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Audion Vacuum Tube

Let‘s Explore the Remarkable History of the Audion Vacuum Tube and Its Pivotal Impact on Technology

The Audion vacuum tube was one of the most pivotal inventions in the history of electronics and enabled the technology revolution of the 20th century. Developed in 1906 by American engineer Dr. Lee de Forest, this remarkably simple device allowed electrical signals to be amplified, switched, and controlled like never before possible.

The triode Audion paved the way for transcontinental telephones, radio broadcasting, television, radar, digital computers, and countless later advancements. Here we will delve into the fascinating history of the Audion tube and its tremendous contributions that still echo through modern technology today. Let‘s get started!

Harnessing the Power of Vacuum Tubes

Our story begins in the late 1800s, when scientists were intensely investigating the curious properties of vacuum tubes. They discovered that large currents could flow between a negatively charged "cathode" filament and a positively charged "anode" plate inside a glass tube devoid of air.

This phenomenon depended on thermionic emission – essentially, heating the cathode caused it to eject electrons that would flow to the anode. Current would also flow the other way if the polarity was reversed.

Thomas Edison first observed this effect in 1883. He called it the "Edison effect" but didn‘t pursue it further. In 1904, British physicist John Ambrose Fleming exploited vacuum tube rectification to create the first true vacuum tube device – the Fleming valve diode. This was used to detect radio signals, but amplification remained elusive.

The stage was now set for Lee de Forest to revolutionize the fledgling field of electronics with his Audion…but first, who was this pioneering inventor?

Lee de Forest: The Father of Radio

Lee de Forest photo portrait
Lee de Forest, pioneer of radio and vacuum tube technology. Image credit:

Lee de Forest (1873-1961) was a world-changing American inventor with over 300 patents. He grew up in Alabama and became fascinated by electricity and telegraphy as a child. In 1896, de Forest received a PhD in physics from Yale and began experimenting with wireless telegraphy.

De Forest made several key breakthroughs in the early 1900s that laid the foundations for radio. In 1906, he developed an improved radio transmitter called the "oscillation valve." The next year came his magnum opus – the Audion vacuum tube.

This brilliant yet controversial inventor endured many ups and downs during his lifetime. He faced patent battles, failed businesses, financial troubles, and even an indictment for mail fraud (later exonerated). However, de Forest‘s technological legacy lives on. As the New York Times wrote, "Few inventors contributed more to modern America." Next let‘s explore his amazing Audion tube and the waves it caused.

The Audion Vacuum Tube: A World-Changing Invention

Diagram of De Forest's Audion tube
Diagram of de Forest‘s pioneering Audion tube design. Image credit:

Building on earlier "diode" vacuum tubes, de Forest added a third electrode to make what he called the "Audion." This was a grid of wire placed between the cathode filament and anode plate. By applying a small voltage to the grid, it could control a much larger current flowing between the other two electrodes.

This amplification effect occurred because the grid was located in the prime electron flow path. A weak signal applied to the grid could thus modulate stronger internal currents.

De Forest filed successful patents for his Audion tube in 1906 and 1908. Its ability to amplify signals was quickly realized around 1912, powering breakthroughs like:

  • Vacuum tube amplifiers – Developed by AT&T, Westinghouse, GE, and other companies for industrial applications.
  • Vacuum tube radio – Audion tubes enabled sensitive radio receivers and powerful transmitters, allowing public broadcasting to begin around 1916.
  • Transcontinental phone lines – Bell System engineers used Audion repeaters to amplify signals across thousands of miles of phone cable.
  • Electronics – Vacuum tubes became essential components for countless electronic systems and early computers over subsequent decades.

Let‘s explore some of these revolutionary applications of the Audion tube and its impact on society in more detail.

Radio Broadcasting Takes Off

During the 1910s and 1920s, vacuum tube technology transformed radio from a niche into a mainstream phenomenon. Early crystal detector sets had limited range – often just 25 miles or less. But Audion tube receivers could pick up stations hundreds or even thousands of miles distant.

By 1923, over 500 commercial AM radio stations crowded the airwaves in the United States. The Radio Act of 1927 and formation of the Federal Radio Commission brought order to this chaos. But the Golden Age of Radio had definitively arrived, with audition tubes powering both receivers and transmitters.

Vintage radio promotional advertisement
Vacuum tube radio advertisement, 1920s. Image credit:

Radio sets became enormously popular. By 1930, over 60% of American families – some 18 million households – owned a radio. Americans became glued to radio favorites like Amos ‘n‘ Andy, The Lone Ranger, and Franklin D. Roosevelt‘s "fireside chats."

The radio craze drove exponential growth in vacuum tube production. In 1922, only 1 million tubes were made in the U.S. But just 5 years later, in 1927, that figure had skyrocketed to 200 million!

