Types of Vacuum Tubes

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how vacuum tubes work

The vacuum tube, often known as the valve, is an interesting cleaning element that has made many significant technologies possible. Of course, this is a component that is used in several ways for different jobs.

All of such tubes mainly has an anode and a cathode in a vacuum setting. The appearance varies from small ceramic sized as a corn seed to one-meter or taller compact steel. Some locally available ones are made from glass or aluminum with a cylindrical shape. This article introduces the main types of vacuum tubes.

Different Types of Vacuum Tubes

1. Diode Vacuum Tubes

One of the simplest forms of vacuum tubes is the diode. As the name suggests it has two terminals including an anode and a cathode. Once the cathode is adequately heated, its electrons move from the surface because of the thermionic effect. If the cathode has a higher amount of electric potential and is applied on its anode end, the negatively charged electrons discharged from the cathode are attracted to the anode.

Diode Vacuum Tubes

Through the convection, the electric currents move in the direction of positive charges. Thus, it is always believed that the flow is from the anode terminal towards the cathode end. The reason is that negatively charged currents going in the same direction is equal to the positive charges flowing in the reverse direction.

The cathode end of vacuum tubes gets heated to emit electrons. At the time the anode has higher electric potential than the cathode terminal, the released electrons get attracted to it. During this time electric currents start flowing through convention from the positive end to the negative side. This happens even if the negatively charged electrons move from the negative end to the positive end.

2. Triode Vacuum Tubes

With this type of vacuum tube, the electric currents flow from the V+ having a high potential that has been applied on the anode end to the cathode’s ground potential. However, there is a valve that is still needed to control this flow. Triodes need a grid that is more like a third terminal between the cathode and the anode. This element has the potential of negative electric charges as the cathode that helps in controlling the movement of electrons between the terminals.

Triode Vacuum Tubes

If the grid has the lower electric potential I comparison to the cathode end, the electrons discharged by its cathode terminal become repelled will not easily go to the anode. If it has enough negative charges, its current gets blocked, attaining a similar effect that helps to close the valve available in the hydraulic circuits.

 But at the time the potential of the grid is the same as what is in the cathode, its current moves without obstruction from the anode to the cathode end. This brings a similar effect that fully opens the tube in that hydraulic circuit. In-between the negative grid currents control the current moving from the anode end to the cathode. The moment a voltage indicator is put to the grid, all the electric currents from the anode to the cathode will follow the signals applied on it. At this time it is worth noting that there is no current that can pass through the grid during the usual operations. As a negative grid as the cathode, it will repel the electrons thus restricting the flow of electric currents.

3. Tetrode Vacuum Tubes

The main idea behind the creation of the triode is related to the formation of the tetrode. It consists of a fourth electrode known as the screen located between the grid and the anode. The purpose of this additional component is to reduce the capacitance emitted from the features, the grid, and the anode.

Tetrode Vacuum Tubes

What is more, triodes have their grid and the anode placed close to each other and both work like a small-sized capacitor, which may cause unsteadiness and oscillations. This screen work as that for electrostatic between the anode and the cathode. However, this is possible if its voltage is higher than what the cathode and the grid have and at the same time is lower than what is in the anode. That means it reduces the inherent capacitance between the anode and the grid. The screen also is set to work in an ultra-linear structure by giving it some fraction of the output signal at the anode.

The screen in a tetrode is positive following where the cathode is at. Therefore, it can attract some amount of the emitted electrons from the cathode that can go to the anode. As a result, there will be a smaller current flow through it. This effect is used when configuring vacuum tubes to function with spread load or in ultra-linear modality.

The configuration is acquired by feeding some part of the output signal on the anode to the screen instead of putting on some fixed voltage onto it. The required percentage of output signal is usually delivered to the screen if it is connected to another tap from the output transformer. The flowing current via the screen yields a type of negative reaction. Even better, with the right proportion of anode signal the value of distortion falls minimally thus reducing power effectiveness. The optimum percentage that can be applied to this screen is determined by the specific vacuum tubes used. Most of the available designs of power amplifiers has this percentage set to about 43percent.

4. Pentode Vacuum Tubes

The introduction of pentodes led to the further advance of the tetrode. Here whenever electrons are emitted from the cathode to reach the anode chances are that they will have sufficient energy that can stimulate the emission of secondary electrons from the anode. However, the emitted electrons might cause instability and even oscillations when they reach the grid. There is the fifth electrode, the suppressor, that is normally used to prevent this emission electrons. This component is directly connected to its cathode, using a connection inside the vacuum tube or with an open connection between the matching pins.         

Pentode Vacuum Tubes

Finally, there are various types of vacuum tubes that occupy important aspects in various technological fields. The functioning principle is the same as that of hydraulic valves. Indeed, all this is possible thanks to the electron flow in the vacuum space.

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