Tube is working by hot electron emission, the electrode is called electron tube cathode emitting electrons, an electron tube is the "heart" section. Fans need to understand the main properties and characteristics of the cathode.
A directly heated cathode of indirectly heated cathode
There are directly heated cathode and an indirectly heated cathode tube heating two kinds of ways. Directly heated cathode tube is designed for battery-powered, i.e. the cathode filament, filament heating and therefore only suitable for DC power supply, when an AC-powered - will have a greater hum under normal circumstances.
An indirectly heated cathode and filament are separate from the cathode formed in a cylindrical shape, filament disposed cylinder center, the use of filament heating to the high temperature baking of the cathode, the cathode to a sufficient temperature to emit electrons. An indirectly heated cathode high efficiency heat evenly. Since the indirectly heated cathode and filament are separate, so that no AC supply hum. An indirectly heated cathode DC power supply may be employed.
Second, the type of the cathode
In the large family of electron tubes, cathode species, are dominant tungsten cathode, cathode carbide, oxide cathode three kinds.
1. tungsten cathode is a cathode made of metal tungsten. The tungsten cathode is the first cathode in the electronic tube. The advantage is that the stability is good, the life is long, and the emission performance is not applied to the tube of the high anode voltage due to the impact of the positive ion generated by the residual gas in the tube. The disadvantage is that in order to transmit enough electrons needed to reach the temperature 2300 deg.] C, to reach such a temperature, the heating current is large, high energy consumption, it is often used in high power transmitting tube.
2. Cathode carbide coated carbon cathode made of thorium oxide and the tungsten wire, around 1700 ℃ sufficient electron emission can be compared with the tungsten cathode heating current, low energy consumption, but not as good as the stability of tungsten a cathode, and a lower operating pressure screen, so the power used for the launch tube.
3. The oxide cathode strontium, calcium, and barium oxide coated on a cathode made of nickel wire, a temperature of about 800 deg.] C can be sufficient electron emission, and the emission current is much larger than the cathode of tungsten carbide and a cathode, it the cathode is the highest one of the three emission efficiency, low power for multiple tubes. In addition, it has a strong pulse emission characteristics. When coupled between the cathode plate and the duty factor of the pulse voltage is larger, a large pulse emission current obtained, which is specific to the performance of the oxide cathode. It is also widely used such a cathode tube operating pulse current (SCR) of.
Disadvantage is the poor stability of the oxide cathode, a lower operating pressure screen, positive ions susceptible to impact damage, known as cathode "poisoned." The so-called "poisoning" refers to the work function of the cathode of the cathode increases in harmful action of gas emission performance degradation phenomena. When the filament voltage is insufficient, when the cathode temperature is too low, the oxide cathode poisoning more easily. Oxide cathode positive ions strike capacity is poor, so that when the tube cathode operates in a continuous transmission state, applies only to the anode voltage is lower than the 3000V.
Author: Wang set
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