The family shown here is enjoying the radio during their picnic, courtesy of a four-tube superheterodyne portable built from plans in the May 1936 issue of Popular Mechanics.
The set used a 1A6 doing double duty as oscillator and mixer, with a type 33 serving as IF amplifier, type 32 detector, and type 33 audio amplifier driving a permanent magnet speaker. The A battery was 3 volts, dropped through a resistor for the 2-volt tubes. The set also used three 45 volt B batteries in series. The result was a set that was “not only handy for beach and picnic use, but also makes a fine battery set for homes not equipped with electricity.”
The set’s chasis was mounted vertically, with the speaker mounted at one end of the case.
Here’s an idea from 75 years ago that apparently never caught on. It’s a QSL “card” in the form of a recording disc. Using a recorder such as the Wilcox-Gay Recordio, the operator would record the other station’s signal. Then, the traditional QSL data would be written in with a “special marking ink.” The blanks were from the National Recording Supply Co. of Hollywood, California. The manufacturer promised “unlimited playback with wide frequency response and a minimum of surface noise.” The blanks retailed for a dime each. This example was shown in the May 1941 issue of Radio News.
The disc is marked “Copyright Pend. National QSL Disc.” The magazine’s April 1941 issue provided more detail. It noted that “recent developments indicate that many amateurs now possess recording equipment and, instead of the old-time postcard, now use a disc to record other amateurs’ talks and send them through the mails.”
The plans for this little one-tube regenerative receiver appeared in Shortwave Craft magazine 80 years ago this month, May 1936.
It runs off household current, using a 12A7 tube, which is a dual tube containing a rectifier and pentode. The rectifier supplies the B+, and the pentode is a regenerative detector. Plug-in coils are used, for either the broadcast band or shortwave. The article recommends starting out with the standard broadcast band, where tuning is less critical. Once the operation of the set was mastered, then the builder could order a set of coils for the shortwave bands.
The filament voltage is supplied from a “curtain burner” line cord, with 350 ohms of resistance built in to drop the line voltage down to the 12 volts required by the tube. The circuit diagram is shown below. Filtering of the rectifier output is accomplished with a dual 4uF capacitor in series with a 50,000 ohm resistor. A modern recreation of this circuit would probably make use of a heftier electrolytic capacitor.
As with any AC-DC set, some caution is called for, since many of the components, and possibly the chassis, will be exposed directly to the “hot” side of the line current.
This ad for General Electric portable radios appeared in Life Magazine 75 years ago today, May 19, 1941. The main model featured, model LB-530, was a five-tube broadcast set with a tube lineup consisting of 1A7GT, 1N5GT, 1N5GT, 1H5GT, and 1Q5GT. While billed as being able to run off the internal storage battery or AC, this wasn’t entirely correct. The set always ran from the 2 volt battery, getting its 90 volt B+ from an internal vibrator power supply. The AC current would merely charge the battery, meaning that the set couldn’t really be run without a battery in place. I did have a similar model at one time, and by the time I got the radio, the lead-acid battery was long gone. The set would pull in a few strong stations without the battery in place, but the battery was an indispensable part of the circuit. The set also had provision for charging from a 6 volt car battery.
A nice example of the set can be found at this site.
The radio had a retail price of $39.95. The ad also featured other portables designed to run from dry cell B batteries, starting at $16.95.
A young man drafted into the military during World War II could give himself an edge by having a useful skill, and the June 1944 issue of Popular Mechanics reported that pre-induction code practice sessions were well attended. This created a problem, since most code practice oscillators used headphones, and acquiring enough headphones presented a logistical challenge for those running the sessions.
The solution was offered in the form of a three-tube wireless code oscillator which would transmit modulated CW to a nearby broadcast receiver, producing room-filling volume. In light of wartime parts shortages, the circuit called for common receiver tubes which could probably be scavenged from another set. The plans called for a 6C5 rectifier, witn 6J5’s serving as AF and RF oscillators. The 6 volt filament voltage was obtained by wiring a 40 watt lightbulb in series with the filaments. The completed circuit is shown here mounted on a circular cutting board. The output of the oscillator was run to the receiver’s antenna jack, or simply placed near the set’s antenna.
Pictured here in the May 1936 issue of Radio News is Helen Marshall, one of the three named “Miss Radio of 1936” by radio pioneer Nils T. Granlund, the other two being Dorothy Lamour and Harriet Hilliard (later known as Harriet Nelson of Ozzie & Harriet fame), also of NBC.
She was the leading soprano of Sigmund Ramberg’s Studio Party, heard Tuesday nights on NBC.
Yesterday, we showed the mysterious circuit here, from the May 1956 issue of QST. The two boxes are connected by only two wires. Yet switch #1 controls lamp #1, and switch #2 controls lamp #2.
