Monthly Archives: May 2015

More 1940 FM Radio

GEHM136

Seventy-five years ago, one apparently dressed up to listen to the radio, especially if you were listening to static-free FM. As related in an earlier post, FM was just starting to gain a modest foothold prior to the war. FM then operated on 42-50 MHz. The Milwaukee station, for example, was on 42.6 MHz. After the war, the FCC moved FM broadcasting to its current home of 88-108 MHz.

To enjoy static-free FM reception, listeners had to get a new radio. At the very least, they would have to get an FM tuner which could plug in to the phono input of their current receiver. The choices were somewhat limited, but many of the major manufacturers came out with at least one FM receiver.

General Electric’s top-of-the-line offering is shown here. It is the HM-136, and is shown in an update on FM in the May 1940 issue of Radio Today.

In addition to the FM band, the 13-tube model covered the standard broadcast band and two shortwave bands, 2.4-7.5 MHz and 7.5-22 MHz. Interestingly, the set didn’t tune the entire prewar band. It tuned only 39-44 MHz, meaning that it wouldn’t be of use in areas with stations higher in the band. Fortunately, however, the existing stations were below 44 MHz, even though the larger band was allocated.

A schematic and service information for the set can be found at Antique Electronics Supply. I haven’t found links to modern photos of surviving examples.

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1940 Postcard Radio

PostcardRadio1Seventy-five years ago, the May 1940 issue of Popular Science carried the plans for this novelty crystal set that was suitable for mailing as a letter. You could slip it into an envelope “and mail to one of your radio-minded friends as an amusing birthday or holiday greeting.”

The radio was sandwiched inside two postcards, with the detector and taps for the tuning coil exposed. Connections for antenna, ground, and headphones were made to paper fasteners which also held the “chassis” together.

To keep it flat, the coil was wound “spider web” style, with four taps for tuning. Blobs of solder were left exposed, and a “crocodile clip” was used to make the connections.

The whole radio could be mailed for six cents.  The schematic is shown below:

PostcardRadio2

All of the parts for this set should be easily obtainable. If you need help finding any (the most difficult to find would be the high-impedance earphone), I have sources on my crystal set parts page.

Click Here For Today’s Ripley’s Believe It Or Not Cartoon



Visit Us at the Duluth-Superior Hamfest

We will be at the Arrowhead Amateur Radio Club Hamfest in Superior, Wisconsin, this Saturday, May 2. If you’re in the area, stop by and say hello! I’ll have copies of my books available: My study guides for the Technician and General class amateur licenses, the MROP and GROL commercial licenses, and my novel Caretaker, all at special Hamfest prices.

Interestingly, the Hamfest is located less than a mile from the transmitter site of W9XJL, Duluth-Superior’s 1930’s shortwave broadcast station.

WCCO Radio in 1925

WCCOstudio1925For those interested in the early history of WCCO radio in Minneapolis, the May 1925 issue of Radio Age carried a feature on the station as it was 90 years ago. The station had just put into service its new 5000 watt transmitter, what the magazine called “one of the super broadcasting units.” It also noted that the Minneapolis studios at the Nicollet Hotel were “said to be the equal both in equipment and elegance of anything in the country.”

In addition to the Minneapolis studio, the station had just begun construction of a studio in St. Paul, which would probably be “the most unique location of any studios in the world, for they will be in Saint Paul’s handsome new Union Depot used by nine railroads.”

The transmitter was at the station’s current transmitter location, 18 miles northwest of Minneapolis in Anoka. Special telephone lines connected the studios and transmitter.

The station had come on the air in October 1924, using the equipment of the former WLAG.

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