Vaccum Tube Amplifier
A vacuum tube is somewhat like a light bulb: constructed of glass and inside this glass envelope there is a heated filament. The interior of the tube has all the air evacuated (thus the vacuum). The heated filament gives off light, which we can see, just like a light bulb.
However, the light in the tube is just a byproduct and the light just looks good. Of more importance are the electrons which hover around the heated filament. Vacuum tubes contain other elements which are the real reason for their function. In a basic tube, there is the filament (often called the cathode), and a metal strip (called the anode or plate) situated near the inside edge of the tube.
When a positive voltage (usually in the hundreds of volts) is connected to the plate, the electrons at the cathode, by their negative charge, are attracted to the positive charge of the plate.
Flow of electrons from one point to another is called "current" (measured in amperes, or "amps"), and movement of electrons from the cathode to the anode falls into this category.
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