Category Archives: Radio history

1950 Five Tube Superhet

These lucky youngsters have probably been drawing Social Security for about a decade, but in 1950, they were tuning in a favorite program on this attractive five-tube radio put together by their dad and big brother. The internal circuitry was a typical “All American Five” superhet, with a tube lineup of 12SA7, 12SK7, 12SQ7, 50L6, and 35Z5 rectifier. Since this was an AC-DC set, the article cautioned that the screws holding the chassis to the wooden case should be covered up for safety.

The cabinet is designed to resemble a circus wagon. The front is carefully painted with red and white enamel paint, with wooden dowels making the cage. Then, after the paint has dried, animal decals are applied.

The plans appeared in the August 1950 issue of Popular Mechanics.

1960 Loudspeaker Crystal Set

Sixty years ago this month, the August 1960 issue of Popular Electronics showed how to make the holy grail of crystal sets: a crystal set capable of loudspeaker operation.

The author, Walter B. Ford, reported good reception, including loudspeaker volume on strong local stations. The set relied upon two secrets. First of all, it had two tuned circuits in the front end for maximum selectivity. It also used two 1N34A diodes in a voltage-doubling circuit. For weaker stations, headphones could be used, or it could be used as an excellent AM tuner for an external amplifier. But for the strong stations, it would drive the speaker, with no power source other than the received signal.

The ferrite loopsticks might be hard to find these days, although with a ferrite rod, you should be able to make your own. More information can be found at this link. More hints on sourcing the parts can be found at my crystal set parts page.

Light Bulbs as Dropping Resistors

This photo isn’t as sinister as it looks, and nothing untoward is going to happen to the gentleman at the left. The photo is from the August 1945 issue of Popular Mechanics, and these gentlemen are dealing with wartime parts shortages. They’re doing an emergency repair on this set, and need some way to power the filaments of the six-volt tubes. The filament transformer they need is a wartime priority item, so they instead wired the filaments in series and used a 40-watt light bulb as a dropping resistor.

The picture is accompanied by a table showing the resistance of common lamps.

1970 Multiband Mobile Antenna

This month marks the 50th birthday of a pretty good idea, as evidenced by the cover story in the August 1970 issue of Popular Electronics. The article was penned by Russ Alexander, W6IEL, who was likely the originator. The article specifically addresses how to use a compact antenna from an apartment, and it makes use of Hustler mobile antennas.

The Hustler antenna is still available today, in more or less identical form. It amounts to a center loaded vertical antenna. The bottom half is a mast that attaches to the car. On top of that is a loading coil, and on top of that is a whip antenna. The loading coil and whip are tuned to a specific band. And because you need different coils and whips for different bands, the coil and whip are sold as a one-piece resonator.

So it’s fairly easy to change bands: You stop the car, get out, and swap out the resonator. But that doesn’t work very well if the antenna is mounted on the roof of your apartment building. And it doesn’t work very well if you want to change bands without getting out of the car.

So the author went to his metal shop, and made a piece which allowed him to mount up to four resonators on the same mast. For bands that are not being used, the coil acts as a trap, so the unused resonators have little impact on the transmitted signal.

The idea caught on. I first remember seeing one of these as a young ham in the 1970s in the parking lot at a hamfest on the car of prominent Minnesota ham Tod Olson, K0TO (then W0IYP). I remember thinking that it was a pretty good idea. Chances are, it originated with the magazine article shown here.

Shown in these pictures is the mobile antenna of W6LEN, an avid WWFF activator of Southern California parks and beaches. He uses the Hustler mobile antenna on a magnetic mount on top of his minivan. While the magnetic mount is probably too small to use in motion, he has had good success with this antenna, and it takes only a few minutes to deploy when he arrives at his destination. As with the 1970 article, he uses a homemade bracket to mount the four resonators.

Hustler eventually realized that using multiple resonators was a good idea, and they now sell the part, shown at right, so you don’t have to have your own metalworking tools. The author of the 1970 article recommended having the part plated with copper and then cadmium, after which “the finished bracket will look like a commercially marketed item.” The 1970 Popular Electronics version had room for four resonators, whereas the commercial product has only three wings. However, a fourth resonator can be added in the middle.

Expedient Variable Resistor

I’m not sure it would comply with modern OSHA rules, so whatever you do, make sure you don’t touch any of the exposed conductors. But if you need to quickly come up with a low voltage, this self-explanatory method of making your own resistor should do the trick. Measure the voltage, and keep adding salt until you get the desired voltage.

