1. Thermal electron emission
In electrotechnics, the orientation of current is this: the directional movement of electrons forms a current, so where does this electron come from? We know that in the theory of electrons, there is a "hot electron emission" phenomenon. It is said that among the metal atoms, the outermost electrons of the brand nucleus are less attracted by the nucleus, and some may be in the atom. Moving between, this is what we call free electrons. Although it can move and is less attracted to the nucleus, it is still not enough to leave the metal surface, but we also found that when the temperature increases, the speed of movement of these free electrons increases, the kinetic energy will increase, when its kinetic energy is greater than When the escaping force is needed, the electrons will overcome the gravity of the atomic nucleus and fly away from the metal surface. This is the phenomenon of "hot electron emission".
Second, the cathode of the electron tube
1. Types of cathode
The electron-emitting objects in the electron tube are called cathodes. There were not many kinds of cathodes in the early electron tubes. Nowadays, due to the advancement of technology, the types of cathodes have become more and more, but carbonized cathodes, oxide cathodes, tungsten cathodes, etc. still occupy the mainstream status.
Tungsten cathode: As the name implies, this is a cathode made of tungsten wire. It needs to emit more electrons at about 2300 degrees Celsius. Obviously, energy consumption will be very large to reach this temperature, but tungsten is a very stable element, so It has good stability and long life, so it is mostly used in high-power launch tubes.
Carbonized cathode: It is a cathode made of carbon and thorium oxide coated on tungsten wire. It emits electrons at about 1700 degrees Celsius. Compared with tungsten cathode, its energy consumption is low, but its stability is not as good as tungsten cathode and cannot work High screen pressure, so it is mostly used for medium power launch tube.
Oxide cathode: It is a cathode made of strontium, calcium, barium and other oxides coated on nickel wire. It can emit more electrons at about 800 degrees Celsius. This kind of cathode has a much larger emission current than the previous two types. However, at the same time, it has the disadvantages of unstable operation, inability to work at high screen voltage, and damage by positive ion impact, so it is mostly used in receiving tubes or as low-power electron tubes. The electron tubes used by enthusiasts are mostly oxide cathode electron tubes.
2. Direct-heating cathode and inter-heating cathode
In addition to the different materials used for the cathode of the electron tube, there are different ways of heating. The figure on the left has vividly depicted the difference between these two methods.
Direct-heating cathode: The cathode is the heating filament. Obviously, to work stably, it is only suitable for DC power supply. In the past, many machines were powered by dry batteries (A and B), because if AC power is used, there will be a large Hum.
Intermediate-heat cathode: The cathode and the filament are separated. It uses a heated filament and uses the high temperature of the filament to bake the cathode to complete the electron emission task. Generally, the cathode is made into a cylindrical shape, and the filament is placed in the tube, so that the heating efficiency is high and the heating is uniform.
3. Diode
A diode is of course a tube with only two electrodes, a cathode and a screen (anode). It is installed in a high vacuum glass or metal tube. At this time, the cathode is used to emit electrons, and the anode is used to collect electrons.
The diode has a very special feature, that is, when the anode voltage is low, the cathode emits electrons continuously, but at this time, except for few electrons will reach the anode, more electrons are gathered around the cathode, when the anode When the voltage is high enough, these electrons will all fly to the anode (screen electrode), and the screen current is also the largest. There is no screen flow, which is the unidirectional conductivity of the diode. Because of this, it can be used for AC rectification and AC signal detection.
Four, triode
The triode is basically an additional electrode in the diode, that is, a grid is added between the cathode and the anode to form the triode. In the diode, we found that changing the anode voltage can change the screen current, but in the triode, due to the grid It is closer to the cathode than the anode. At this time, you will find that even if the voltage of the gate and the anode are changed the same, the influence of the grid on the screen current is much greater than the influence of the anode on the screen current. , Will cause a great change in the screen current, just as a small change in the base voltage of the transistor will cause a great change in the collector current. For the transistor, this shows that the base of the transistor controls the collector. This role The size (ratio) is the amplifying ability (β value) of the transistor. Similarly, the control voltage of the gate voltage of the three-stage tube to the screen current has a standard term: transconductance, which is also a very important parameter of the triode .
