even if you don’t, and you want to make sure the electrician did things right, you really ought to have an inexpensive outlet tester like the ones shown here. You’ll be able to tell at a glance whether the outlet is wired correctly, or if there’s some invisible fault. Those errors could include the polarity being reversed, either the neutral or the hot not being hooked up, or the absence of a ground connection. The one shown here is available on Amazon, and they can be had at low cost at any hardware store.

But fifty years ago, they weren’t so readily available, and the home handyman might consider making his own. The plans were shown in the March 1967 issue of Popular Mechanics. As you can see, the device is quite simple. If you want to make your own, here’s the schematic:

1967MarPM



Fire Island Light Ship Distance Measuring Apparatus

FireIslandLightShip

A hundred years ago this month, the March 1917 issue of the Wireless Age carried a description of the distance measuring apparatus in use by the Fire Island Light Ship,  The light vessel, located in New York Harbor, was equipped with apparatus which would allow an approaching ship to accurately measure its distance from the station.

To do this, the light vessel used a radio transmitter (call sign NLS) and a 1000 pound submarine bell. The bell would strike a sequence. At a precise time after the first strike of the bell, the radio would send a series of dots. An approaching ship would hear the bell, followed by the radio signal. The difference in time between these signals would correspond to the distance travelled by the two signals.

The announcement explained that the best way to copy the signal would be with headphones connected so that the wireless signal was played in one ear, with the other receiver connected to the submarine bell detector.  It would then be an easy matter to distinguish the signals.  Since the dots coming from the radio transmitter followed a carefully controlled pattern, it was necessary only to count the dots heard prior to hearing the bell.

The radio operated on a wavelength of 600 meters (500 kHz), and ran continuously during thick weather, and during the first 15 minutes of the hour during clear weather.

The vessel, Lightship LV-68, was built in 1897 at a cost of almost $75,000, and had a length of 122 feet. Each of its masts held a 100 candlepower electric lamp. It also carried a 12 inch steam whistle in addition to the bell.  It remained in operation until 1930.

References



1957 Combination Radio-Geiger Counter

1957MarPMGeiger

Sixty years ago, prospecting for uranium was a popular pastime, and the gentleman shown here in the March 1957 issue of Popular Mechanics was doing it right. The accompanying article noted that prospecting could be a lonely proposition, and this project allowed you to bring along a companion who would assist and entertain you without demanding a portion of your claim: You could build this combination radio-Geiger counter!

The basic circuit was a superheterodyne radio, using four tubes: 1R5, 1U4, 1U5, and 3V4. The Geiger counter used a 1B85 Geiger tube from the Victoreen Instrument Company. The filaments ran off two cells, and a 45 volt battery supplied the B+. Since 45 volts wasn’t quite enough for the Geiger tube, the circuit used an transformer and spark-gap circuit to charge up a capacitor to a higher voltage. The is was accomplished with a pushbutton in series with the transformer’s primary. You would pump the pushbutton for about 30 seconds to charge the capacitor, which would allow a sufficiently high voltage for the Geiger tube.

The output of the geiger counter went to the audio section of the radio, and when you hit uranium, you would hear the clicks from the speaker.

In the diagram below, the radio is shown in black and Geiger counter in red.  The magazine also noted that if you already had a suitable portable radio, you could add the Geiger counter circuit.

1957MarPMGeigerSchematic

 



Carbon Button Microphone Amplifier

CarbonMicrophoneAmp

While they were rarely used in radio applications, the diagram here shows how a carbon button microphone amplifier could be used to drive a loudspeaker from a crystal set. This diagram is from 90 years ago, and appeared in the 1927 British Radio Year-Book.  The diagram actually appears in the advertisement for a book entitled Successful Crystal and One Valve Circuits by J.H. Watkins, who according to the ad was the wireless correspondent for the Daily Express.

The principle behind the circuit is very simple and almost self-explanatory.  The audio from the crystal set or other low-level source is fed to the traditional earphone.  A carbon button microphone is in physical contact with the earphone, and produces a stronger AF signal.  In this case, this stage is able to drive a loudspeaker.

This idea was rarely used in radio, since a vacuum tube amplifier provided better results and little additional cost.  The carbon button amplifier was more commonly used in telephone circuits, where they were the only method of amplification available prior to the vacuum tube.  They made long distance telephony possible.  They did have the advantage of a smaller size than a vacuum tube, and required less battery power.  Therefore, they did remain in use in hearing aids until the advent of the transistor three decades later.  You can read more about the carbon button amplifier at this site.

The advantage for the home constructor was probably cost, since driving a speaker this way would not require an expensive vacuum tube.  In fact, the carbon button amplifier could probably be constructed at home, which would be impossible in the case of a vacuum tube.  Students looking for a very novel science fair project might consider making one, since it would be possible to produce loudspeaker volume with entirely homemade components.



Highland Park College, Des Moines, IA

1917MarElecExp

A hundred years ago, magazines devoted to electricity or mechanics were full of ads for learning radio.  A large number of these focused on training ship wireless operators.  There were other exceptions, but most such schools were located near the sea, in locations such as New York.

One of the exceptions that caught my eye was this ad for the “very thoro” wireless training program offered by Highland Park College in Des Moines, Iowa, shown here as it appeared in the March 1917 issue of Electrical Experimenter.

The ad promised the opportunity to see the world and draw a big salary as a wireless operator.  And the first stop in seeing the world was Des Moines.  This is actually not surprising, since the Hawkeye State was a hotbed of early wireless activity, with more than its fair share of amateur operators, and later, broadcast stations and companies involved in radio.