The idea appeared in the August 1945 issue of Radio Craft. It had been sent in to the magazine by one Ollie Peoples of Mountain View, Oklahoma, who pointed out that if you can’t reach the desired voltage, then use a larger glass and add more salt. He reported that the average glass wouldn’t deliver more than six volts, and would get unduly hot with that voltage.

As long as they’re careful with the high voltages involved, advanced students could use this idea as part of an interesting science fair project, demonstrating how changes in salinity affect the resistance.

WW2 Music at Work

This image could be mistaken for the studio of a small radio station, but it’s actual the public address console of a wartime industrial plant. Specifically, it’s the console of the RCA Plant Broadcasting System. It appeared in the August 1945 issue of Radio Service Dealer, as part of an article penned by the manager of RCA’s Music Library Service. The article is one of a series giving dealers ideas on how to promote the P-A business, and focused on providing music in the industrial environment.

Plant managers learned that by piping in the right mix of music, they would increase productivity and worker morale. Such sound systems were suitable for industrial plants, as well as office areas devoted to stenographic and clerical work. Business offices such as banks and insurance companies could play music both for workers and customers. And in hospitals, hotels, and stores, music could be piped in over sound systems.

RCA had the musical programming down to a science, and had packages of records available for sale to companies. Musical selections were broken down into four categories.

First of all, there was music for the opening period. These songs would play as workers arrived, and would continue for about fifteen minutes after starting time. These were invariably marches or patriotic tunes, such as “Stars and Stripes Forever,” or the “Washington Post March.” Other possibilities would be upbeat or fast tempo dance selections such as “Pennsylvania Polka.”

About an hour and a half after starting time, and again about an hour and a half before lunch, songs from the “Fatigue” playlist would be played. More songs from this list would be played similar times in the afternoon. Many of these were waltzes, and also popular hits, Latin and Hawaiian tunes, or old time favorites. Some songs on this list included “Green Eyes,” “Star Dust,” and “Begin the Beguine.”

The magazine stressed that the playlists had to be fine tuned to the audience. For example, it noted one small plant where about 75% of the workers were girls between 18 and 23. The music picked for that audience simply wouldn’t work at a plant where most workers were over 35.

RCA’s library also included some records for special occasions, such as Christmas songs and more patriotic tunes.

Workers at Davis & Geck, Inc., Brooklyn, N.Y., pack surgical sutures with the help of music piped in from wall-mounted RCA speakers.

One office employed 600 girls doing monotonous filing duties. Normally, at about 3:00, fatigue would set in, but the author observed those 600 girls instead singing along softly with a popular recording. The office manager was initially skeptical, but experience showed that the vocals did not impede efficiency.

A plant with many Polish or Slavic workers would get more polkas and folk dances. One plant in Trenton employed mostly Italians, and that plant had almost every record Caruso ever made.

Toward this end, one service featured by RCA was a survey that could be given to workers and analyzed at headquarters in Camden, N.J. to come up with a custom record library from the RCA catalog. “The psychological effect of having the personnel feel that the music is theirs, played for them, gives them a personal interest in the project which is otherwise unattainable.” The overall effect was greater efficiency, less absenteeism, and better output.

On the other side of the Atlantic, Britain was also seeing to it that war workers had music. The BBC program Music While You Work was programmed following similar principles. One interesting rule for the BBC program was the banning of the song “Deep in the Heart of Texas,” due to the potential danger of workers taking their hands off their work to perform the hand claps in the chorus.

Electronics Illustrated

Just over fifty years ago, I was carefully perusing the letter addressed to my dad from Publisher’s Clearing House. The head honcho of that firm was Robert H. Treller, and he always took a personal interest in our family, since the letters were always full of personal handwritten notes directed to us.

Image, Twitter @harrymccracken.

Robert H. Treller was always eager to make sure we qualified for the big prize drawing, although we never got picked. I remember that one of the letters had testimonials from previous winners, one of whom happened to be in our local calling area. I still remember that they were in St. Paul Park, Minnesota. Just to make sure that Robert H. Treller was on the level, I actually called them to inquire whether they had really won the prize. Sure enough, the woman who answered the phone cheerfully assured me that Publishers Clearing House was legit.

Of course, Robert H. Treller wasn’t in the business of just handing out money, although that was a big part of it. He had magazines that had to be cleared out of the house at steep discounts. The envelope contained a sheet of stickers for the magazines, and you returned the ones you wanted to subscribe to. No money changed hands–they cheerfully billed you later.

