How Vacuum Tubes Work - Triode Control Grid - Anode Voltage - Anodic Current

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A TRIODE is an electronic amplifying device belonging to the vacuum tube family.
In electronics, a VACUUM TUBE is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
There are many types of vacuum tubes depending on their use. They are essentially used for a number of fundamental electronic functions such as SIGNAL AMPLIFICATION and CURRENT RECTIFICATION.
In the Anglo-Saxon Countries the triode is simply called “valve”, since it allows to vary the current that passes through it. Very often to explain the basic principle of its operation, the triode is compared to a tap that control the release of a liquid or gas.
The triode was born as a natural evolution of the diode.
As we already explained in our previous video, the function of a diode is to allow the flow of electric current in one direction and virtually block it in the opposite direction. The diode is in fact mainly composed of two electrodes called ANODE and CATHODE. The electron flow conventionally goes from the chatode to the anode following this direction. Opposite polarization of the diode will oppose a virtually infinite resistance. The diode blocks the current reducing it to zero.
Unlike the diode, the TRIODE (as the name suggests) is provided with a third electrode placed between the CATHODE and the ANODE called: GRID. All these elements are placed inside a tube in which a vacuum has been created, which means that all the air and other gases have been removed.
For a triode to actually work, it is necessary to create a STRONG POTENTIAL DIFFERENCE between its anode and cathode. For this reason the CATHODE is heated by a separate current flowing through a thin metal filament, in order to emit electrons via thermionic emission.
The GRID usually consists of a cylindrical screen or helix of fine wire surrounding but never touching the cathode. The grid acts like a gate for the electrons, controlling the current flow and thus allowing signal amplification.
Around the grid is placed the ANODE which receives the electrons emitted by the cathode.
This is a fairly simplified representation of the triode (image above). Which means that only the basic elements of the tube are shown, as we can also notice in its symbol, where the cathode and the anode are separated by the grid, which is represented by this dashed line.
As in the diode, the anode collects the electrons emitted by the cathode, which are not hindered by the grid, since they can easily pass through its coils.
However, the grid can significantly influence the movement of the electrons towards the anode, if there’s an electric potential difference between the grid and the cathode. Basically, when there’s no voltage on the grid, the current between the cathode and anode will be at its maximum. On the other hand, a less negative, or positive voltage on the grid will allow more electrons through. Let’s see how...

Видео How Vacuum Tubes Work - Triode Control Grid - Anode Voltage - Anodic Current канала JAES Company