And this was 1956, so there’s not a Raspberry Pi inside each box sending control signals back and forth. As you probably figured out, the trick involves four diodes. If one had examined the circuit in action, they might have noticed that the bulbs weren’t burning at quite their full intensity. But according to the solution in the June issue, the effect wasn’t great enough for most people to notice. Here’s the complete circuit:
When one switch is turned on, it sends positive pulsating DC, which can only pass through one of the diodes. When the other switch is turned on, it passes negative pulses, which can only pass through the other diode. When both switches are turned on, the AC is more or less unaffected, and both lamps light.
This 1956 version used selenium rectifiers. The modern version could use silicon diodes, and fit inside a much smaller package.
In the 1940’s and 1950’s, QST occasionally ran a feature called the “Quist Quiz.” This one appeared sixty years ago, in March 1956. It’s not quite as difficult as the last one we shared, and I promise you won’t need to use the quadratic equation to solve it.
The problem consists of two small metal boxes, shown here. The one on the left contains an AC line cord and two switches. The one on the right contains two small lamps. Running between them are two wires. (The accompanying text points out that there are no hidden conductors–only two conductors run between the boxes.)
When one switch is flipped, one lamp lights. When the other switch is flipped, the second lamp lights. When both switches are turned on, both lamps are illuminated. Can you figure out the circuits inside the two boxes? The answer will appear tomorrow.
According to QST, the two boxes were the creation of Dr. Earl Weston, W8BXO, who passed away in 2009 at the age of 97.
This is either a great idea, or a really bad idea. Whichever it was, it appeared in the 1956 Allied Radio catalog. The idea was simplicity itself, as revealed by the diagram. One man can put up an antenna and a 73 foot tower without ever leaving the ground. “Just bolt the sections together and easily push up bottom half. Then turn the crank and up goes the second half!” The bottom half was steel, and the top half was aluminum. What could possibly go wrong?
Sixty years later, these don’t seem to be available, and even though I’m not a mechanical engineer, I think I can see a couple of reasons why. First of all, I bet the top section needs a little nudge from a second man on the ground to start cranking from that insanely acute angle, but that’s not an insurmountable problem. I would definitely want to be wearing a hardhat when the top section travels the last couple of inches, since it seems to me that it’s going to drop into place by gravity without any control from the crank. And during the time that the top half is sticking out perpendicular, I would think that it really needs to be firmly tied down on the other side, to keep the whole thing from tipping over.
The biggest problem I see is that the cable is a permanent structural part of the tower. If the cable breaks, or even if some curious passerby wonders what happens when the crank is turned, nothing is holding up the tower other than gravity and the guy wires.
The description says that it will withstand 90 MPH winds. But I wouldn’t want to be standing anywhere near it when those winds were blowing.
Of course, maybe I’m wrong about those things. If so, then this is a great idea.
Shown here under the sheets is Brigitte Bardot from the 1959 French comedy Babette Goes to War (Babette s’en va-t-en guerre). Of particular interest to our readers is, of course, what she’s doing under the sheets, namely, sending CW. Babette, a French country girl in London, played by Mlle. Bardot, does her part in the war effort by parachuting into German-occupied France to kidnap a German general. She bumbles through her mission with a heroic finish.
In this still from the movie, the naysayer might point out that her technique with the key leaves something to be desired. However, the criticism is unwarranted given the circumstances. She is transmitting from underneath her sheets in the very hotel that was serving as the Nazi headquarters. The German direction-finding truck pinpoints her location, a Nazi bursts into her room, only to retreat when the girl under the sheets protests that she’s naked.
The film was a big hit in France, with over 4.6 million tickets sold. On this side of the Atlantic, the New York Times review proclaimed the film to have “the anomalous distinction of being occasionally farcical and somewhat incomprehensible.” The review lamented that “Bardot is clothed almost as abundantly as an Eskimo most of the way through this World War II spoof, and a fully dressed Mlle. Bardot is downright confusing.”
The movie’s trailer, which includes the exciting scene of Mlle. Bardot being tracked by the Nazi DF’ers, in shown here:
This clip shows her send and receive the complete message;
https://www.youtube.com/watch?v=k6HDBMtshZ0
She sends mostly V’s, and a few other random characters which, according to the CW to French subtitles, mean “ALLO LONDRES – LE LEOPARD EST DAN LA CAGE AUX MOUCHES – STOP – C’EST DU PEU AU JUS – FAITES CHAUFFER LA COLLE.” She gets the message back from London, which sounds like “OK OK” to me, but according to the subtitles means “COMPRIS – TRES BIEN – MESSAGE TERMINE.”
The movie doesn’t appear to be available in North America, but you can get a PAL version at Amazon.
