Category Archives: Radio history

Testing a Battery with a VOM

1970MarEIFifty years ago, Electronics Illustrated showed this pointer for testing batteries with a multitester. Just measuring the voltage won’t do much good, as the battery will probably show its full voltage, even if depleted, with no load.

The solution is to put a resistor in parallel across the battery. If the battery shows full voltage across this 100 ohm resistor, it’s probably good.

These days, multitesters are even cheaper than they were 50 years ago.  In fact, occasionally stores will give them away free.  If you don’t have one around the house, get one, as you won’t know what you did without it.

Some of the meters below give you an idea of how inexpensive they are these days.

If you don’t have that 100 ohm resistor in your junque box, you can also get it on Amazon.

Some links on this page are affiliate links, meaning that this site gets a small commission if you make a purchase after clicking on the link.



1945 One-Tube Four-Stage Receiver & SW Converter

1945MarRadioCraft3Seventy-five years ago this month, the March 1945 issue of Radio Craft magazine carried this one-tube receiver, submitted to the magazine by Sgt. L.R. Blattner, who was stationed at Tinker Field, Oklahoma. According to the serviceman, the set gave the maximum performance for the number of components, and it’s hard to dispute that claim. Despite having only one tube, the set had a stage of RF amplification, AVC, and two stages of AF.

The signal is first applied to the pentode section of the dual tube, passed through the RF transformer, and then detected by the plate and cathode of the triode. Then, it’s applied again to the pentode, now acting as an AF amplifier. From there, the signal goes back to the triode where it’s amplified again.

The magazine also carried the shortwave converter below, sent in to the magazine by Richard E. Held of Sioux City, Iowa, who reported that he received stations from Tokyo to Brazzaville.  It tuned 7-11 MHz, and used two tubes that the writer had lying around.

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School Distance Learning: 1930s

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1937Oct15BCDue to the cornavirus pandemic, schools around the country and around the world are grappling with the issue of how to provide instruction to students by distance learning.  It isn’t a new phenomenon, however, as shown by this article from the October 15, 1937, issue of Broadcasting magazinei

During a Chicago polio epidemic, schools were closed, and the city’s radio stations banded together to broadcast classes for students at home.  The program was so successful that it was to continue even after school was back in session.  Broadcasts would not duplicate material from school, but would supplement it, with a cultural value directed at both adults and children.  The city’s stations would each donate 15 minutes per day of airtime to the programs.

Other schools facing quarantine were looking to Chicago’s successful venture as inspiration for their own.  The Chicago schools had been contacted by educators and broadcasters in the U.S. and Canada for pointers.

The photo above is another example from 1938.  This one isn’t because of an epidemic, but because of a fiscal emergency in Dayton, Ohio, as recounted in an earlier post.

 

 



1945 MacGyver Power Supply

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According to Wikipedia, MacGyver was born in either 1951 or 1952, so he couldn’t have been responsible for this wartime power supply. Instead, it was sent in to the the March 1945 issue of Radio Craft by one Richard F. Reed of Jacksonville, Florida. But MacGyver must have been inspired by Reed, since this power supply ingeniously makes use of available parts, despite wartime shortages.

Reed needed to 90 volt power supply, and used this circuit to get it out of a 1.5 volt battery. The transformer could have been an audio output transformer, but Reed had on hand a model plane induction coil, so he used that. In lieu of an inverter, he used a 1.5 volt buzzer in series with the transformer.

For a rectifier, he used the starter from a fluorescent light. He reported that the supply put out 95 volts at 25 mA.

 



1945 Three Tube Broadcast Set

1945MarRadioCraftThis handsome but utilitarian wartime cigar-box set was put together by G.L. Keirstad of Toronto, and described in the March 1945 issue of Radio Craft magazine. According to the author, the set pulled in all four of the local Toronto stations, as well as WGR and WBEN in Buffalo. At night, it would also get the New York stations with loudspeaker volume quite adequate for a personal radio.

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Stromberg-Carlson 1945

1945Mar12LifeIn March 1945, the war was still on, and that meant that there was no production of civilian radio receivers. But the manufacturers knew that there would be a big sales boom as soon as the war was won, and they were getting their name before the public.

This ad from Stromberg-Carlson appeared in Life Magazine 75 years ago today, March 12, 1945.  And the company was betting on the miracle of FM being the wave of the future.  These young people are listening to some postwar program daydreaming.  The girl dreams of marrying the man of her dreams, and her tenderfoot little brother dreams of being the patrol leader of the best patrol in town.



Is Your Portable Ready to Roll?

1940MarRadioRetailing

On the first warm weekend eighty years ago, this couple were taking their portable radio for a spin around the lake.  It was pulling in the stations thanks to their foresight in bringing it in to the dealer for a free check of the battery and tubes, and a reasonably priced tune-up.

This promotional poster appeared in the March 1940 issue of Radio Retailing.  Presumably, the dealer cut the page out of the magazine and put it in his window or bulletin board.  He then sat back and waited for the portables to start flooding into the store.



1945 “Little Giant” TRF Broadcast Set

1945MarPM31945MarPM1Every year, Popular Mechanics featured plans for a receiver dubbed the “Little Giant,” and these gentlemen are putting together the version described in the magazine’s March 1945 issue.

Despite a war going on, this set was somewhat more elaborate than most.  It featured push-pull audio, with two 6G6-G tubes driving the speaker.  To drop the voltage for the filament string, a 40 watt light bulb was used.  It could be mounted on the chassis, or a lamp could be plugged in to the radio.  The set used a TRF circuit, and the magazine recommended a 75 foot antenna to pull in distant stations.

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1920 Boys’ Life DeForest Radio Ad

1920MarBLOne hundred years ago this month, the March 1920 issue of Boys’ Life carried this ad from the Deforest Radio Telephone and Telegraph Company, 1397 Sedgwick Avenue, Bronx, New York.

Interestingly, I’ve noticed that some ads from this era, like this one, don’t make a distinction between a licensed amateur radio operator, who could transmit, and someone who was just operating a radio receiver as an amateur.  The ad invites boys to write in for a catalog of radio equipment to get the news from everywhere by wireless.  It told them that they could “be an Amateur Radio Operator with your own Receiving Station.”  The ad made clear that the company didn’t sell toys, but instead “practical, scientific Radio Apparatus like that used by Government and Commercial Stations.”  One could start out inexpensively and then build up the station.



Answer to Yesterday’s Quiz

1945MarPSYesterday, we featured this brain teaser from the  March 1945 issue of Popular Science.

At first glance, it looks like it will work.  If you trace the path with button a pushed, bell A should ring.  But what you might not have noticed is that with neither button pushed, both bells are hooked up to the transformer in series.  So they will ring continually, albeit probably at reduced volume.

So wartime shortages or not, Jones will have to scrounge up some additional wire.