Among the magazines with a sticker was one with the intriguing title of “Electronics Illustrated.” I don’t remember the price for a year’s subscription, but I’m sure it was close to zero. I affixed the sticker to the entry form and sent it in. And four to six weeks later, I received the issue shown above.

None of the projects in that issue jumped out at me as something that I wanted, but I do remember reading about DX’ing the Indian Ocean and the Phillipines. Also, I remember the Lafayette CB radios looked very intriguing, although way out of my price range. The stereo pictured on the cover was the Toshiba KS-1810H. But since I never did win a prize from the Publishers Clearing House, it was also well out of my price range at $99.95.

Home AM Broadcasting: 1960 and 2020

Sixty years ago this month, the August 1960 issue of Popular Electronics was a particularly good one. In an upcoming post, we’ll feature one of its construction articles, the elusive loudspeaker crystal set. There’s also a primer on soldering, and a guide to restoring shortwave receivers from the 30s and 40s and turning them into state-of-the-art communications receivers. There’s even the obligatory one-tube radio, namely a one-tube superregenerative receiver for the FM broadcast band.

The issue also showed the ambitious cover project, a portable oscilloscope. These days, of course, you can get a much better one at a much lower price, such as the one shown at left, conveniently available on Amazon.

And one particularly intriguing teaser on the cover promises to tell you all about unlicensed two way radio. The magazine was pointing to FCC rules that are still in effect today in more or less the same form, namely Part 15. Among other things, they allow license-free broadcasting on the AM broadcast band, as long as the transmitter input power is less than 100 milliwatts and the antenna is less than 10 feet long (today, strictly speaking, the allowable antenna is now two inches shorter, because the limit is now 3 meters). Of course, you also need to avoid interference with licensed stations. The magazine explained how you could use two transmitters, along with two broadcast receivers, for a two-way operation. It gave other ideas on how to use such a transmitter, such as mounting it in a car, to stay in touch with another car that’s driving with you, or even to talk to the house while driving by.

Back in the day, as the source of your transmitter, the magazine recommended a wireless phono oscillator. We’ve discussed these before, and they were readily available, either assembled or in kit form, to listen to a phonograph on a nearby radio. These units usually had a range of 50-100 feet. But with the full-size (10 foot) antenna carefully placed, the range could be much greater. According to the magazine, the signal could be picked up by a good car radio a half mile away.

Due to COVID-19, home broadcasting is making a comeback. In particular, there are many applications where you might want to broadcast to nearby car radios. A church, for example, can have its service in the parking lot, with churchgoers listening on the car radio. They can see the altar, but they’re safely distanced in their car. Along with an inexpensive video projector, neighbors can come together for an impromptu drive-in movie.

Review of the Talking House AM Transmitter

Of course, there’s no such thing as a phono oscillator any more, so where do you get a good transmitter? The answer is the transmitter shown at the left, the reasonably priced InfOspot Talking House transmitter. I recently bought one, and I am absolutely amazed at how well it works.

The name derives from the fact that it was originally marketed to real estate agents. The agent would record a short sales pitch for the house, put a sign outside inviting passers by to tune in to a particular spot on the dial, and the house would literally start selling itself.

Because this is the intended use, the Talking House has a built-in digital recorder. You can record a continuous loop of up to about five minutes. Earlier models of the Talking House were capable of only the continuous loop–you couldn’t broadcast live with them. Before I bought the model shown above, I bought one of the older models on eBay. It had an excellent transmitter, but wouldn’t work for live programming without some modification. I was tempted to break out the soldering iron and tap into the audio line, but with the low price of the newer model, I decided to just get it. The transmitter has two inputs in the back, one for a microphone, and the other for a line-level input, such as from a PA system. These inputs can be used to record a loop on the built-in digital recorder, or for live audio. I tested the unit by recording a program on my MP3 player consisting of music and voice. I set it up in my ground floor home office, stretched out the 3 meter antenna, plugged it in, and went on the air.

You can select any frequency from 530-1700 kHz. When you plug the transmitter, you can hear a small electric motor running the built-in antenna tuner. The assures the best possible antenna match, and the best possible signal. After starting it up, I walked around the house with a portable radio admiring the audio quality. Then, of course, I hopped in the car to see how far I was getting out.

