How CRT Televisions Work

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A CRT TV set operates like a cathode ray oscilloscope with two time bases – one horizontal and one vertical. A beam of electrons produced at the back of the TV moves repeatedly across the screen. In the UK the horizontal time base is 0.000064 s and the vertical time base is 0.04 seconds. The net effect is that the beam moves across the screen 625 times in moving from top to bottom to generate 25 frames per second.

One electron gun is needed for each of the three primary colours – red green and blue. By varying the intensity of each beam according to the signal received by an aerial, both the brightness and the colour of each part of the screen can be controlled. A picture is then built up of many light and dark spots of different colours, much as in a newspaper picture.

CRT televisions are now superceded by LCD and LED screens, which are much lighter and reliable, consume less power and can be hung on the wall, so saving space.