Valves structure operation and use

Posted on Feb 5, 2014

The first television set I ever saw appeared in our house in about 1950. It looked like this - except it was in a box, obviously. My dad had built it from a kit. They made their own entertainment in those days. There was only one channel - BBC - broadcasting on 45 MHz. The programmes were rubbish, the picture was a grainy black and white on a 9` t

Valves structure operation and use
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ube, and yet my brother and I were entranced. It was the most amazing thing we had ever seen. Moving pictures! Right there in our living room! Some pedants refer to valves as `thermionic` valves, to distinguish them from the valves plumbers fit, whilst Americans know them as `vacuum tubes`. They look like oddly shaped light bulbs, or fat metal tubes. There are six of them visible in the picture. (OK, Don, seven if you count the CRT). Think of a plumber`s water valve, or a tap. It`s basically a pipe with an adjustable vane inside it. The vane can be rotated from outside the pipe between fully closed and fully open. You can control precisely how much water flows through the valve by adjusting the angle of the vane. A valve like those in the TV set works by controlling the flow of electric current. The key point is that both types of valve allow an external force to influence what`s happening inside. These valves control electric current. A current is a stream of electrons, all flowing in the same direction. So a valve needs a source of electrons, a target for them to aim at, and a force to move them. Plus, of course, a means of controlling how many electrons are moving. Engineers needed a way of thinking about a valve without worrying about unnecessary details such as its physical size or the actual shape of its components. They came up with a descriptive symbol. I found this version in the March 1923 edition of Modern...

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