A centennial is the 100th anniversary of something important. On the one hand, 100 years seems like a long time; on the other hand, it is a very short time in human history. Essentially everyone who reads this has been around for at least a quarter of a century; probably most readers have experienced a half a century, or close to it. Just about all have relatives who have lived three-quarters of a century and can remember elders, no longer with us, who were born at least a century ago. So 100 years is not that long a time period.
Walter S. Ciciora,
Industry Expert on
Cable & Consumer
The Tube we are celebrating is the vacuum tube, more specifically, the triode vacuum tube. Just 101 years ago, the only thing that could happen to an electrical signal is attenuation; that is, it became weaker. No method existed for taking a weak signal and making it stronger. Because we take amplification for granted today, it is hard to believe that no one knew how to make a weak signal strong.
It started in about 1880 with Thomas Edison and his attempt to figure out why his direct current-powered light bulbs developed a dark coating on the inside of the glass, but just on one side. To try to figure out what was happening, he built an experimental bulb with a small metal plate inside. When he applied a positive potential on the plate, a current flowed, but no current flowed when a negative potential was applied. Edison wasn't sure what was going on, but his automatic reflex was to apply for a patent. It is important to know that an inventor doesn't have to understand how an invention works to get a patent. He merely must be able to explain how to implement the invention. The phenomenon of one-way current flow became known as the "Edison Effect."
An Edison employee in London, John Fleming, became interested in this phenomenon and published papers on his experiments with it. While advising the Marconi Company in 1904, he realized that this device could be used as a radio detector, converting a high frequency alternating current signal into a rectified version which could be filtered to become a useful message. He had invented the vacuum tube diode, which was termed the "Fleming Valve," because it opened to let current flow in one direction, and closed to prevent it from flowing in the opposite direction. In the U.K., vacuum tubes of all kinds were from that point on called "valves." But still, there was no amplification. If the received and detected signal was strong enough to drive a transducer to produce an audible signal, radio reception occurred, but the receiver sensitivity was poor.
In the U.S., another inventor, Lee De Forest, was experimenting with detectors. He studied the technical literature and devised several versions of detectors. De Forest founded a company, the American De Forest Wireless Telegraph Company, to exploit his work, but involved some shady financial types who exploited him, instead. They bankrupted his company. He was allowed to keep the rights to one of his patents, a diode vacuum tube that was very similar, some would say identical, to the Fleming Valve. He called his device the "Audion" and presented a paper to a meeting of the American Institute of Electrical Engineers in New York, one of the predecessors of today's IEEE.
On November 25, 1906, De Forest ordered another batch of Audion tubes, but with a critical difference. He included a third element, a zig-zag wire between the filament and the metal plate. He found that putting potentials on this third element allowed him to control a much larger current flowing between the filament and the plate. He achieved amplification for the first time. The Audion was the first vacuum tube triode. This was the beginning of electronics as we know it.
As already mentioned, an inventor can get a patent on an invention without knowing how it works. All he needs to do is be able to describe how to construct and operate the invention. He doesn't even have to guess at how it works. And, in fact, De Forest was often unable to understand how his inventions worked, offering wildly wrong explanations of the theory of operation. But that does not diminish the importance of the invention itself.
The early story of electronics and radio has many fascinating aspects. The technology, of course, is most interesting, but the history of the people is stranger than fiction. There were dreams of wealth, massive legal fights over patents and patent rights, conflicts over who rightly invented some process or device, and questionable tactics and practices.
Many good books describe the story, some with biases that make one character the hero and the other the heel, while other books reverse the roles. A great book to begin with is "Empire of The Air, The Men Who Made Radio," by Tom Lewis (ISBN 0-06-018215-6). Ken Burns has made a PBS documentary based on this book which is available on DVD.
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