原创 Milestones in eletronics: From light bulbs to computers

Here's a quote from Popular Mechanics, 1949:

Where a calculator on the ENIAC is equipped with 18,000 vacuum tubes and weighs 30 tons, computers in the future may have only 1,000 vacuum tubes and perhaps weigh 1-1/2 tons.

November marks the 40th anniversary of the microprocessor, the circuit element that truly revolutionized the world and gave birth to the field of embedded systems. This is the second installment about this historic development. You can find the first here: The microprocessor at 40—The beginning of electronics (Part 1)

Thomas Edison raced other inventors to develop the first practical electric light bulb, a rather bold undertaking considering there were neither power plants nor electrical wiring to support lighting. In the early 1880s his bulbs glowed, but the glass quickly blackened. Trying to understand the effect, he inserted a third element and found that current flowed in the space between the filament and the electrode. It stopped when he reversed the polarity. Although he was clueless about what was going on—it wasn't until 1897 that J. J. Thomson discovered the electron—Edison filed for a patent and set the idea aside. Patent 307,031 was for the first electronic device in the United States. Edison had invented the diode.

Which lay dormant for decades. True, Ambrose Fleming did revive the idea and found applications for it, but no market appeared.

In the first decade of the new century, Lee De Forest inserted a grid between the anode and cathode, creating what he called an Audion. With this new control element a circuit could amplify, oscillate, and switch—the basic operations of electronics. Now engineers could create radios of fantastic sensitivity, send voices over tens of thousands of miles of cable, and switch ones and zeroes in microseconds.

The vacuum tube was the first active element, and its invention was the beginning of electronics. Active elements are the core technology of every electronic product. The tube, the transistor, and, I believe, now the microprocessor are the active elements that transformed the world over the last century.

Even though the tube was a stunning achievement, it was useless in isolation. De Forest did create amplifiers and other circuits using tubes. But the brilliant Edwin Armstrong was probably the most seminal early inventor of electronic circuits. Although many of his patents were challenged and credit was often given to others, Armstrong was the most prolific of the early radio designers. His inventions included both the regenerative and super-regenerative receivers, the superhetrodyne (a truly innovative approach used to this day), and FM.

As radio was yet another communications technology, not unlike SMS today, demand soared as it always does for these killer apps. Western Electric made the VT1, one of the first commercial tubes. In 2011 dollars, they were a hundred bucks a pop. But war is good for technology. In the four years of World War I, Western Electric alone produced a half million tubes for the U.S. Army. By 1918 over a million a year were being made in the U.S., more than 50 times the pre-conflict numbers; prices quickly fell. Just as cheaper semiconductors always open new markets, falling tube prices meant radios became practical consumer devices.

Radio
Start an Internet publication and no one will read it until there's "content." This is hardly a new concept; radio had little appeal to consumers unless there were radio shows. The first regularly-scheduled broadcasts started in 1919. There were few listeners, but with the growth of broadcasters, demand soared. RCA sold the earliest consumer superhetrodyne radio in 1924; 148,000 flew off the shelves in the very first year. By the crash in 1929, radios were common fixtures in American households and were often the center of evening life for the family, rather like TV is today.

Nearly until the start of World War II, radios were about the most complex pieces of electronics available. An example is RCA's superb RBC-1 single-conversion receiver, which had all of 19 tubes. But tubes wore out, they could break when subjected to a little physical stress, and they ran hot. It was felt that a system with more than a few dozen would be impractically unreliable.

One hundred tubes and counting
In the 1930s, it became apparent that global conflict was inevitable. Governments drove research into war needs, resulting in what I believe is one of the most important contributions to electronic digital computers, and a natural extension of radio technology: RADAR (radio detection and ranging). The U.S. Army fielded its first RADAR apparatus in 1940. The SCR-268 had 110 tubes... and it worked. At the time tubes had a lifetime of a year or so, so one would fail every few days in each RADAR set. ("Set" is perhaps the wrong word for a system that weighed 40,000kg and that required six operators.) Over 3,000 SCR-268s were produced.

Ironically, Sir Henry Tizard arrived in the U.S. from Britain with the first useful cavity magnetron the same year the SCR-268 went into production. That tube revolutionized RADAR. By war's end, the 10-cm wavelength SCR-584 was in production (1,700 were manufactured) using 400 vacuum tubes. The engineers at MIT's Rad Lab had shown that large electronic circuits were not only practical, they could be manufactured in quantity and survive combat conditions.

[To be continued at Milestones in eletronics: From light bulbs to computers (Part 2)]