Discussion in 'General TV Discussions Forum' started by british_cooper, Dec 3, 2002.
What does it stand for and is more advantagous than DLP and LCD?
CRT = Cathode Ray Tube
A rarer one these days is CRO (Cathode Ray Oscilliscope) and we all have monitors these days but up to the mid '80s they were VDUs (Visual Display Units)
Chris Muriel, Manchester
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)
He didn't actually ask how a CRT (ok "TV Tube") works but you gave a pretty thorough explanation.
Hope the original poster doesn't intend playing about inside the TV to measure the various voltages (like 25kV anode & high enough potential on the accelerator grids).
As a "Retired Service Engineer" , I guess you've hung up your wobbulator - always loved that word for a sweep generator
No more old ladies now telling you, when you ask what they think is wrong with their TV, that their "picture valve" has gone then.
Chris Muriel , Manchester - still have some PCL805s etc. around the shack somewhere
Not you as well!! I must have at least a dozen PCL805s in my shed!!
We could set in business together!!
Mind you even the larrge CRT's we have today are dwarfed by the huge Valves we used in our Short Wave Transmitters in Hong Kong in the 1950's......
Boy was it dramatic when you saw one of those melt down!
Kind Regards & 73's JOHN
Magic im glad you guys and guys clarified this , ive worked in AV
Industry 3 years and some one asked me the question and i couldnt believe i didnt know
Looking through "Collectables" on Ebay at http://listings.ebay.co.uk/pool1/plistings/list/all/category931/index.html?from=R4
I was astonished to see how collectable VALVES are these days especialy our old freinds....... PCL805s, ,
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