The story behind the invention of vacuum tube  

Anything in Science has its own history and some hidden truths behind its invention. It must be fascinatingly curious for any science savvy person to know the invention story of technical tools, and other innovations of Science. This is one such write up which will help you know about the researches and the advancements in the invention of the vacuum tubes.

Vacuum tube?

Vacuum tubes are sealed glass tubes made of vacuum that facilitates the passage of electric current. They are also called as electron tubes and they may be sealed either with glass or with a metal ceramic mixture. The application of this invention does not stop with a single one. They serve multiple purposes like amplifying a weak current, converting an alternative current (AC) to direct current (DC), for the generation of oscillating radio frequency.

The inventors!

If there is something awesome, it is true that great minds are involved in its invention. Professor Guthrie, Thomas Alva Edison, Ambrose Fleming, Lee de forest, William.D.Coolidge, Walter schottky and Irving Langmuir were those brilliant minds that were involved in the advancements of the electron tube.

The first leap! 

Professor Guthrie
Professor Guthrie - Copyright:- Wikimedia Foundation

It was Professor Guthrie who first worked with the unnamed vacuum tubes in the mid eighteenth century. He observed an effect, which showed, when a red hot iron sphere was negatively charged, it could discharge. But on the contrary, if the same hot sphere was positively charged, it did not get discharged! This remained as an unsolved puzzle until Edison made his move.

The solution for puzzle by Edison! 

Thomas Edison - Copyright:- Wikimedia Foundation

In 1883, Edison made an excellent move. When Edison was working with the incandescent lights and other bulbs, he faced a major problem. It was that the bulbs got blackened so quickly. Edison found that this was because the negatively charged particle hit the surface of the light bulb. He then made an alternative by placing positively charged particles. As we all know the fact that opposite charges attract each other. The negative charges were attracted by the newly introduced positive charges and thus it was prevented from hitting the surface of the bulb. He also found that when the second element was positive, then a current flow was occurring in the circuit. But, reversing the potentials averted this process. This was named as Edison effect and its purpose was unidentified. He discussed this effect with an electrical engineering professor from University College, London. He was Ambrose Fleming.

Further advancements in the discoveries 

John Ambrose Fleming:- Copyrght:- Wikimedia Commons

Only with the advancements by Professor Fleming, it was known that the atom had finest particles called electrons. And the reason for why it attracted the positively charged particles was identified by Sir Joseph Thomson. In 1889, when Fleming was working with the same Edison effect, he observed that when an alternative current was passed between 80 to 100 Hertz of frequency, only half of the cycle was completed. This was the observation that led to the above mentioned understanding that electrons were released from the heated filament.

The oscillation valve by Fleming

Marconi was working on wireless signals and was trying to increase the distance up to which they can be made to use. Fleming was working with Marconi. He observed that the sensitivity of the receiving tool was due to the detector’s lack of sensitivity. Coheres and magnetic detectors were employed which were of no better capacity and were not satisfying its purpose. When he was on a leisure walk in 1904, Fleming had a thought provoking and path breaking idea of applying the Edison’s effect in solving the difficulty. It was soon proved by his assistants that the idea worked. Since this involved a slow to and fro motion of electric waves, this was called as oscillation valve. This idea which was patented by Fleming was the major reason for a wireless technology in the future. Though there were still more advancements needed for the vacuum tube, it was far more superior to the magnetic detectors and the coherers. In spite of all its advantages, the vacuum tubes experienced pit falls. It required a large amount of power, which was to be supplied by highly expensive batteries. To overcome these disadvantages, relatively cheaper devices were invented later. Two different patents were filed for the devices. The first patent was for Ferdinand Braun for a manganese oxide hydrated crystal and the other patent was for a carborundum crystal by H.Dunwoody.

The highly advanced vacuum tube 

Lee De Forest - Copyright:- Wikimedia Commons

With all the advancements and the advantages of the newly developed crystal detectors, people craved behind the vacuum tubes. The most crucial step for the development of vacuum tube was made by Lee de forest. His notable remark was that he held more than 300 patents. He worked on a wide range of wireless technologies. His father was a congregational minister. He was not supported by his parents. The invention of audion tube was his most known invention. The audion tube consisted of triple elements and its uniqueness was that the current was controlled by a grid. This was the invention that paved way for the radio. He initially worked on Fleming’s diode valve and then introduced a third electrode into it. In this three electrode device, the new electrode was placed between the anode and the cathode. This was supported by a grid like structure. Only by 1911, the vacuum tube was first used as an amplifier. Professor Lee de forest demonstrated a new idea to the telephone company, A.T & T. His new idea was building an amplifier by employing three audions. When he demonstrated, the efficiency was poor, but since they realized the potential of this, they adapted the experiment and made further advancements to rectify any blunders. Once the vacuum tube was used as an amplifier, people started to using it as an oscillator as well. But, soon the problem was in preventing oscillations in regard to the high value of the grid anode capacitance.

So that’s all about the story behind invention of vacuum tubes. We hope you have enjoyed the story and in the process gained really valuable insights and information as well. Wait for other stories in the series!



  1. Im doinn ma diploma in final year nw….plzz suggest me sum good nd best projects to ma email

  2. kuldip jadav

    can we make automatic side light in car, bike etc

  3. Hello fellows, Sorry but the develop or autdion tube (triode)is not the De Forest mind, because he never understod how its works,; Was an young and very smart teen named Edwin Howard Armstrong ( can you search at google,,,,) who discovered the Feedback or regeneration , when was a Columbia University student, but isn’t the unique thing. He design a complete system of FM radio broadcasting (1936)in use across of ww2 with convenience for the allies and at first HIFI Net in 1950 in Germany , super heterodyne receiver( developed in ww1 at France working for allies and patented in 1917 in US) and he regen(1912)which discover claims De forest in 1914 and win legal battle of 14 years, but scientific comm say Armstrong did… and superregenerative receiver 1922 ( in use today for very simple circuit thanks to the keyless cars opener radios remocons.Gretengs from Argentina