When American inventor Lee De Forest cobbled together a few simple parts back in 1906 – some wires, gas, a light bulb filament – who knew that the resulting creation, dubbed the “Audion,” would one day help power revolutions in communication, computing, and beyond.
This largely overlooked device, predating the transistor by half a century, was nevertheless a key foundation block in our electronic world today. From enabling coast-to-coast phone calls to powering computers that fit in our pockets, the Audion pioneered vacuum tube technology that transformed everyday life.
So how did Lee De Forest’s tinkering bring about one of the 20th century’s most pivotal inventions? Let’s delve into the history and inner workings behind this little tube that could.
Audion 101: Amplifying with Vacuum Tubes
Before jumping into the Audion’s specifics, let’s step back and understand why amplifying electricity was so significant in the first place. For most of the 1800s, electronic signals transmitted by telegraphs and the earliest bulky “wireless” sets decayed too rapidly to travel far. Lunging just 50 to 100 miles at first, these weak signals faded out as electrical resistance converted energy into useless heat. Early submarine cables helped carry telegraphs across oceans – but an electronic means to actively strengthen signals remained elusive.
Experimenters in the early 1900s then discovered thermionic emission, realizing that heated metal cathodes can spew electrons across vacuums toward positive anodes. Britain’s John Ambrose Fleming exploited this effect in 1904’s “Fleming valve” – the first vacuum tube diode. Within a glass bulb housing, this clever gizmo could rectify alternating currents into direct current flows for detecting wireless signals. But it lacked amplification, only weakly collecting electrons via the diode’s voltage.
De Forest envisioned taking rectification further—controlling the current to multiply an input signal’s strength.
| Specification | Fleming Valve | De Forest Audion |
|---|---|---|
| Date Invented | 1904 | 1906 |
| Inventor | John Fleming | Lee De Forest |
| Main Purpose | Rectification | Amplification |
| Components | Cathode, Anode | Cathode, Anode, Grid |
| Max Power Amplification | Minimal (Diode) | 1:50,000+ (Triode) |
The Path to Pioneering Audion “Triodes”
Lee De Forest’s road toward pioneering electronics began at the Yale Sheffield School in the 1890s. While obtaining a Ph.D in electrical engineering in 1899, De Forest grew enthralled by Heinrich Hertz’s recently identified “Hertzian” or radio waves which seemed full of potential to realize “wireless telegraphy.”
“Can these invisible rays, that pass thinly through bricks and stone as if they were glass, be utilized for transmitting intelligence?” a young De Forest wondered with colleagues.
After working briefly under legendary experts like Nikola Tesla and Guglielmo Marconi, De Forest began conducting his own radio experiments using spark-gap generators, coherers, and Marconi’s preferred “aerials” tuned to desired transmission wavelengths. He made improvements like "loose coupler" transformer designs to select specific signals. Yet, he agreed with contemporaries that amplifying signals was “impossible to accomplish” using coherers or crystal rectifiers which crudely demodulated Morse telegraph signals.
De Forest envisioned something far more responsive. In 1902 he proclaimed:
“I discovered that a plate enveloped in a rarefied gas…was amazingly sensitive to electrical resonance. I was sure these were definite indications toward the realization of my long-sought goal – an effective detector of wireless waves!”
After studying rectifying “Branley coherers”, early gas-discharge tubes, and the recently patented Fleming valve’s thermionics, De Forest tried enclosing electrodes in partially gas-evacuated bulbs instead of pure vacuums. Similar to early X-Ray tubes, these became known as “Audions”, partially named after the grid that “audited” currents based on signals received.
“If I insert a third electrode between the filament and plate, it should control the passage of electrons to the plate – thus Achieving Amplification!” De Forest reasoned.
Years of adjustments with gases, vacuums and oxide-coated filaments followed as De Forest patented his Audion detector/amplifier in 1906. Early versions still operated in soft vacuums – but the triode concept was born.
Now for a closer look under the glass at how this little tube worked magic. The Audion’s simple genius lay in manipulating the “space charge” area around a heated, negatively charged filament (cathode). Normally, electrons dispersed quickly unless drawn by an anode‘s positive charge. But inserting a perforated spiral "grid" between filament and plate gave external signals a valve mechanism to govern electron flows.
- Cathode – Filament spews "space charge" cloud of electrons when heated
- Grid – Negative charge repels electrons. Positive charge attracts them, allowing more to reach…
- Anode – Plate collects electrons. More electrons = stronger electrical current flows
So by varying the grid’s charge via incoming signals, radio waves could directly control, divert, and amplify the cathode’s emitted electron stream as the anode collected it – all modulated into audible signals through telephone receivers.
Contemporary spark-gap transmitters generating hundreds of Watts could thereby control over 50 Kilowatts from this tiny amplifier. Vacuum tubes had officially arrived!
Facing Skeptics and Rivals…and Patriots
Despite dramatic long-distance radio demos, slightly "gassy" Audions were dismissed as too temperamental for serious operation by the wireless community in 1906. British Marconi backers instead pushed De Forest out of his own medical wireless company, whose "refusal to consider Audions slowed their development immensely.”
Professionally scorned yet undeterred, De Forest kept tinkering as chief engineer of Federal Telegraph. He publicized Audion achievements like the first ship-to-shore calls from naval radio pioneer Emory S. Land in 1910. After selling Audion rights in 1912 to AT&T engineers who realized its potential for transcontinental telephony, De Forest worked on radio mechanics for the military in World War 1.
Following countless patent challenges between competing radio claimants like Reginald Fessenden, De Forest was recognized as the father of modern radioelectronics. His 300+ patents contributed innovations like Phonofilm sound-on-films, frequency modulation (FM) radio, and the formative "DeForest System" of broadcast programming.
Beyond early radio, Audion tubes powered audio recording, public address systems, even IBM’s early Selective Sequence Electronic Calculator. AT&T installed low-distortion Audions along telephone routes nationwide by 1915 to carry voice – rather than dots and dashes – coast to coast for the first time without signal regeneration. From transmitted entertainment to computers calculating missile trajectories, the Audion channeled electrons where we wanted them to go.
Legacy: Triodes to Transistors
By mid-20th century, engineers sought smaller alternatives to bulky, failure-prone tubes. Solid state physicist William Shockley soon realized the transistor effect in reliable, microscale semiconductors. Integrated circuits packed with microscopic transistors eventually replaced most amplifying vacuum tubes as the active elements in electronics by 1960.
Yet Audion triodes blazed critical foundations now built upon in integrated circuits powering everything from phones to WiFi to computers. Their offspring live on as vacuum fluorescent displays (VFDs). High power versions excel to this day in radio transmitters. Our digitally saturated, networked age owes much to the analog seeds planted by De Forest’s glowing glass bulb called…Audion.
So raise a glass – vacuum tube preferably – to Lee De Forest, whose wireless vision and persistence amplified communications in ways still reverberating today!