Five, quadrupole, pentode
1. Quadrupole
In response to the problem that the transistor amplification factor is not large enough, the capacitance between the screen grid is large, and the tube is not suitable for high-frequency circuit applications, people have basically invented the quadrupole based on the triode tube, and the specific structure is between the grid and the screen An electronic pole is added between them, called the curtain grid. It is usually made of metal wire. The advantage is that the capacitance between the screen grid is reduced and the magnification is increased (the grid controls the screen flow).
In order to solve the problem that the screen flow of the quadrupole is not large enough, people have invented the beam-emitting diode. Although the number of electrodes has not increased, the arrangement and shape of the internal electrodes have been changed, so that the beam-emitting diode has a screen. The characteristics of large current and small curtain current can be used in occasions with large power output.
2. Pentode
The quadrupole also has some fatal shortcomings when working, such as secondary electron emission, and the screen current is therefore reduced in certain ranges, so in order to prevent this phenomenon, the designer added another between the grid and the screen Control grid, this becomes a pentode, it solves the problem of secondary electron emission of the tetrode better.
The transconductance of a pentode is similar to that of a triode, and its internal resistance is large, and its amplification factor can reach thousands of times. The remote cut-off pentode (frequency converter) in the pentode is an alternative pentode. Its grid structure and winding method are more particular. The finished tube is mostly used in the intermediate frequency amplification with automatic volume control in the radio. Circuit.
6. Composite pipes and others
A compound tube refers to a general term for an electronic tube that encapsulates more than one tube function tube core in a housing. It can be a bipolar tube, a double triode, etc.
The same concept of compounding is also introduced into other electron tubes, such as the multi-grid electron tubes commonly used in super-heterodyne radio frequency conversion circuits, that is, electron tubes with two, three or even more than four grids in one electron tube.
In addition, as a branch of the electron tube, there are also picture tubes (cat's eyes) for display, and the change of graphics and colors are often used to display the size of the circuit signal level and volume. Of course, there are glow discharge tubes for voltage regulation. and many more.
In electrotechnics, the orientation of current is this: the directional movement of electrons forms a current, so where does this electron come from? We know that in the theory of electrons, there is a "hot electron emission" phenomenon. It is said that among the metal atoms, the outermost electrons of the brand nucleus are less attracted by the nucleus, and some may be in the atom. Moving between, this is what we call free electrons. Although it can move and is less attracted to the nucleus, it is still not enough to leave the metal surface, but we also found that when the temperature increases, the speed of movement of these free electrons increases, the kinetic energy will increase, when its kinetic energy is greater than When the escaping force is needed, the electrons will overcome the gravity of the atomic nucleus and fly away from the metal surface. This is the phenomenon of "hot electron emission".
Second, the cathode of the electron tube
1. Types of cathode
The electron-emitting objects in the electron tube are called cathodes. There were not many kinds of cathodes in the early electron tubes. Nowadays, due to the advancement of technology, the types of cathodes have become more and more, but carbonized cathodes, oxide cathodes, tungsten cathodes, etc. still occupy the mainstream status.
Tungsten cathode: As the name implies, this is a cathode made of tungsten wire. It needs to emit more electrons at about 2300 degrees Celsius. Obviously, energy consumption will be very large to reach this temperature, but tungsten is a very stable element, so It has good stability and long life, so it is mostly used in high-power launch tubes.
Carbonized cathode: It is a cathode made of carbon and thorium oxide coated on tungsten wire. It emits electrons at about 1700 degrees Celsius. Compared with tungsten cathode, its energy consumption is low, but its stability is not as good as tungsten cathode and cannot work High screen pressure, so it is mostly used for medium power launch tube.
Oxide cathode: It is a cathode made of strontium, calcium, barium and other oxides coated on nickel wire. It can emit more electrons at about 800 degrees Celsius. This kind of cathode has a much larger emission current than the previous two types. However, at the same time, it has the disadvantages of unstable operation, inability to work at high screen voltage, and damage by positive ion impact, so it is mostly used in receiving tubes or as low-power electron tubes. The electron tubes used by enthusiasts are mostly oxide cathode electron tubes.
2. Direct-heating cathode and inter-heating cathode
In addition to the different materials used for the cathode of the electron tube, there are different ways of heating. The figure on the left has vividly depicted the difference between these two methods.
