Goodbye CRT

by Bob Seidel

I did some shopping this week at the local electronics stores in Wilmington, and realized that the death knell has been sounded for the traditional CRT (Cathode Ray Tube) computer display (or monitor). CRTs are one of the last holdouts of vacuum tube technology. All electronics gear used to be composed of tubes, but most young people these days have never even heard of a tube, nor even seen one except the face of their televisions.

An American, Lee de Forest, based on some earlier work by Edison, invented the vacuum tube in 1906. In the tube, a heated element (called the cathode) would emit a stream of electrons, which were accelerated towards another element (called the anode or plate). A third element between them could be used to control (or modulate) the stream of electrons. A tube thus was able to amplify and control an electronic signal. The control or acceleration was done by applying various voltages to the tube elements. Tubes generally had fairly hefty 6 or 12 volt power supplies for the cathode heater to generate the electrons, and often 250 volts or more applied to the plate. This required some fairly large and expensive power supplies, and the tubes themselves were very hot. Tubes powered all radio and electronic equipment until the invention of the transistor.

The CRT is just a variation of a vacuum tube in which the accelerated electrons strike a plate having phosphors that glow when the electrons hit (or excite) them. What we see when we look at a television or a computer display is these phosphors.

Home televisions became popular in the late '40s and early '50s and had perhaps 20 or more tubes in them. Servicemen carried large boxes of standard tube parts and would generally fix a television by swapping tubes with known good ones until them found the source of the problem. One or two tube failures a year were common. Local electronics stores had tube testers (and sold tubes), and it was common to see do-it-yourselfers queued up on a Saturday morning to test their tubes.

CRTs were actually used in early computers not as displays but as storage devices, as magnetic core memory technology had not yet been perfected.

The invention of the transistor sounded end of the vacuum tube except for specialized applications. Transistor circuits were smaller, required less voltage, were cooler, and generally much more reliable. Vacuum tubes were still used for very high power radio amplifiers and the CRTs of televisions and computer displays.

Alternate technologies to the CRT began to emerge in the late '70s, with the invention of the plasma display. I worked on plasma displays at IBM at this time. The plasma displays were crude by today's standards, and only had one color - orange - the color of excited neon gas. But these displays were very expensive and the lack of full color was a detriment to sales. IBM actually had a plasma (or gas panel) display marketed in the early '80s.

The late '90s brought the LCD and the full color plasma display. These displays are much thinner and lighter than equivalent CRTs but cost more to manufacture.

In the '80s and early '90s, good CRT displays for a PC cost from $400 to $1,000 or more. I remember buying an excellent Sony 17" display for $850 and agonizing over the decision. With the advent of the LCD, CRT prices began to plummet to the point where you could recently buy a 17" unit for less than $100.

But now the CRTs are all but gone. There were only a few ones left on the shelves last week and those were not going to be replaced once gone. Why? First and foremost is the profit margin - these stores make a lot more money on a $400-$500 LCD than a $100 CRT. The CRT is much bulkier to store in the warehouse and is more fragile. LCDs have become popular in homes and offices because they are much flatter (more desk room) and do not generate any heat.

So, the CRT display for a PC is now a dinosaur, and for televisions it is just around the corner. Many people believe that CRT televisions still give you a superior picture, but I had to admit that the plasma TVs I saw (and almost bought) on this same shopping trip were gorgeous. I know there will be a plasma TV in my living room in the near future!

(Bob Seidel is a local computer consultant in the Southport / Oak Island area. You can visit his website at www.bobseidel.com or e-mail him at bsc@bobseidel.com).