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One-Tube Radio Can Be Mailed
June 1947 Popular Science

June 1947 Popular Science

June 1947 Popular Science Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Popular Science, published 1872-2021. All copyrights hereby acknowledged.

Do you remember when the musical greeting cards with the integrated microchip and speaker for playing a jingle first appeared in stores like Hallmark? They, along with cards having flashing LEDs were showing up in display racks sometime around 1990, and cost about $10 (~ $24 in today's money). The sound quality was low, but its novelty overrode the tinny, digital timbre. This 1947 article from Popular Science had what might have been the world's first mailable electronic greeting card. It did not have a programmed integrated circuit onboard, but did incorporate a complete AM radio circuit, including a "peanut" tube for amplification. Unlike modern musical cards that have an onboard coin cell for power, this one required the recipient to connect his own "A" (1.5 V) battery and "B" (22.5 V) battery to get it working. He would also need a set of headphones as there was no built-in speaker (see photo). Still, it was a novel and intriguing concept at the time, demonstrating the advance in component miniaturization in the day. I don't recall seeing advertisements in my many hundreds of vintage electronics and technology magazines pitching electronics greeting cards, so I'm guessing the idea never made it to the commercial market phase.

One-Tube Radio Can Be Mailed

Fitting parts into slots in the cardboard chassis makes the set flat and also guards the components.

Small crocodile clips soldered to the various detachable leads permit quick and easy connection.

Resistors are 1/4 watt, and the tubular condensers 200 volts; phone impedance should be 2,000 ohms.

Tube leads may be identified by the position of the red spot. The coil is wound on a cardboard circle.

By Albert Rowley

Subminiature tubes measuring less than 1/4" in diameter will make it possible to redesign radio circuits to almost any shape and size. This novelty receiver is as flat as the tube itself and can therefore be inserted in a 6" by 9" envelope and sent through the mails as a letter. The two pieces of 1/8" cardboard that form the chassis are held together by the same nuts and bolts that hold the phone, battery, antenna and ground terminals in place. Slots are cut in the cardboard to clear the components.

The tiny 2E32 tube is a shielded pentode and operates with a plate voltage of 22 1/2 and a filament voltage of 1 1/4. For the latter, a small flashlight cell will give several hours of useful life. One of the miniature 22 1/2- or 30-volt batteries will supply both the plate and the screen.

To keep the receiver flat, the coil is wound on a cardboard disk 4" in diameter. Cut 13 slots at intervals of approximately 1" as shown in the sketch below; then interlace the form with 92 turns of No. 30 enameled wire. At every twelfth turn, make a tap by scraping the enamel and letting a drop of solder adhere to the spot.

Although the circuit doesn't employ regeneration, it has sufficient power to pull in local stations. By selecting the right antenna and ground taps and adjusting the trimmer in the antenna lead, it should be possible to cover the entire broadcast band. The trimmer specified in the drawing is intended for use with a short indoor antenna; if used with a long antenna, a trimmer of lower capacity - say 125 to 350 mmf. - should be substituted.

 

 

Posted January 5, 2024

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