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CRT TV - Yesterday’s news or unsung hero?




Cathode Ray Tube televisions seem to be a thing of the past. They are not very fancy, relatively heavy and often bulky. While theoretically available in widescreen 16:9 you will have a hard time actually finding one with a screen size larger than 36”. And even the 36” seem to be at the brink of extinction these days. Manufacturers almost completely pulled out of the market for tube-based sets greater than portable.




At first glance this is no surprise. The technology behind CRT is over a century old. It goes as far back as 1897 when Ferdinand Braun invented the Braun tube. The idee is even older and was first layed out in a patent by Paul Nipkov in 1886. That's ancient! Also; the screen size is limited and the devices are massive. Flat screens at the sames time are becoming bigger, slimmer and cheaper every year. They look fancy, they have cool names, they are light, cheap enough and state of the art. Surely CRT televisions must be a thing of the past. But are they?


Manufacturers are still reluctant to give up the technology. CRT certainly will no longer grow but giving it up all together would be foolish. At second glance CRT still offers a few undeniable advantages over its rivals. Should you already own a modern flat screen you can probably guess one of them: The picture quality.

Even a state of the art Plasma is no match for a good old fashioned CRT when it comes to the sheer quality of the picture!

Let’s have a look at them then.




Technology

CRT stands for "Cathode Ray Tube". It works in a very simple way; kind of anyways. What happens is; an electronic ray is generated in a vacuum tube, then accelerated, deflected and it eventually hits a coated screen that starts glowing where the beam hits it. Very simple really; except that it isn’t. It is actually quite ingenious.

The electronic ray is generated in a part that is called cathode (hence the name). It is the negative counterpart of a anode where the two describe terminals in electronic systems. All you need to know about it is that electrons carry a negative charge and opposites attract.


When the cathode is heated up it naturally emits electrons. These electrons (or better their negative charge) are attracted by the anode so they travel towards that direction in the vacuum tube.

The anodes main job is to focus the stream of electrons into a beam. All that is needed then is a way to control this beam. Sounds simple?

In CRTs the beam is generally controlled by magnetic fields. In the original design this was actually achieved by a mirror like reflector, magnets allow a more compact design though.

The beam is now directed to a screen. This screen is covered by a phosphorus material which starts glowing when hit by the beam. This creates a dot of light which you can see on the other side of the screen.

Cathode Ray Tube - principle

Copyright note: This diagram was taken from Wikipedia and licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Vector: Interiot Raster:Theresa Knott



To create a picture quite a few dots need to be lit up and ideally at the same time. Since there is only one beam (three with colour screens) this means this whole thing has to work fast.

Indeed it has to work extremely fast since one picture is nothing to the human eye. Depending on the refresh rate it would create 50 up to 100 pictures a second to fool your eyes into believing that the picture moves. One can't even begin to imagine at what speed all this is happening. It really is astonishing. To think that this amazing technology has been around for a good 75 years now is staggering. We are talking about pre World War II!





Drawbacks

The biggest drawback of a CRT is certainly the fact that it is rather bulky. It is also rather heavy.

After what you just learned about the design of these televisions it is quite obvious that there is no real solution for the factor weight. A vacuum tube that is under considerable pressure (approximately 1 kilogram per square centimeter) so it has to be build to withstand it. The screen itself is made from solid glass as well. There is a limit to what you can achieve in reducing weight and a CRT will never be a match for LCDs.

A modern wide screen CRT is surprisingly slim. They may not be as slim as Plasmas and LCDs but quite frankly when put on a rack it makes no real difference. You can’t hang it on to a wall but honestly; who does that anyways? Samsung for example with their SlimFit series managed to build a 30” widescreen that is only 16.3” deep. That’s not bad.

What many people see as a drawback is also the fact that the screens are not entirely flat. I would put it this way: most modern sets aren’t exactly curved. At the high end they are completely flat. And even if they are a little bit curved; in reality it makes little to no difference.

It originally was a selling point for the Sony televisions that where almost perfectly flat in a time when most teles still looked like a balloon. The idea behind is that on a curved screen you have distortions and more glare than on a flat. While this was certainly true 20 years ago I wouldn’t even consider this a drawback anymore.

What is true is that a CRT has a half-lifetime of "only" 20.000 hours. After that the brightness of the image will have fallen to half its original value. That is design flaw that is literally impossible to fix. Putting it in simple terms is: The phosphorus material weakens itself by the "glowing". Just like nuclear material it has a half life. While initially very bright and strong and gets weaker with any use. That it loses half its original brightness doesn’t mean though you have to throw it away. It will still be fine.




Advantages

The main reason why CRT’s on a global scale still have a market share of around 70% is the price. They are half the price of a LCD and sometimes even less. They are robust, work under most conditions and they are easy to set up as in they work out of the box. All these reasons make them a popular choice for nurseries, garden sheds and caravans. But that is only one side of the medallion.

Purists will pick a CRT over plasma TV or LCD TV for one reason. The quality of the picture is unrivalled by any of the other systems. Or let me put it this way:

If you go for a modern and state of the art high end CRT you will get a better picture for less money and with almost no drawbacks!


The only limit you have to accept is the size of the screen. There simply aren’t any televisions greater than 36” available anymore. For all I care this is the only real drawback to Cathode Ray Tube televisions.


 

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