What is a Vacuum Tube?

"Vacuum Tube" (Vacuum Tube) represents the vacuum inside the glass bottle to facilitate the flow of free electrons, and can also effectively reduce the oxidation loss of the filament. Vacuum tubes are widely used in every corner of life.

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"Vacuum Tube" (Vacuum Tube) represents the vacuum inside the glass bottle to facilitate the flow of free electrons, and can also effectively reduce the oxidation loss of the filament. Vacuum tubes are widely used in every corner of life.

Chinese name

Vacuum tube

Foreign name

Vacuum Tube

Principle

Flow of free electrons

Application area

Electronic physics

It all started with electronics.

Triode is the most basic vacuum tube

Diodes, triodes, and pentodes literally represent the number of basic "poles" inside a vacuum tube. The vacuum tube has three basic poles. The first is the "cathode" (represented by K): The cathode is of course negative. It is the place where the electron flow is released. It can be a metal plate or the filament itself. When When the filament heats the metal plate, the electrons will be released and scattered in the small vacuum glass bottle. The second pole is the "Plate" (represented by P), which is basically the metal plate on the outermost part of the vacuum tube. The dark gray or black metal plate on the outermost layer of the vacuum tube is usually the screen electrode. The screen electrode is connected to a positive voltage, which is responsible for attracting the electrons emitted from the cathode (remember? Using the principle of opposite phase attraction) as the end point of the free travel of electrons. The third pole is a grid (represented by G). From a structural point of view, it looks like a thin coil, just like a fence. It is fixed between the cathode and the screen. The electron flow must pass through the grid. When the voltage is applied to the screen, the flow of electrons can be controlled by applying a voltage between the grids. It acts like a faucet, with the functions of circulation and blocking.

The vacuum tube light has three poles. Of course, it is not perfect. Therefore, the subsequent vacuum tube has been continuously improved, and there have been many improvements in the structure to match different magnification methods (such as super linear connection, etc.). The content has left this article and will not be described in detail for the time being.

The engine must have fuel to run, and the action power of the vacuum tube is electric energy. The most important electrode of a vacuum tube is the cathode, which is responsible for releasing electrons as the basis of all actions. The earliest vacuum tubes used the filament directly as a cathode because of its simple structure and theory. In other words, when the filament was lit, as the filament temperature increased, electrons were released from the filament and passed through the grid to the screen electrode. This type of vacuum tube is called a "direct heating vacuum tube". The protagonist 300B of this topic belongs to this type of vacuum tube. Compared with other modern five-pole vacuum tubes, the 300B has a simple structure, good performance, and low output power.

Vacuum tube

Now, let's take a closer look at the simplest working principle of a vacuum tube. To summarize, the vacuum tube has several poles, from the innermost layer to the outermost layer: the filament, the cathode, the grid, and the screen. After disassembling a vacuum tube, it is drawn in the drawing. It can be seen from the figure that when the filament is lit, the filament temperature gradually increases. Although it is in a vacuum state, the filament temperature is transmitted to the cathode metal plate by radiant heat. When the temperature of the cathode metal plate reaches the temperature at which the electrons are released, the electrons will fly away from the metal plate and

Vacuum tube according to heating method

Vacuum tubes can be divided into two categories, namely direct heating and indirect heating.

Directly heated vacuum tubes were born earlier. It has a fatal disadvantage that the cathode is easily changed by the temperature of the filament. When the filament voltage fluctuates, or when the filament is supplied with alternating current, the cathode appears in an unstable state.

The work of indirectly heated vacuum tubes is relatively stable. Because the volume and heat storage of the metal sleeve is much larger than that of the traditional filament, even if the temperature of the filament temporarily changes, or even temporarily stops heating for a few seconds, the temperature change of the metal plate is limited. After that, the main reason why it can sing for more than ten seconds is because the power supply has a large capacity capacitor and the internal power is not discharged.

Vacuum tubes are classified by container structure

Most commercially available vacuum tubes have glass walls. The military and other special types are made of metal.

Divided by structure and application of vacuum tube

Vacuum tubes can be divided into many types such as diodes, triodes, tetrodes, tetrode beam tubes, pentodes and composite tubes. Classification and common models according to use:

Composite pipe

Pentode

Rectifier diodes: 12F, 81, 35W4, 25M-K15, 5MK9

Dual diodes for rectification: 80, 5Z3, 5AR4, 5U4, 6X4, 5Y3, 83, 82

Chirped diodes: 6AL5, EAA91, 6H6

Tuning indicator tube: 6E5, EM80

Triode for electric amplifier: 6C4

Double triode for electric amplifier: 12AX7, 12AU7, 12AT7, 12BH7A, 6DJ8, 6SN7

Transistors for power amplification: 45, WE300B, 2A3, 211, 845, 8045G

Double triode for power amplification: 6336A, 6080

Collective emitter tetrode for power amplification: UY-807, KT88, 6L6, 6V6

Electron amplifier pentodes: 6AU6, 6BA6, 6BD6, 6267, 6SJ7

Power amplifier pentode: 6F6, 6CA7, 6BQ5, 6550, 6AR5, 42, 30A5, 50C5

Seven-pole tube for frequency conversion: 6SA7, 6BE6

Transmitting Transistor: 3-500Z, 3-1000Z

Transmitting Transistor: 4CX250B

Transmitting pentode: 6146B, S2001A

Side-heated double triode small signal tube: 6922, ECC88, 6DJ8

Directly heated triode power tube