The Theory of Nothing

How did the vacuum tube change the world?

How did the vacuum tube change the world?

Most of you have probably never heard or seen a vacuum tube. They were once employed in radios and TV’s back in the dark ages. Just kidding! Actually, vacuum tubes were replaced by transistors and nowadays by integrated circuits. This replacement effort began to gain momentum in the 60’s and these ancient devices are seldom used now. They can be seen in museums.

However, the vacuum tube or valve as it’s called in Britain made modern electronic devices possible, including the digital computer. The vacuum tube came about because of experiments by people like Edison with evacuated light bulbs. He found that electrons emitted by a filament could be attracted to a positive plate. John Ambrose Fleming, an English physicist, is credited with inventing the electron valve or vacuum tube in 1904. It was just a simple diode, meaning it could only pass current in one direction, but it represented a big improvement as an alternating current rectifier and as a radio detector.

The addition of a third element made amplification possible. This invention was called a triode. The way that a vacuum tube works is that a filament heats an emitter--a structure that emits electrons when heated called a cathode--and the resultant electrons are attracted to a positively charged plate, establishing an electron flow through a vacuum. All that needed to create amplification is a grid between the cathode and the plate. By placing an alternating signal on the grid, one can control a strong electron flow through the tube thus amplifying the signal. That’s why the Brits called it a valve. The grid acts like a valve in a water pipe to control a strong water stream. This idea is important to the development of modern electronic devices, including radio, TV, stereos, sound systems and even radar and computers. Their use in computers was very inefficient and failed too often. The invention of solid-state devices like transistors and integrated circuits made modern computers possible.

Vacuum tubes went through many improvements in the first half of the 20th century. They were made smaller and more efficient and easier to manufacture. One kind of tube made TV’s possible. The Cathode ray tube was a device that was used in Oscilloscopes to observe electronic signals. This idea was adapted to create a TV picture tube, something that has been replaced only recently in computer monitors and TV’s.

A cathode heated by a filament produces electrons that can be attracted by positively charged plates to strike against a curved glass screen that is coated with a phosphorous type material that glows when struck by electrons in a vacuum. By use of magnets and special grids, the electron beam from the cathode can be focused and moved around to cover all areas of the screen. This idea allowed a signal to sweep the beam across and down the screen to produce an image by doing it fast enough to fool the eye into thinking it’s instantaneous because of the persistence of vision, a property of our eyes that makes an image stay for a split second before vanishing. Eventually, using three cathodes that were aimed at red, green and yellow dots patterns on the screen’s phosphorescent coating made a color cathode ray tube possible. Needless to say that none of this applies to the digital methods that make LED flat screen HDTV’s work today. Cathode ray tubes required high voltages in order to cause electron beams from cathodes to impact the tube’s phosphorescent coatings with sufficient energy to work (emit light). All of these actions consumed a lot of electricity.

Oh well, at least you’ll know something about these antiquated electronic devices if you see them in a museum.

Thanks for reading.