Lee De Forest 1873 - 1961

Father of the electronic amplifier. Also known as the father of American radio, though the latter title, it would seem, is not really justified.

Lee DeForest is best known by the technologists for improving John Fleming's thermionic diode valve by adding a third electrode, known as the grid. This simple addition changed the face of electronics. The triode valve became the first effective amplifier and made possible the modern telephone system as well as much of the modern electronic world.

In conceptual terms, the triode valve is the forerunner of the electronic transistor. Triodes and transistors can both be configured to act either as amplifiers, so that the output signal corresponds to fluctuations in the input signal; or as switches, in which a small change in the input flips the output between two extremes.

When a transistor is configured as a switch, it becomes the most fundamental element of a digital computer. Thus, DeForest's 1906 invention was one of the most significant technological steps on the road to the modern digital computer.

But there's a lot of history to get through before we arrive at the digital computer.

A hundred years ago, there was no science of electronics. We knew about motors and generators. We knew about lighting circuits. We knew about magnetism. But we didn't really understand what caused these effects, or how they were bound together by electrons and fundamental forces and quanta and other sciency stuff.

One of the most peculiar aspects of physics of the final years of the 19th century was that the world's top physicists, led by Lord Kelvin (1824 - 1907) thought there was nothing more to learn. There appeared to be just a few loose ends--unexplained phenomena--to tie up. Kelvin and his peers knew the world was made up of tiny solid, indivisible billiard balls called atoms and the atoms were arranged according to the periodic table of the elements. and they behaved according to the rules discovered by Newton a couple of hundred years previously.

The most intransigent problem of physics at that time was the so-called ultra-violet catastrophe. Max Planck sorted that one out in 1900 and in doing so coined the phrase quantum physics.

The second most intransigent problem of the time was called the photoelectric effect. That one was sorted by an obscure Austrian physicist called Albert Einstein in 1905.

Some of the other stuff going on at the time included Wilhelm Röntgen's discovery of x-rays (1895); JJ Thompson's discovery that cathode rays are comprised of charged particles (1896); Marie Curie's investigations into radioactivity (1898) Marconi's first radio broadcast (1895) and his first transatlantic transmission (1902) and Ernst Alexanderson's high frequency alternator (1901). Wilbur and Orville Wright's first flight at Kitty Hawk (1903)

There was also a lot of interest in spiritualism and ectoplasm at the time. Today we know X-rays and cathode rays are genuine physical phenomena, and we think that ghosts and ectoplasm are imaginary, but at the time they were all mysteries that needed to be explained and de-mystified.

Because of all this activity and new thinking, the decade from about 1895 to 1905 was one of the most exciting and fast-moving that the world of physics has ever seen. In a few short years, the old order was smashed up and everyone had to re-think their world-view. The physicists had to destroy the idea that atoms were indivisible, and replace atomic theory with a new one, based on quanta; on sub-atomic particles and all sorts of other very new-fangled ideas.

Getting back to the thermionic valve.

Cathode rays, X-rays and early illuminated bulbs all use a similar apparatus: a glass bulb with some wires stuck inside and containing nothing but a vacuum. Most of the people who played with these things were able to make their own glass bulbs and stick wires into them and pump air out of them. That meant there was a lot of cross-over between the people who were playing with cathode rays and X-rays and the people who were trying to make a reliable, long-lasting light bulb. And that means a lot of the inventions relied on similar ideas and technologies

In the year or two before 1880, both Sir Joseph Wilson Swan and Thomas Alva Edison had made practical electric light bulbs using incandescent filaments that lasted 10 to 20 hours. Over the following years they gradually improved their inventions. By the turn of the century a few luxurious houses were lit by these modern wonders, using filaments made from carbonised bamboo or other materials. it wasn't until 1906 that the General Electric Co used tungsten as a filament.

Bringing together a number of these ideas, Fleming used a carbon filament to heat a metal plate, all held in a glass vacuum tube. He put voltages on one side and then the other and discovered that, under certain conditions, he could make current flow one way across the gap, but not the other. That was in 1904.

This was quite a revelation, because all previous electrical devices were symmetrical. They behaved the same way no matter which way around they were connected. It was also useful because this new rectifier could decode a signal which had previously been amplitude modulated. While the device is useful in radio telegraphy; it could only be used with Morse code and other on-off signals. it wasn't capable of sending or receiving voice or music.

To summarise, Fleming's diode valve comprised a heated plate and another electrode, all enclosed in a glass vacuum tube. Using modern theory, the heated plate would normally give off electrons (cathode rays) by thermionic emission. if the cathode is made negative, ( a surplus of electrons) then a small current will flow quite happily across the gap. If, however, the cathode is made positive (a dearth of electrons) then the current stops flowing.

Finally, getting back to De Forest; his primary contribution was to put a fine mesh grid in between the heated plate (cathode) and the anode.

