When was Vacuum Tube Invented Answer

Invention of Vacuum Tube Answered 

The wikipedia entry on vacuum tube answers the question of its invention. It is also known as electron tube, valve or just tube. And the answer is the year 1904. And the person responsible for the invention of vacuum tube answered is John Ambrose Fleming. Sir John was a genius. He not only invented the first vacuum tube, he also designed the first radio transmitter which helped send radio signals between two continents, which were later decoded by the receiver, and the famous ‘right hand rule’ used in physics.

Types of Vacuum Tubes

There are two types of vacuum tubes;

-thermionic tubes


Thermionic Tubes

Thermionic tubes have a hot cathode plate placed inside a small vacuum glass chamber with anode at a small distance within it. Electrons are released from the negatively charged plate due to its raised temperature.


Phototubes have a source of radiation such as light thrown on the cathode plate resulting in electrons leaving the negatively charged plate, moving through the vacuum to the positively charged anode.

In both these types of tubes, electrons have no other option but to travel from cathode (negative plate) to anode (positive plate) via vacuum created inside a glass tube. At times small grids are placed between cathode and anode and these individual grids are connected to slightly different sources of voltae (plural of voltage) to help control the flow of electrons from cathode to anode.

A Crucial Invention

The first tube made by Sir Fleming led to the development of radio, television, radar, sound recording and transmitting, long distance telephone networks and analog and early digital computers.

Sir John Amrose Fleming

 Ambrose Fleming was born in Lancaster, England on November 29th, 1849. He had always wanted to be an engineer. It is noted that a young Ambrose had his own workshop, where he built model boats and  engines in his spare time. He performed exceptionally well in maths but disappointingly bad in latin. He built his own camera which started his lifelong interest in photography. His family did not have the financial means to support his dream of becoming an engineer. He, nevertheless, found a way to reach his goal of studying engineering. He worked as a paid employee to earn up to 400 pounds a year for several years and saved almost 400 pounds which he added to his 50 pounds per year of grant money to secure a seat in Cambridge.


The contribution of Sir John Ambrose Fleming to the scientific community and laymen cannot be denied. Although his work is based on the discoveries made prior to his contribution, that still does not rob him of his valuable addition. In hindsight. It can be argued that yes, it was the case. But, hindsight is 20-20. Even if his contribution to the development of radio, tv, radar and long distance communication is ignored on the basis that the knowledge was already available to people. A question does arise then, why nobody made use of it to further technological advancement? I believe, miserable people can never handle others people’s value enriching legacy


Before the advancement of the internet and television, people relied heavily on radio to hear what was happening on a day to day basis around the world. Radios of the time were operating on the principle of amplitude modulated (AM) frequency of radio waves. Voices were imposed on the amplitude of the radio waves to transmit news and entertainment. The rectifying property of diode i.e the property of vacuum tube to allow the current to pass in one direction only is used in a demodulator installed in the radio set which removes the voice from the carrier radio waves and sound it via radio’s speakers.


We all remember those bulky television sets of past years. They had cathode ray tubes, shortened as CRT, to transmit video and audio signals to the home viewer. Cathode plate at the back of television set was electrically charged and the emitting electrons were guided by grids to fall on the positively charged anode screen. It happened so fast that the individual falling of an electron caused a bright spot and no falling electron on the screen caused a black spot. And the continuous hitting and missing made it seem like that the characters on screen are moving and talking.


Radars are both the transmitter and receivers of electromagnetic waves. The source at the center transmits the waves, powered by a giant electric source. As soon they touch something solid in its path, those waves are reflected back by the contours of the shape and are received by the giant bowl part of radar, letting the radar know the precise location and distance from the radar of the said object. As electromagnetic waves move at the speed of the light, it can clearly tell with ease, whether the object hit is stationary or mobile. This knowledge served well in wars.

Long Distance Phone Communication

Lee De Forest’s 1906 invention of triode: a vacuum tube with heated filament, a grid and a plate became very important to amplify weak electrical signals. As the distance between the telephone poles increased, the signals also became weak. With the invention of triode, based on diode (vacuum tube), engineers were able to clearly send the audio signals over the longest lengths of telephonic cables.  

Audio Enthusiasts

Today audio enthusiasts are able to love what they hear, share and create all because of the amplitude enhancing ability of a diode. All the awesome ‘warm sounds’ made by a guitar amplifier, are possible because of this small vacuum chambered oppositely charged electrodes.

Final Thoughts

Sir Ambrose had patented the fleming valve, as he called his invention, in 1905 as a rectifying diode, which was the forerunner to the triode valve and later many related structures, and today it is considered as the father of all the devices that gave birth to the modern electronics. Although, sadly, United States Supreme Court later invalidated the patent claim in 1976 citing an improper disclaimer in the original patent.



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