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Maybe the CRT Isn't Quite Dead Yet

You may be hearing about the demise of the venerable CRT, which has been the display device used in most of the TV sets we have watched since television became a commercial reality. Big, heavy glass CRTs are disappearing from the shelves of neighborhood consumer electronics stores in favor of the smaller, lighter, and most importantly thinner LCDs, plasma panels and microdisplay projector sets. This phenomenon is well underway in places like the United States, Europe and Japan.

One recent report has it that one of the Korean leaders in flat-panel display development and manufacturing has limited CRT sales in Europe to stock on hand, ultimately aiming to stop selling CRTs there altogether.

But wait! This is not the entire story. Korean display manufacturers, which account for much of today's display innovation, have found a new lease on life for CRTs in some parts of the world. They have done this by developing and selling so called "slim CRTs," which have significantly shallower depths than do conventional CRTs.

One 32-inch slim CRT, for example has a depth of about 350 millimeters or about 13.8 inches, as compared to a conventional 32-inch tube's depth of 500 millimeters, or 19.8 inches. This is a reduction of six inches, or about 30 percent, and it puts it into a size category that is competitive with a microdisplay rear-projection set of similar screen size, at a significantly lower price.

So CRTs aren't quite dead yet, and in fact, some new technological innovations are occurring in the CRT display field.

The reduction in CRT depth requires a commensurate increase in deflection angle, which in turn requires higher deflection currents to swing the electron beam over the wider angle.

Higher currents cause greater heat buildup in deflection coils and their driving electronics. Traditional CRT deflection amplifiers are analog class AB amplifiers, but another innovation is the use of Class D amplification, which employs pulse width modulation rather than traditional analog amplification.


Class D amplification significantly increases efficiency and reduces heat buildup in the amplifier circuitry.

The forces at work in the marketplace have caused several things to happen. In the United States, Europe, Japan, and other places, the profit margins on traditional CRT TV sets have become so low that marketing is totally about price--there is no substantive premium market for them anymore.

However, in areas that have many first-time TV set buyers, such as China and India, there have been recent significant increases in the sales of low-end CRT sets. Smaller-screen slim CRTs can find a place in those markets at higher margins than traditional sets. Slim CRT sets were recently introduced into the Middle East as well.

It is not a complete surprise to learn that many of the plants that make slim CRTs are located in Eastern Europe; the former Soviet republics are home to many of today's vacuum tube manufacturing facilities--just ask any tube amplifier high-fidelity aficionado.

The market for slim CRTs has been enhanced on the lower end by the recent addition of the 21-inch category to the 32- and 29-inch size categories. The thinner depth has permitted a price premium of about 30 percent on slim CRT sets over those with standard CRTs, which still makes them cheaper than flat-panel sets. On the down side, it must be said that recent further drops in flat-panel display prices have slightly eroded slim CRT sales.

There are some significant disadvantages to CRT displays with which we are well familiar. Traditional CRT sets have had significant depth dimensions, and the weight of a cathode ray tube increases geometrically with its screen dimension, as more and thicker glass is required. There is little technology on the horizon that might help to break the current CRT screen size barrier, which is about 36 inches, as a CRT set of this size weighs several hundred pounds.

However, as we see, there is technology that makes a slim CRT set in the 32-inch range competitive in depth (but not in weight) with a flat-panel display, at a lower price. A CRT display has a less even output than a fixed-pixel display, with a light output falloff occurring as the edges of the screen are approached.

And there is no argument that microdisplay projectors are considerably better performers than CRT projectors. But within the range of direct-view screen sizes, CRTs are capable of making very good pictures.

Slim CRTs are a very good fit in the developing television marketplaces, in that although they are more expensive than traditional CRT sets, they are available at attractively low prices, and their size parameters work well with smaller living quarters.

It is not likely that slim CRT sales will soar in the United States or Europe. But in many developing television markets, they should do well.