What Are the Different Types of Chromoly Tubing?

The color picture tube is in a vacuum state, and the electron beam excites the phosphor powder coated on the glass screen to emit light. The device converts electrical energy into light. The process is to use an electrical signal to control the electrons emitted by the cathode, and focus the electrons into electron beams that are deflected and emitted onto the phosphor, which converts the video signal into an optical signal. The electron beam of a color picture tube is restricted by the color selection mechanism. The electron beam is used to excite the phosphor strips corresponding to them, and the phosphors are excited to emit light to reproduce a color image.

A color picture tube is a traditional color display device. Its working principle is basically the same as that of a black and white picture tube. It is a cathode ray tube with electrostatic focusing and magnetic deflection. In recent years, some new color TV display devices have appeared, such as liquid crystal display devices and plasma display devices. Due to their small size and light weight, they have great advantages over traditional cathode ray tubes. In many image display fields and color The television display field has achieved rapid development. Nevertheless, the traditional color picture tube is still the mainstream of TV display devices because of its mature technology and simple display circuit. According to the principle of the three primary colors, three phosphors need to be coated on the phosphor screen of the color picture tube, and three electron guns need to be provided. Therefore, the color picture tube and the black and white picture tube have many differences in structure and working process. Structurally, there are generally three types of color picture tubes: a shadow mask type three-gun three-beam arm, a purlin type single-gun three-beam tube, and a self-converging color picture tube. Currently, a self-converging color picture tube is widely used. The phosphor screens of traditional picture tubes are mostly spherical screens. The ultra-flat and flat-flat color picture tubes that have appeared in recent years have the same working principle as self-converging tubes.

The characteristics of the three-gun three-beam shadow tube are: three independent electron guns, each of which has a separate filament, a cathode control grid and an accelerator, and a collector and anode high voltage are common.

The single-gun three-beam grid picture tube is characterized by a large electron beam diameter, high electron transmittance, and simple correction of moving picture convergence.

The characteristics of self-drawn poly picture tube are: self-drawn poly, strip phosphor and short neck.

In the large-screen color picture tube, it can be further divided into an ultra-flat picture tube, a flat-screen picture tube, an ultra-thin picture tube, and an ultra-clean picture tube. The main ones are three-shot three-beam color picture tubes and single-shot three-beam picture tubes.

The three primary color signals of R, G, and B are applied to the three cathodes of the color picture tube to control the beam currents of the three electron beams. The relationship between the control voltage between the grid and the cathode and the electron beam current is called the modulation characteristic of the picture tube.

Figure 4. Picture tube modulation characteristic curve

It is expected that the relationship between the beam current and the grid-to-cathode voltage is linear. But in fact, the beam current and the grid-to-negative voltage have a -th power relationship, 2.2 ~ 2.8. This causes distortion of the brightness of the image. For this reason, anti-distortion processing is required on the three primary color electric signals at the camera end, which is called gamma correction.

In fact, the three modulation characteristic curves of the picture tube do not overlap, and the cutoff voltage (the grid-to-negative voltage when the beam current of the electron beam is just zero) is also different. This will cause the following problem: when R = G = B, the color of the image should be standard white light, but from the modulation characteristics of the picture tube, it can be seen that when the three cathode potentials are equal, the currents of the three electron beams are not equal, so The red, green, and blue light emitted by red, green, and blue phosphors cannot mix out standard white light. Moreover, even if the modulation characteristics of the three electron beams overlap and the beam currents are equal, the standard white light cannot be reproduced because the three phosphors have different luminous efficiencies. This is called white imbalance. To this end, an amplifier that excites the three primary color signals of R, G, and B of a color picture tube is provided with an adjustment circuit. When R = G = B = black level, adjust the output voltage of the three amplifiers to make it equal to the cut-off voltage of the three cathodes of the picture tube. This is called dark balance adjustment in white balance. When R = G = B = white level, adjust the gain of the two amplifiers so that the color of the displayed picture is standard white light. This is called the bright balance adjustment in white balance. Therefore, there are generally five adjustment potentiometers for white balance adjustment, of which three are used for dark balance adjustment and two are used for light balance adjustment.