What Is A Vacuum Tube and How Does It Work

Ⅰ. What is a vacuum tube?

Vacuum tubes are basically valves that control the flow of electrons. It looks a bit like a light bulb (often made of glass) that has been evacuated to a near-vacuum inside. Inside this near-vacuum sealed chamber are two main pieces of equipment. One is called the heating electrode, which is located in the center of the tube and emits an orange light when the tube is working; the other is composed of the cathode, metal grid and metal plate (also known as the anode). The anode plate is the largest metal component seen in the tube. All elements are positioned and separated with mica and ceramic spacers.

The vacuum tube is the source of energy for the solar water heater to generate hot water, and it is also a key component of the solar water heater, so the vacuum tube is called the "heart" of the solar water heater. Vacuum tubes are as important in a solar water heater as the engine is in a car.

Ⅱ. The development of vacuum tubes

In 1883, the famous inventor Thomas Edison observed a strange phenomenon when he was testing the life of the filament: the copper wire was not connected to the electrode, but it could still generate current. Edison named it the "Edison Effect".

In 1896, Italian Guglielmo Marconi successfully obtained the world's first wireless telegraph system patent, thus bringing mankind into the era of wireless communication.

In 1874, German scientist Karl Ferdinand Braun discovered that some natural ores (metal sulfides) have the characteristic of one-way conduction of electric current, which can be used for rectification (conversion of alternating current into direct current).

In 1894, Jagadish Chandra Bose, a British Indian physicist based on the discovery of Karl Ferdinand Braun, used the unidirectional conductivity of galena (lead sulfide) to make the world's first geophone—the ore geophone.

In 1900, American Greenleaf Whittier Pickard successfully manufactured the world's first ore radio based on the ore detector. This laid the foundation for the rapid popularization of radio broadcasting later.

In 1904, Fleming invented the world's first vacuum electron diode. At that time, this diode was also known as the "Fleming valve". The emergence of diodes solves the detection and rectification needs.

In 1906, De Forest Lee cleverly added a grid to the vacuum diode and invented the vacuum triode. Its invention is a milestone event in the field of electronics industry. The triode integrates the three functions of detection, amplification and oscillation, laying the foundation for the development of electronic technology.

From 1912 to 1920, Western Electric developed a practical spherical electronic triode. People call it an "onion" tube.

In 1924, Radio Corporation of America developed a triode vacuum tube with higher efficiency. This classical pipe was widely used in World War I.

In 1919, Schottky of Germany proposed the idea of adding a curtain grid between the grid and the positive electrode. This idea was realized in 1926 by Rand in England. This is the later tetrode. Later, Holst and Telegen in the Netherlands invented the pentode.

In 1940, computer technology research entered a climax. It was found that the one-way conduction characteristic of the tube can be used to design some logic circuits (such as AND gate circuits, OR gate circuits). So, they began to introduce the electronic tube into the computer field.

In 1946, Eckert, an engineer at the University of Pennsylvania, and physicist Mauchly and others jointly developed the first general-purpose electronic computer in the true sense-ENIAC.

From 1940 to 1950, the development of electronic tubes reached its climax. However, with the advancement of technology, it has been found that electronic tubes can no longer meet the needs of product design. On the one hand, the electronic tube is easily damaged and has a high failure rate; on the other hand, the electronic tube needs to be heated to use, and a lot of energy is wasted on heating, which also brings extremely high power consumption. Therefore, people began to look for and develop alternatives to electronic tubes.

On June 30, 1948, the Bell Telephone Research Institute of the United States announced that it had made the world's first transistor. Its inventors Shockley, Bardeen and Bratton were all engaged in theoretical research on solid physics in the 1930s and 1940s. After repeated failed experiments, they finally achieved a major success on December 23, 1947 and invented the transistor. The emergence of transistors is a great leap forward for human beings in electronics.

Ⅲ. The structure of the vacuum tubes

1. Shell: It is used to form a vacuum area and fix the internal structure.

2. Anode: This electrode in a vacuum tube or valve has a high potential that attracts electrons from the cathode.

3. Cathode: This is the electrode that is heated and emits electrons.

4. Stem: It supports the electrodes in the tube and leads the electrodes out of the tube.

5. Base pin: The base pin is installed on the pin, which is used to fix the lamp tube and connect it with the external circuit.