Connecting the World by Telephone

Another vital early application for the Audion was in telephone networks. AT&T engineer Harold Arnold developed reliable vacuum tube voice amplifiers by 1912. The company soon began installing them to boost signals on long distance lines.

With Audion tube repeaters spacing every 20-30 miles down the cable, telephone calls could now span unprecedented distances. This made transcontinental phone service a reality, connecting New York to San Francisco in 1915.

By 1930, telephone calls could traverse the Atlantic. Vacuum tube amplifiers became essential components enabling global telephony. At its peak in the 1950s, AT&T operated some 24 million tube amplifiers in the U.S. phone network alone!

Vintage 1930s telephone switchboard operators
Vintage 1930s telephone switchboard operators. Image credit:

Many other communication applications also emerged. For example, Bell Labs engineer Edwin Armstrong used Audion tubes to invent wideband FM radio in 1933. This higher fidelity broadcasting, along with vacuum tube Hi-Fi stereo systems, brought music to life as never before.

Birth of the Digital Computer Age

Vacuum tubes were integral building blocks of the first general purpose digital computers in the 1940s. Early electronic computing pioneers recognized tubes offered ideal properties for processing binary data.

For one, tubes could serve as fast electronic switches. Their nonlinear response allowed them to cleanly flip between on and off states representing 1s and 0s. This was ideal for implementing logic gates and digital operations.

Tubes also functioned as memory. Dynamic random access memory (DRAM) using the grid storage principle was developed. Static Williams tube designs stored data as electrostatic charges on CRT screens.

Finally, tubes amplified signals between logic circuits. This allowed fan-out to multiple gates – a basic requirement for digital logic.

The seminal ENIAC computer finished in 1946 used over 17,000 vacuum tubes! It could perform 5,000 additions per second, a massive achievement. Other major tube computers like EDSAC, UNIVAC, and Whirlwind followed. Their military and scientific calculations helped launch the computer revolution.

Atanasoff-Berry Computer
The Atanasoff-Berry Computer, 1939-1942, contained over 300 tubes! Image credit:

However, tubes used prodigious amounts of power and produced severe heat. The ENIAC weighed 30 tons and consumed 150 kW of electricity! Reliability was also a challenge with so many failure-prone components. By the 1950s, researchers began seeking out smaller, cooler, more robust alternatives. The resulting invention of the transistor marked the end of vacuum tubes for computing.

Cathode Ray Tubes Usher in Television

Television represents another defining application for vacuum tubes. Early TV camera tubes like the Iconoscope and Vidicon converted optical images into electronic signals for transmission.

Receiving sets used cathode ray tubes (CRTs) to recreate the video images. Electron beams scanned across phosphor-coated screens activated the glow of pixels. This technological marvel turned television from science fiction into reality during the 1930s.

After being halted by WWII, consumer television exploded in popularity during the 1950s. By 1955, almost two-thirds of American homes boasted a TV set. Broadcasting expanded from just a few networks and stations to the cornucopia of cable channels we enjoy today.

The Apollo 11 moon landing on July 20, 1969, represents perhaps the peak of vacuum tube television. An estimated 600 million people worldwide watched Neil Armstrong take his "one small step" broadcast from the lunar surface. This truly astonishing technical feat was enabled by vacuum tubes.

Vintage CRT television set advertisement
A 1950s advertisement for CRT vacuum tube televisions. Image credit:

The Vacuum Tube Legacy

By 1960, smaller and cooler semiconductor technology like transistors and integrated circuits had largely displaced bulky vacuum tubes. Tubes were obsolete for most cutting-edge applications. However, the concepts pioneered during the tube era became foundational for modern electronics.

Vacuum tubes directly inspired solid-state devices like the point-contact transistor, junction transistor, and MOSFETs. Integrated circuits package thousands of microscopic transistors on chips yet operate on principles remarkably similar to vintage tube circuits.

The information age we live in today with ubiquitous computing, communication, and entertainment owes a great debt to vacuum tube technology invented at the turn of the 20th century. Those early pioneers with their glowing Audion bulbs could scarcely have imagined the world their creations enabled.

Of course, nostalgia keeps vacuum tubes alive in niche retro applications. Audiophile headphone amps and guitar stacks use tubes to produce pleasing analog warmth and distortion characteristics. Hobbyists restore vintage radios to working order using "new old stock" tubes. The magic of these early electronic amplifiers lives on.

So the next time you pick up your smartphone, download a podcast, or video chat with a loved one halfway around the world, pause to reflect on the history of technology that made it possible. The pioneering spirit of Dr. Lee de Forest and the remarkable Audion vacuum tube created our electronic age.