Given the short antenna inside the house, I was absolutely blown away at how well it got out. It easily covered the city block. There were a couple of spots where the signal dropped out slightly, but it was broadcast quality within the block. I kept driving and driving. The signal got weaker, but it was still very listenable several blocks away in most directions. There were spots where it dropped out, but I had almost 100% coverage (with a good car radio) out about a half mile. When I explored further out, I found many “sweet spots” where I had an excellent signal more than a mile away. My best DX was over 2 miles, since there were a few places where I could positively identify my signal at that distance.

I’m astonished at how well this transmitter works. And it is FCC certified as complying with part 15, so there is no question as to its legality. You only have to ensure that you’re using a vacant spot on the dial so as not to interfere with licensed stations. In my case, I use 1610 kHz. In the U.S., that frequency is used only for Traveler Information Service (TIS) stations, and there are none close by.

One might be tempted to purchase an FM transmitter, rather than one for the AM band. There’s a knee-jerk reaction by some that the audio quality is better on FM. That’s not necessarily true, since it depends on the quality of the transmitter. An AM signal can have an excellent frequency response, and the Talking House has excellent audio, probably better than a cheap FM transmitter.

The main problem with buying an FM transmitter is that it’s probably not legal. The requirements for license-free FM transmitters are such that the signal must be extremely weak to be legal. A good receiver 100 feet away probably wouldn’t be able to pick it up. If a transmitter performs better than that, then it’s probably not legal. If you use it for a few minutes per week, you probably won’t get caught. But fines are typically in the range of $10,000 per day, and in my opinion, it’s just not worth the risk, particularly since the Talking House AM transmitter works so well.

There are many uses for this transmitter, and it seems like a very useful item to keep on hand. In addition to drive-in church services and impromptu drive-in movies, it could be very useful to broadcast information in the neighborhood in case of emergency. It comes with a “wall wart” power supply for the 18 volts needed to power the unit. It could be run on batteries, but since the wall wart’s ground lead is an integral part of the unit’s antenna system, it seems best to run it on a small inverter power supply in an emergency, even the smallest of which would be adequate.

One accessory that is necessary if using an external audio source is an audio isolation transformer, to prevent ground loops. When I plug in my MP3 player, it sounds great. But if hook up to an AC adapter, the hum overwhelms the signal. The isolation transformer prevents this. It’s necessary if feeding the audio from any device, such as a computer, that is plugged in to the AC power.

If, for whatever reason, you want to legally broadcast, and have people be able to listen to you up to a mile away, sixty years ago, I would have told you to go to Lafayette or Allied and get a good phono oscillator. And today, it’s even easier. All you need is a Talking House transmitter, and you’ll be on the air the same day your Amazon order arrives.

Jiminy Cricket Endorses Sylvania Tubes: 1940

Jiminy Cricket is no fool, so he endorses Sylvania tubes in this ad shown in the July 1940 issue of Radio Craft. It’s not a magazine ad, but instead a picture of a poster that shops could display. And just to be on the safe side, Jiminy strongly suggests that you should just go ahead and replace all of the tubes while you’re at it, even if they’re still good.

Also shown is a clever business card that probably won’t get thrown away immediately. It’s a disentanglement puzzle, the object of which is to remove the string from the tag without tearing or bending the tag or cutting the string. The photo here isn’t very clear, but it appears to be similar to the puzzle shown in this video.

Those who can’t figure out the puzzle are directed to their nearest Sylvania dealer, where the owner will show how to solve the puzzle, and also solve any radio problems that you might have. And while you’re there, he just might sell you a complete set of tubes to replace the perfectly good ones in the radio at home.

In the past, in lieu of business cards, I’ve used things such as customized rulers, promotional calendars, and wooden nickels. A puzzle made out of cardboard and string probably doesn’t have a lot of staying power, but it will probably get looked at.

Sentinel Postwar Portable

In the final months of the war, American companies knew that they would soon have the ability to produce consumer products, and that there would be a huge pent-up demand for them. Most of them, like Sentinel Radio Corp. of Evanston, Illinois, were planning for that day. Shown here is that company’s vision for what it would produce after the war, a miniature portable that would fit in a vest or shirt pocket or handbag. Smaller than the smallest camera, it was several times smaller than the smallest prewar set.

This model would use a hearing-aid style earpiece, and that wire would double as the antenna. The whole set, including batteries and tubes, would be little larger than the ubiquitous cigarette case.

This teaser appeared 75 years ago today in the July 30, 1945, issue of Broadcasting. The magazine noted that the company was still engaged in war production and wasn’t able to say for sure when the new set would be available. But the new set had passed preliminary tests, and they hoped to start production the moment restrictions were lifted.

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