Introduction and function of tube
The basic electron tube generally has three poles, a cathode (K) for emitting electrons, an anode (A) for absorbing electrons emitted by the cathode, and a grid (G) for controlling the flow of electrons to the anode. The basic conditions are: the cathode itself must have considerable heat, and the cathode is divided into two types, one is the direct heating type, which emits electrons by the current directly heating the cathode through the cathode to emit electrons; the other is called the bypass type cathode, which The structure is generally a hollow metal tube, which is equipped with a filament wound into a spiral shape, and the voltage of the filament makes the filament heat, which causes the cathode to generate heat and emit electrons.Most of the daily use is now this kind of electron tube (as shown in the figure). The electrons emitted by the cathode pass through the gap between the gate wires to reach the anode.Since the gate is much closer to the cathode than the anode, changing the gate potential has a much greater impact on the anode current than changing the anode voltage. The amplification effect of the triode. In other words, the control effect of the gate voltage on the anode current. We use a parameter called transconductance (S) to represent. In addition, there is a parameter μ to describe the amplification factor of the electron tube, which means It shows how much the grid voltage controls the anode current than the anode voltage has more effect on the anode current.
In order to improve the amplification factor of the electron tube, an additional grid is added between the anode of the triode and the control grid called the curtain grid, and the quadrupole is formed. Since the curtain grid has a much higher positive voltage than the cathode, it is also A very powerful accelerating electrode, which makes the electrons quickly reach the anode at a higher speed, so that the control effect of the control grid becomes more significant. Therefore, it has a larger amplification factor than the triode. The acceleration effect of high-speed electrons hits the anode.The kinetic energy of these high-speed electrons is very large.The so-called secondary electrons will be hit from the anode.Some of these secondary electrons will be absorbed by the grid to form the grid current, which will increase the grid current. This will result in a drop in the curtain grid voltage, which will lead to a decrease in the anode current. For this reason, the amplification factor of the diode is limited.
In order to solve the above contradiction, a pair of collector-emitters connected to the cathode are added on both sides outside the grid of the quadrupole curtain. Since the collector and emitter have the same potential as the cathode, they have a repelling effect on the electrons, making the electrons pass through the curtain After the grid, under the action of the collector, it advances in a certain direction and forms a flat beam.The electron density of this flat electron beam is very large, thereby forming a low-pressure area.The secondary electrons hitting the anode are subjected to this low pressure. The repulsive effect of the zone is pushed back to the anode, which greatly reduces the curtain grid current, and the amplification ability of the electron tube is strengthened. This kind of electron tube is called a beam radiating quadrupole. High, and its anode area is large, allowing a large current to pass, so it is commonly used in power amplifiers as power amplification.
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