6. Grid: This is the valve electrode with variable potential to control the flow of electrons between the cathode and anode. In some vacuum tubes, more grids are used to improve performance in various ways.

7. Mica sheet: It is used to fix the electrode position, maintain the relative position between electrodes, and prevent vibration damage.

8. Filament: Most valves are now indirectly heated, that is, the filament is not connected to the cathode. The filament heats the cathode, which then emits electrons. Early valves were directly heated and a filament was used to emit electrons. However, this limits how the valve can be used. Having a cathode with indirect heating allows the cathode to be operated at a potential above ground and also allows many filaments to be run in parallel in a single device.

Ⅳ. The working principle of the vacuum tube

Vacuum tubes contain two or more electrodes separated by ionized gas or low-pressure vacuum. It goes from one electrode to the other through the tube. Its operation depends on the basis of the generation and transfer of electrons. The cathode is the source of electrons, usually a metal electrode from which the cathode emits. Magnetic fields, electric fields, or both are used to control the movement of electrons emitted by the cathode. Vacuum tubes can generate magnetic fields through permanent magnets or electromagnets outside the tube. In simple form, the positive pole attracts and accelerates electrons, and the negative pole repels and slows electrons down.

Ⅴ. The type of vacuum tubes

1. Classified by the number of electrodes

Vacuum tubes can be divided into voltage amplifier tubes, triodes, tetrodes, pentodes, hexodes, heptodes, octodes, nine-poles and composite tubes. Electric tubes with more than three electrodes are also called multi-electrode tubes or multi-gate tubes.

(1) Diode vacuum tube

A diode is the simplest form of a vacuum tube. It contains two terminals, anode and cathode. When the cathode is sufficiently heated, its electrons are transferred from the surface due to the thermionic effect. If the cathode contains a higher potential and is applied to the anode, the cathode emits negatively charged electrons, which are attracted to the anode. The current then flows in the direction of the positive charge by convection.

(2) Triode vacuum tube

It is a semiconductor device that controls electric current. Its function is to amplify the weak signal into an electrical signal with a larger amplitude value, and it is also used as a non-contact switch. The triode is one of the basic components of semiconductors and has the function of current amplification. It is the core component of electronic circuits. The triode is made of two PN junctions that are very close to each other on a semiconductor substrate. The two PN junctions divide the whole semiconductor into three parts. The middle part is the base region, and the two sides are the emitter region and the collector region. There are two arrangements: PNP and NPN.

(3) Quadrupole vacuum tube

The original purpose of creating the triode was related to the introduction of the quadrupole vacuum tube. Between the anode and the grid, the tetrode contains a fourth electrode, called the screen. The main purpose of this advanced component is to short out the capacitance created by the anode and gate. The grid and anode work like small capacitors in a triode. Because they are very close to each other, this can cause instability and oscillations. If the shield consists of a higher voltage compared to the cathode, but a lower voltage compared to the anode, it reduces the grid and anode's inherent capacitance.

2. Classified by the heating method of the cathode

Vacuum tubes can be divided into direct-heated cathode electron tubes (the current passes directly through the cathode to achieve thermionic emission state) and side-heated cathode electron tubes (the cathode is heated by the filament next to the cathode).

3. Classified by cooling method

Vacuum tubes are divided into water-cooled tubes, air-cooled tubes and naturally cooled wgyb tubes.

4. Classified by purpose

Vacuum tubes can be divided into voltage amplifier tubes, power tubes, gas-filled tubes, thyratrons, ignition tubes, frequency mixing or frequency conversion tubes, rectifier tubes, oscillation tubes, detector tubes, tuning indicator tubes, and voltage regulator tubes.

5. Classified by shielding method

Vacuum tubes can be divided into sharp cutoff shielded electron tubes and remote cutoff shielded electron tubes.

6. Classified by shape

Vacuum tubes are divided into ST tubes, GT tubes, G-type tubes, metal porcelain tubes, MT tubes, tower tubes, pencil-shaped tubes, etc.

7. Classified by internal structure

Vacuum tubes can be divided into single diodes, diodes, double diode triodes, double diodes, single triodes, power pentodes, beam tetrodes, beam pentodes, double monoodes and other types.

