Jacqueline Hochheiser, Corporate Communications
Over the course of his lifetime, Lee De Forest patented over 300 inventions, but only one proved to be successful and ultimately earned him the title as one of the “fathers of radio.” De Forest invented the Audion in 1906, a device that changed the course of radio history in the 19th century. The three-electrode vacuum tube functioned as a primitive transistor, allowing the amplification of radio signals to enable the broadcast of speech and music, a remarkable upgrade from Morse Code which was the dominant mode of wireless communication at the time.
De Forest was born August 26, 1873 in Council Bluffs, Iowa to Anna Margaret Robbins and Henry Swift De Forest. His father was a congressional minister and moved the family to Talladega, Alabama in 1879 to take on a new position as the president of Talladega College. During his childhood years, De Forest had taken an interest in anything mechanical and kept track of the latest technological advances in the news. By the time he was 13, De Forest could build mechanical gadgets including a miniature blast-furnace and locomotive, as well as a silver-plating device. Some of the smaller inventions he would sell for pocket money.
Although his father wanted De Forest to take up a profession as a minister, De Forest’s passion for mechanics and inventing lead him down a different path. In 1891, he enrolled in the Mount Herman School in Massachusetts completing a three years workload in only two, and graduated a year early. Despite his genius status, De Forest’s disagreeable personality led him to be very unpopular in high school. He was even voted the “homeliest boy” in his class. The criticism, however, didn’t seem to faze De Forest’s oversized ego. A year later, De Forest began his studies in engineering at the Sheffield Scientific School at Yale, which was one of the first schools in the United States to offer a course dedicated exclusively to electrical engineering.
De Forest completed his undergraduate studies in 1896 and decided to stay at Yale for his Ph. D in Radiotelegraphy. His doctoral thesis titled, Reflection of Hertzian Waves from the Ends of Parallel Wires, was a study based on his fascination with radio waves. It was during this time in De Forest’s life that Guglielmo Marconi was making use of Henrich Hertz’s discovery of radio waves with the introduction of the wireless telegraph, the first method employed for long-distance communication using Morse Code.
After completing his Ph. D, De Forest landed a job with the Western Electric Company in Chicago where he started off developing dynamos, electric generators that convert mechanical energy into electricity. He gradually worked his way up in the company to the telephone section and eventually to the experimental laboratory.
After gaining experience in the industry, De Forest transferred to the American Wireless Telegraph Company in Milwaukee, Wisconsin where he produced his first notable invention, the responder. The device was meant to replace the Coherer, which is a radio wave detector containing metal filings inside a glass vacuum tube. Over time, the coherer’s performance would degrade, and it needed to be manually shaken to restore its sensitivity. The responder used liquid electrolytes instead of filings to avoid the need for manual restoration.
The responder was not wildly successful, but De Forest was able to start his first business, creatively named American De Forest Wireless Telegraph Company, in 1902 with the money he earned from selling the device. To draw attention to the business, he traveled frequently to carry out demonstrations of how Morse Code was used to send and receive radio signals wirelessly.
The company was mildly successful after it covered reports on the Russo-Japanese War, which earned him business with branches in the US military. However, the responder was found to infringe on an existing patent owned by Reginald Fessenden and De Forest was forced to cease production at his company and eventually abandoned it in 1907. It wouldn’t be the only business that failed under his supervision, as his prickly personality tended to sour professional relationships, and often ended with De Forest in court defending against fraud or patent infringement.
Inventing the Audion Tube
Despite dealing with setbacks, De Forest had already been in the process of inventing what would become his most successful device, which he patented in 1907, the same year he abandoned his company. The new apparatus was called the Audion.
The Audion Tube
The Audion allowed the design of more sensitive receivers for wireless signals than existing technology. Effectively a primitive transistor, it amplified weak radio signals for which enabled sound, such as speech and music, to be transmitted and received over long distances. This new capability ultimately replaced the need for Morse Code.
De Forest’s Audion consisted of a glass vacuum tube containing three electrodes inside: a cathode (filament), an anode (plate), and a control grid (zigzagging wire). The grid allowed De Forest to modulate the current between the filament and the plate to produce an amplifier, making it the first of its kind capable of both amplifying and modulating electronic signals. It is the amplification of radio waves that allows the signals to be strong enough to carry a larger load (sound).
Schematic of the interior of the Audion Tube
In 1912, De Forest realized that he could cascade Audion tubes to achieve even greater amplification than was possible with just one tube. Later, De Forest revised the design as a regenerative circuit by feeding the output of a single Audion tube back into the device as input power. However, others realized this phenomenon was possible around the same time and the patent for the regenerative circuit was ultimately awarded to E. Howard Armstrong, an American electrical engineer and inventor.
Late Life and Career
After inventing the Audion, he founded the De Forest Radio and Telephone Company using his new invention to broadcast the Metropolitan Opera in New York City, but eventually he and his business partners were accused of mail fraud. Although De Forest was ultimately cleared of the charges, he ended up selling the Audion patent to the American Telephone & Telegraph Company, later known as AT&T, and abandoned his company yet again.
In a change of interest, De Forest decided to pursue the invention of a device that could bring sound to motion pictures that he called the Phonofilm. In 1923, he moved to Hollywood, California to pitch his apparatus to film companies, but none were interested in his idea at the time. It wasn’t until Theodore Willard Case introduced his Movietone system that film companies began incorporating sound into the production of motion pictures.
De Forest lived out the rest of his years in Hollywood, and passed away June 30, 1961. In some ways, his life was a tragic one, he was never wildly successful and nearly every business venture he embarked on ended in failure. He also cycled through many marriages during his life time, all of which resulted in disaster. Of his 300 patents, De Forest’s Audion was the most notable and proved enough to mark him as one of history’s fathers of the radio. This device opened the door for remote entertainment and the transmission of speech and music over long distance, allowing a whole new method of convenient communication.
- Le De Forest | American Inventor (Raymond E. Fielding, Britannica)
- The Audion – History of the Audion Vacuum Tube (History Computer)
- Lee DeForest (PBS)
- Vacuum Triode (Physics and Radio Electronics)
- Audion Tube (NYU.edu/ Physical, Electrical, Digital)
- The Audion (Lee De Forest.org)
- Lee DeForest (National MagLab)