The college offering this course, Highland Park College, is no longer in existence, but had its own colorful history.  The school’s Wireless Building, apparently the location where students would be trained to see the world, is pictured here in the school’s 1914 yearbook.

According to the yearbook, the college had a wireless club which had been organized in April 1913, and had a complete sending and receiving set. The book boasted that the station’s large aerial allowed reception of the Arlington, VA, and Key West, FL, stations on a regular basis.

HighlandParkWirelessBuilding

The college was established in 1889 and operated under that name until 1918.  It was apparently independent when founded, and in 1911 was transferred to the Presbyterian church.

1915MarPMWireless telegraphy was only one trade that could be acquired at Highland Park College, as shown by this ad in the March 1915 issue of Popular Mechanics.  The school also offered courses in machinist, automobile machinist, and chauffeur.  The machinist courses ran 48 weeks, whereas the chauffeur course of study could be completed in 12 weeks.  The school also offered a “special 6 weeks driving course.”

In 1918, the college was acquired by the Baptist church and renamed Des Moines University. Things went smoothly until 1927 when a fundamentalist wing known as the Baptist Bible Union of North America, the forerunner of the General Association of Regular Baptist Churches, took control. The faculty were required to subscribe to eighteen articles of faith. At that time, the University’s school of pharmacy was apparently the strongest department, and the faculty apparently had doctrinal differences to the point where they refused to sign the eighteen articles of faith. They departed and formed the Des Moines College of Pharmacy in downtown Des Moines. All but two of the pharmacy students left to enroll in the new school.

In addition to the doctrinal requirements imposed on the faculty, the students were facing restrictions. Three girls were disciplined for doing cartwheels during a vaudeville skit.

By 1929, the administration had enough, and fired the entire faculty. A riot broke out, and angry students stormed the administration building during a meeting of the board of trustees. Eggs and rocks were thrown, and the angry students attempted to break down the door of the room where the board members were hiding. Police were called, but the school formally closed down in September 1929.

The buildings sat vacant until 1943, when professional baseball player and aviation pioneer Alfred W. Lawson bought the property and founded the Des Moines University of Lawsonomy, Lawsonomy being billed as “the study of everything.” As might be expected for the study of everything, a degree was not something that could be earned quickly. According to Lawson, the students (men only) would need to study for 30 years to get their degree of Knowledgian.”

Enrollment peaked at a hundred students, but dwindled to 20 when the school closed in 1954 (presumably, with none of the students earning the coveted Knowledgian degree).

The property was sold, two weeks before Lawson’s death, and became the site of the Park Fair Shopping Mall.

Highland Park College in 1914. Library of Congress.

Highland Park College in 1914. Library of Congress.

ParkFairStreetView

The school’s location today. Google Maps.

References



1947 “Little Giant” All American Five

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For many years, the March issue of Popular Mechanics had the tradition of carrying the plans for a radio receiver billed the “Little Giant.” A few weeks ago, we featured the 1942 version, and today we offer the version shown 70 years ago in the March 1947 issue.

1917MarPMLittleGiantSchematicThe circuit diagram for the 1947 version will look very familiar with those who’ve dug into postwar AM radios, since it’s the classic “All American Five” circuit employed for many years by most radio manufacturers. This one has the familiar complement of octal tubes: 12SA7GT, 12SK7GT, 12SQ7GT, 50L6GT, and 35Z5GT. This is also known as an “AC/DC” set, since it could run off either AC or DC 115 volt household current. It’s transformerless, since it rectifies the line cord for the B+ voltage, and wires all of the filaments in series to run directly off the line current.

This circuit does have one interesting postwar twist. Variable condensers were still in short supply, so it uses permeability tuning. Instead of a variable condenser and fixed coil, it uses a fixed condenser and variable coil. The inductance is varied by moving a plastic molded iron core in and out of the coils.



Old Glory: Banned in Boston

1917MarchElecExp

We recently carried an image , a smaller version of which is shown at the right above, of the SS Kansan, illustrating how the U.S. flag was illuminated to make abundantly clear that the ship was a neutral vessel.  The image appeared on the cover of the January 1917 issue of Electrical Experimenter.

Newsstand readers in Boston, however, didn’t see the flag.  Instead, some of them saw a sticker of Santa Claus.  Massachusetts law forbade the sale of goods displaying the flag, so news dealers were forced to obscure it.  In this case, Santa Claus got the honors of being the censor.  The image above is taken from the magazine’s March issue, which explained the odd juxtaposition.

1937 Armchair Radio

1937MarPS

Eighty years ago this month, the March 1937 issue of Popular Science showed how to put together this receiver, which undoubtedly provided armchair copy of local broadcast stations. The author, Clark Maxwell, (not to be confused with James Clerk Maxwell of Maxwell’s Equations fame) explained that he had tried for several years to find a convenient but inconspicuous place for the radio in his living room. He decided to solve the problem once and for all by designing this set to hang on the arm of his favorite reading chair.

He billed the set as the “Arm-Chair Five,” due to the fact that it had five tubes inside. The radio itself consisted of three tubes, since one served as the rectifier. The fifth “tube” was actually a ballast to drop the voltage of the filament chain.

The circuit was a TRF, with one 6K7 serving as RF amplifier. A 6J7 and 25A6 served as audio amplifiers to drive a speaker.

The author used the set with a 25 foot indoor antenna, although he noted that an outdoor antenna could be used.

Since the chassis was “hot,” he stressed that under no circumstances should an external ground be used. The set was encased in a wooden box covered with fabric to match the chair.

1937MarPSschematic