The set-up is slightly different from Fleming's diode valve. While the working principles are similar, the effect is far-reaching. In De Forest's triode, The heated cathode is kept at a negative charge, while the anode is kept positive. The heat under the cathode keeps a nice, steady flow of electrons boiling off the heated plate. With no voltage on the grid, all these electrons stream across the gap to the anode, where they are attracted by the positive charge.

If the grid has a small positive charge, it will suck electrons off the plate, accelerating them across to the grid. Once they pass through the mesh-like grid, the strong positive voltage on the anode accelerates them even more and they stream towards that. The valve becomes a closed circuit.

If, on the other hand, the grid has a negative charge, then the thermionic electrons won't have enough energy to overcome the electrostatic field generated by the grid. All the electrons will be repelled back into the plate, so no current flows across the valve. The valve is thus an open circuit.

The critical thing is between those two extremes. At some point between fully on (grid+) and fully off (grid-), a small increase in positive charge on the grid makes a big difference to the number of electrons flowing across the gap. The current across the valve is directly proportional to the voltage on the grid.

And that means small changes in charge on the grid can lead to big changes in current across the valve. De Forest's Audion--for so he named the invention--was a prototype amplifier. It's quite important to balance the voltages on the three electrodes and also the spacing between them, but there is a fairly wide margin of error in the setup.

The rest, as they say is history. DeForest set up a company--the DeForest Radio Telephone Company-- in 1907, shortly after he patented the Audion. He broadcast many key events to the US public and sold receivers based on the Audion valve. He made a fortune, but spent most of it on lawyers' fees defending his many patents.

One small footnote: GE was leading the race to effective broadcasting of speech and music, based on Alexanderson's alternator, which allowed broadcast on wavelengths around 3000 metres, combined with the ideas of his boss, Charles Steinmetz. In 1916 DeForest scored a notable first when he broadcast the results of the presidential election between Woodrow Wilson and Charles Evans Hughes.

It should have been a triumph, but DeForest wanted to stop broadcasting early, and failed to take the California result into account. The first presidential broadcast therefore called Hughes the winner when, as we all know, WIlson won the White House.


A life

DeForest was born in Council Bluff, Iowa on 26 August, 1873. Shortly after, his family moved to Alabama where his father--a congregational minister--had taken the controversial post of head of a school for black people. After his initial schooling, De Forest attended Yale, where he gained a degree in 1896.

HIs Ph.D thesis on high-frequency oscillation effects in parallel wires signalled his passion for radio, and was one of the earliest papers to set out the possibilities of long-distance radio broadcasting. Effectively he set out the science of a broadcast aerial and the receiving antennae.

After that, DeForest got a job with the Western Electric Company in Chicago, working on dynamos. Two years later, in 1901, he quit and helped edit the magazine Western Electrician while doing some part-time teaching and inventing. In 1902 he founded the DeForest Wireless Telegraphy Company, and his receiving apparatus won a gold medal for the best wireless system at the 1904 World's Fair in St. Louis.

He filed a patent on a two-electrode Audion tube in 1906 and the following year patented the three-electrode (triode) thermionic valve. Almost immediately, he founded a new company, the De Forest Radio Telephone Company. In 1912 he sold the patent (US879532) and rights to the triode Audion to AT&T for use in telephone systems.

In 1912 another radio pioneer, Edwin Armstrong adapted the Audion tube. First, Armstrong worked out what was really going on in the Audion--something De Forest never quite managed. Second, he cycled the output back to the input many times over (patent granted 1914). He christened the process regeneration, and it was a way to use the Audion tube as a compact, energy-efficient transmitter. Armstrong added the superhet and made radio into a real commercial system.

De Forest patented a very similar regenerative process in 1916 and sold that patent to AT&T. The consequent legal battle between Armstrong and De Forest became the longest in American legal history, lasting from 1922 to 1934. DeForest took the case all the way up to the Supreme Court, losing at every step. but in 1934, in an historic ruling, that even now most radio engineers believe to be based on a failure properly to understand the technicalities, a Supreme Court judge ruled that all these inventions belonged to De Forest.

Armstrong was not the only man to suffer from De Forest's talent for 'borrowing' others' ideas. Although De Forest deserved great acclaim for his Audion and a few other inventions, he chose his business partners badly and had a habit of claiming for himself the ideas of others. This eroded whatever respect the engineering community may have had for him, and he lost many of the honorary posts that his technical success had brought.

In the later years, DeForest worked on his own inventions and for other companies over the following years, gaining a number of accolades and professional recognition for his radio work. He gave his autobiography the somewhat self-aggrandised title Father of Radio. It has to be said, however, that if there is one single father of American radio, that title probably belongs to Edwin Armstrong.

In 1959 (awarded in 1960) he won an Honorary Oscar for services to the Motion picture industry. the citation reads, "for pioneering inventions which brought sound to the motion picture" and he also won a star on Hollywood's walk of fame (located at 1752 Vine Street.

DeForest died in 1961 in Hollywood.

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