Principle of electronic tube construction

Introduction

The following discussion is limited to vacuum tubes

Diode:

Consider a heated metal plate. When its temperature reaches above 800 degrees Celsius, it will form an accelerated movement of electrons, so that it can escape from the metal plate itself and escape to the space outside the metal surface. If a positive voltage of tens to tens of thousands of volts is applied to this space (in the picture tube mentioned above, a high voltage of 7000-27000 volts is applied to the anode), these electrons will be attracted to fly forward. The voltage pole flows through the power supply to form a loop current.

diode

The metal plate (cathode), heating source (filament), and positive voltage plate (anode) are packaged in a suitable shell, that is, the glass (or metal, ceramic) package shell mentioned above, and then pumped into a vacuum, It is an electronic diode.

What needs to be explained is that due to the manufacturing process, the adhesion of impurities and the material itself, a small amount of residual gas will remain in the tube, and the finished tube is coated with a layer of getter. The getter generally uses nitrogen-doped evaporative zirconium aluminum or zirconium vanadium materials. Except for special purposes (such as ultra-high frequency and high-voltage rectification, etc.), in order to facilitate the use and increase the uniformity, all are two diodes, or two poles and three poles, or three poles, three poles, and two poles and five poles. Inside the shell, this is the composite tube. [6]

Transistor

The structure of the diode determines its unidirectional conductivity. When a pole with an appropriate voltage is added between the cathode and the anode, this voltage will change the surface potential of the cathode, thereby affecting the cathodic hot electrons flying to the anode. Quantity, this is the modulating pole, which is usually made of a spiral grid made of metal wire, so it is also called a grid. This is the valve function. From this it can be known that when the amplified signal voltage is applied between the grid and the cathode, its change will inevitably cause a corresponding change in the anode current, and since the anode voltage is much higher than the cathode, the grid The slight voltage change between the cathodes can also cause the anode to produce a corresponding voltage change of several tens to hundreds of times. This is the principle of the triode amplifying the voltage triode signal. [7]

tetrode

The purely tetrode has only appeared as a verification tube in the history of the development of electronic tubes and has not been put into practical use. More than half of the commercial power amplifiers use beam tetrodes. All beam tetrodes are power tubes, and the requirement for power tubes is to generate as large anode current as possible. The beam tetrode has made some special arrangements on the electrode structure, so that it can form a larger anode current than other power tubes while maintaining the same volume as other power tubes.

Several structural features of beam tetrode:

1. The cathode is elliptical, which increases the effective emission area of the cathode, thereby increasing the emission of thermionic electrons.

2. Like the triode, a screen grid is added between the suppression grid and the anode. The function is mentioned above.

3. A pair of bow-shaped metal plates are added between the screen grid and the anode (when it comes to the point, pay attention to the following expression), this is the cluster screen. The clustering screen is connected to the cathode in the tube, that is, it is equipotential with the cathode. It forces the electron flow that has crossed the screen grid to be beamed toward the anode along the opening direction of the arch-shaped metal plate.