GoKawiilWilliam Shockley, John Bardeen, and Walter Brattain, winners of the 1956 Nobel Prize for their work on the “transistor effect.” Via Wikipedia .
As we’ve noted more than a few times before, for most of the 20th century AT&T’s Bell Labs was the premier industrial research lab in the US. As part of its ongoing efforts to provide universal telephone service, Bell Labs generated numerous world-changing inventions, and accumulated more Nobel Prizes than any other industrial research lab. But the most important of its technical contributions proved to be useful far beyond the confines of the Bell System. Statistical process control, for instance, was invented by AT&T engineer Walter Shewhart to improve the manufacturing of AT&T’s electrical equipment at supplier company Western Electric. Since then, the methods have been successfully applied to all manner of manufacturing, from jet engines to semiconductors to container ships.
Interestingly, some of AT&T’s most important technological contributions — namely, the vacuum tube, the negative feedback amplifier, the transistor, and the laser — were (in whole or in part) the product of efforts to make new, better amplifiers for boosting electromagnetic signals. Amplifiers played a crucial role in the Bell System, making it possible to (among other things) connect telephones over long distances, but the value of these four amplifiers extended far beyond telephony. The vacuum tube became a crucial building block for electronics in the first half of the 20th century, used in everything from radio to television to the earliest computers. The negative feedback amplifier helped spawn the discipline of control theory, which is used today in the design of virtually every automated machine. The transistor is the foundation of modern digital computing and everything built on top of it. And the laser is used in everything from fiber-optic communications to industrial cutting machines to barcode scanners to printers.
It’s worth looking at why AT&T was so motivated to build better and better amplifiers, and why those efforts produced so many transformative inventions.
The vacuum tube
In 1876 Alexander Graham Bell placed the world’s first telephone call, summoning his assistant Thomas Watson from another room. By 1881, Bell’s company, the Bell Telephone Company (it wouldn’t become American Telephone and Telegraph, or AT&T, until 1899) had 100,000 customers. By the turn of the century AT&T was operating 1,300 telephone exchanges in the US, connecting over 800,000 customers with 2 million miles of wire.
The goal of the Bell System was “universal service” – to connect every telephone user with every other telephone user in the system. But by the early 20th century this quest was bumping up against technological limitations.
Telephones converted the sound of someone speaking to electrical signals, which were transmitted along wires until reaching a telephone on the other end, where they were converted back into sound. More specifically, in early telephones the sound from someone speaking would compress and decompress a chamber full of carbon granules, which would alter their electrical resistance, changing how much current flowed through them. At the other end, the electrical current would flow through an electromagnet, which pulled on a thin iron diaphragm; fluctuations in the electrical current would change the motion of the diaphragm, reproducing the speech.
But the farther electrical signals travelled, the more they would be attenuated. Resistance from the wire carrying them would convert some of the electrical energy into heat, and electrical current could “leak” between adjacent telephone wires. As the electrical signals got weaker and weaker, the sound would be less and less intelligible when reproduced, until it couldn’t be heard at all. If AT&T wanted to provide universal service, it would need a way to maintain the strength of the electrical signal as it traveled over long distances.
AT&T was able to partly resolve this problem using the loading coil, an invention of electrical engineer Michael Pupin. (Lines which had loading coils added to them were sometimes described as being “Pupinized.”) The loading coil added inductance (a tendency to resist changes in current) to telephone lines, which reduced signal attenuation. As a result, the loading coil roughly doubled the effective distance limit of telephone calls, from around 1000-1200 miles to closer to 2000 miles. But the loading coil merely reduced signal attenuation; the signal was still decaying as it traveled along the lines, just more slowly. Without some way of actually amplifying the telephone signals, the maximum distance for a telephone line was enough to connect New York to Denver, but not enough to reach the West Coast from New York and connect the entire country.
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