Direct-heating cathode: The cathode is the heating filament. Obviously, to work stably, it is only suitable for DC power supply. In the past, many machines were powered by dry batteries (A and B), because if AC power is used, there will be a large Hum.
Intermediate-heat cathode: The cathode and the filament are separated. It uses a heated filament and uses the high temperature of the filament to bake the cathode to complete the electron emission task. Generally, the cathode is made into a cylindrical shape, and the filament is placed in the tube, so that the heating efficiency is high and the heating is uniform.
3. Diode
A diode is of course a tube with only two electrodes, a cathode and a screen (anode). It is installed in a high vacuum glass or metal tube. At this time, the cathode is used to emit electrons, and the anode is used to collect electrons.
The diode has a very special feature, that is, when the anode voltage is low, the cathode emits electrons continuously, but at this time, except for few electrons will reach the anode, more electrons are gathered around the cathode, when the anode When the voltage is high enough, these electrons will all fly to the anode (screen electrode), and the screen current is also the largest. There is no screen flow, which is the unidirectional conductivity of the diode. Because of this, it can be used for AC rectification and AC signal detection.
Four, triode
The triode is basically an additional electrode in the diode, that is, a grid is added between the cathode and the anode to form the triode. In the diode, we found that changing the anode voltage can change the screen current, but in the triode, due to the grid It is closer to the cathode than the anode. At this time, you will find that even if the voltage of the gate and the anode are changed the same, the influence of the grid on the screen current is much greater than the influence of the anode on the screen current. , Will cause a great change in the screen current, just as a small change in the base voltage of the transistor will cause a great change in the collector current. For the transistor, this shows that the base of the transistor controls the collector. This role The size (ratio) is the amplifying ability (β value) of the transistor. Similarly, the control voltage of the gate voltage of the three-stage tube to the screen current has a standard term: transconductance, which is also a very important parameter of the triode .
Five, quadrupole, pentode
1. Quadrupole
In response to the problem that the transistor amplification factor is not large enough, the capacitance between the screen grid is large, and the tube is not suitable for high-frequency circuit applications, people have basically invented the quadrupole based on the triode tube, and the specific structure is between the grid and the screen An electronic pole is added between them, called the curtain grid. It is usually made of metal wire. The advantage is that the capacitance between the screen grid is reduced and the magnification is increased (the grid controls the screen flow).
In order to solve the problem that the screen flow of the quadrupole is not large enough, people have invented the beam-emitting diode. Although the number of electrodes has not increased, the arrangement and shape of the internal electrodes have been changed, so that the beam-emitting diode has a screen. The characteristics of large current and small curtain current can be used in occasions with large power output.
2. Pentode
The quadrupole also has some fatal shortcomings when working, such as secondary electron emission, and the screen current is therefore reduced in certain ranges, so in order to prevent this phenomenon, the designer added another between the grid and the screen Control grid, this becomes a pentode, it solves the problem of secondary electron emission of the tetrode better.
The transconductance of a pentode is similar to that of a triode, and its internal resistance is large, and its amplification factor can reach thousands of times. The remote cut-off pentode (frequency converter) in the pentode is an alternative pentode. Its grid structure and winding method are more particular. The finished tube is mostly used in the intermediate frequency amplification with automatic volume control in the radio. Circuit.
6. Composite pipes and others
A compound tube refers to a general term for an electronic tube that encapsulates more than one tube function tube core in a housing. It can be a bipolar tube, a double triode, etc.
The same concept of compounding is also introduced into other electron tubes, such as the multi-grid electron tubes commonly used in super-heterodyne radio frequency conversion circuits, that is, electron tubes with two, three or even more than four grids in one electron tube.
In addition, as a branch of the electron tube, there are also picture tubes (cat's eyes) for display, and the change of graphics and colors are often used to display the size of the circuit signal level and volume. Of course, there are glow discharge tubes for voltage regulation. and many more.
Toys Stress Relief Phone Stand which can release your pressure.
Toys Stress Relief Phone Stand
Toys Stress Relief Phone Stand,Stress Balls,Stress Relief Balls,Personalised Stress Balls
Reteck Storage Device Co., Ltd. , https://www.reteck.com