Deflection Yoke

Deflection Yoke - pictured below, wraps around the neck on the CRT and extends partway up along the sloped sides.  The yoke has signals running through it's wires that create a strong electrical/magnetic field - rapidly deflecting the electron beam, scanning across the screen to paint full frames at a rate of 60 frames per second.  The entire concept is truly amazing.

  

Working Principle of CRT

      The electrons emitted from the cathode makes an electron cloud. This electron cloud then forms the electron beam. This electron beam then with the help of the yoke or the combined horizontal and vertical scanning coil moves left-right and up-down. By this process the beam hit the screen of the CRT. As the CRT has many dots which are light sensitive and coated with the phosphors. The phosphor chemicals are light metals as Zinc (Zn) and Cadmium (Cd) in the form of Sulphide, Sulphate and Phosphate compounds.

Construction Details of CRT

1)  Electron gun:

It is very simple device which mainly produces thin electron beam. It is the combination of Heater, Cathode and the Grids. All this components are situated at the base of the tube. The heater heats the cathode and then the cathode emits a lot of electrons which make an electron cloud. The electron gun is analogous to the pen. In different parts of the electron gun different types of voltages are required. These voltages vary within the range 200-600 Volts. The electron gun receives voltages from the receiver which is connected with the base pins of the CRT.

2) Heater:

The heater is mainly used to heat the cathode. It is made of metals and twisted in shape. It heats the cathode indirectly. It needs 6-24 Volts dc or ac supply voltage.

Scanning Coils of Television

Actually the main duty of the video section is to scan the picture on the screen so that the viewers can watch them. For this only purpose the vast arrangement is needed. The scanning coil is the most important component for the video section. It is located on the base of the CRT. The electron beam produced by the electron gun is finally directed by the scanning coil with different frequencies. The scanning coil is nothing but just a device to produce magnetic field. This magnetic field deflects the electron beam to and fro. We know that the scanning process is analogous to writing on the paper with a pen. That is, it needs to go first towards horizontally and then vertically. For these purposes there need two different coils. One is horizontal scanning coil and another is vertical scanning coil. These two coils are named as ‘Yoke’ together. This yoke is fixed outside the tube and close to the neck of the tube just before it begins to flare out. For two different types scanning there need two different types of scanning coil. One is the horizontal and another is the vertical scanning coil.