 A CRT is a Valve
Basicly a CRT.... or Cathode Ray Tube is a large old fashion Thermionic Valve.... the basic idea is over 100 years old.
Put in simple terms, It consists of a Heater and Negative Cathode....... (these days i think they are combined into one as the old fashioned seperate heater filiments had a tendancy to blow, like an electric light.)
The heat causes electrons to get excited and escape the negative charged Cathode and be attracted to, and travel in a vacum towards the Positively charged Anode.....
The electrons are manipulated and controled on their way towards the Anode by control grids... and deflection coils that cause the electron beam to travel from side to side and up and down on your screen..... (Like a Wobbulater)
They also pass through a focus control grid.
Phospher dots on the inside of the front of the tube light up as they are hit with the beam of electrons...... hence this beam of electrons literaly paints a picture on the screen for you.....
With Colour CRT's there are three sets of Cathodes and Control grids, (or three guns,) firing at the screen.... This produces the primary colours of Red Green and Blue..... in turn these are focused onto Red, Green and Blue, Phospher dots on the screen...
All your colours except black are then displayed on the screen from these guns.......
The colour black is produced when the guns arent firing and you just see the shadow mask which is a plate which has a multitude of holes in it, through which the beams pass just before they hit the phospher dots...
White is produced by all the colours being present at once and the pureness of the white is a very good indicator of how good a TV picture is!
Its still one of the best means of producing a TV picture.....
But there are some very interesting advancements in the pipe line besides Plasma, LCD, and Projection, that will I feel will come to the for over the next two or three years.
Regards John (Retired Service Engineer)
Last edited by JPC; 03-12-2002 at 11:22 PM.
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What does CRT mean 
Linear Mode