Ⅵ. The advantages and disadvantages of vacuum tubes

1. Advantages

(1) Tolerance to overload: Vacuum tubes are generally more able to withstand momentary overloads or overvoltages than transistors, which makes them more reliable in some high-load environments.

(2) Wide operating temperature range: Vacuum tubes can work normally in a relatively wide temperature range, which makes them have certain advantages in applications in extreme environments.

(3) High power and high frequency characteristics: Vacuum tubes can handle high power and high frequency signals, making them very useful in applications such as broadcasting and radar that require high power amplification and frequency modulation.

(4) Sound quality and audio applications: In audio amplifiers, some music lovers believe that vacuum tubes can produce warmer, more natural sound quality. Therefore it is popular in some audio applications.

2. Disadvantages

(1) Lifespan and reliability: Since vacuum tubes involve complex mechanisms such as electron emission and space charge effects inside, they are relatively less stable and reliable than transistors, and are prone to failure.

(2) Sensitivity: Vacuum tubes are sensitive to mechanical vibration and shock, which may cause problems in some special environments.

(3) Volume and weight: Vacuum tubes are usually large and heavy, which limits the compactness and portability of the device. By comparison, transistors and integrated circuits are smaller and lighter.

(4) Manufacturing and maintenance costs: Since the manufacture of vacuum tubes involves more complex processes, as well as the manufacture of key components such as cathodes and vacuum seals, its manufacturing and maintenance costs are relatively high.

(5) Energy consumption: The vacuum tube needs to heat the cathode to make it work. This results in higher power dissipation and lower efficiency compared to later solid-state devices.

Ⅶ. Vacuum tube amplification principle

The working principle of the vacuum tube amplifier is to use the characteristics of electron emission and electron flow to amplify the input signal to a higher level. As electrons flow through the vacuum tube, they interact with the anode of the tube, creating an electric current. This current can be harnessed by the amplifier's output circuitry to generate higher voltages and currents.

The advantage of a vacuum tube amplifier is that it can produce very high gain, which makes it ideal for amplifying weak signals. Additionally, a vacuum tube amplifier is also very linear, which means it produces a very accurate output signal without any distortion. However, vacuum tube amplifiers also have some disadvantages. For one thing, they're very large and bulky, and require a lot of power. On the other hand, they require the use of high-quality materials and manufacturing processes, so they are expensive.

Ⅷ. How to identify the vacuum tubes?

The vacuum tube is the core component of the solar water heater, and is known as the "heart" of the solar water heater. The quality of the vacuum tube directly affects the service life and performance of the solar water heater. Here are a few ways to identify vacuum tubes

1. With the naked eye, the color of the inner tube of the vacuum tube is dark red, indicating that its metal bottom layer is copper. This kind of vacuum tube can also work normally under severe cold conditions, and hot water can be produced as usual at -30°C.

2. There are currently three best vacuum tubes on the market: high temperature tubes, high efficiency tubes, and alpine tubes. The film layer of the high-temperature tube is longer than that of the ordinary tube (about 1 cm from the nozzle), and the tube is resistant to high temperature and has strong attenuation resistance. The film layer will not age, fall off and change color under the high temperature air drying state of 400 ℃. The film layer of the high-efficiency tube is about 2.5cm away from the nozzle. This tube has less heat loss, quick heating and high thermal efficiency. The high-cold tube has the advantages of high thermal efficiency and fast temperature rise of the high-efficiency tube, and at the same time, the heat loss is less, and hot water is produced as usual under the condition of -30°C. Consumers can choose different vacuum tubes according to different regions.

3. The appearance of high-quality vacuum tubes has the following characteristics:

(1) The baked mirror surface is complete, bright and clean, without blackening.

(2) The surface is smooth and clean; the tube body has no spots, no air lines, no scratches, and no scratches (this phenomenon will affect the heat collection efficiency and appearance).

(3) The color of the film layer is mainly blue and black, and the overall color difference is small. But black does not mean that the vacuum tube is of good quality, because some manufacturers often make the film layer pure black in order to cover up variegated colors. In fact, it is inevitable that there is a certain error in the color of the vacuum tube, which does not affect the heat collection efficiency of the vacuum tube.