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A RADIO THAT PLAYS
FOR FREE

If someone asked you to name the man who invented radio, you wouldn’t be able to answer him very easily. That’s because a great many men did something important toward making the radio possible. And even though no single person deserves the most credit, certainly among the major contributors was Thomas Alva Edison.

First Electronic Tube

     Edison, in fact, made the world’s first electronic tube, in 1880. Scientists in those days named it the Edison-effect lamp. It consisted of an incandescent lamp into which Edison sealed a small metal plate opposite the filament. The only conducting material the plate touched was a wire leading outside the bulb to a current indicator.

     Edison built this device because he was trying to learn why the insides of incandescent lamps developed a dark coating after a while. He thought maybe current existed in the space within the horseshoe-shaped carbon filament and might be carrying carbon particles to the glass. When he started experimenting he found that every time the lamp was turned on, the indicator registered a reading. The brighter the light, the higher the reading.

     This meant that current was getting from the filament to the plate by traveling through space . . . in other words, with-out wires (which is what the word electronics implies). Although he didn’t realize it, Edison had built the basic radio tube. His patent (no. 307,031) on the Edison-effect lamp eventually became the cornerstone of the electronics industry.