Hobbies And Interests
Features
A vacuum tube has a glass casing. It is so called because the air inside of it is sucked out before the glass is sealed. Inside the casing are several parts, including a cathode, the negative side, which is made from a filament. The anode, or positive side, is a plate on which the electrical signal appears. A control grid, which is a piece of wire wrapped around posts, is also present. In most amps, the grid, located near the cathode, controls or modulates the electron flow. A vacuum tube is classified according to its number of grids. Those with two or more include a screen grid, which is located between the control grid and the plate, to isolate them from each other.
Screen Resistors
As the electrons inside of the vacuum tube flow from the cathode to the plate, some of them are attracted to the screen, giving it a current. This causes the screen to become very hot, so a resistor is placed in series with it to limit this current. Resistors have power ratings measured in watts, such as 1 watt or a 1/4 watt. If this rating is exceeded, they become damaged or destroyed. Vibration and damaged tubes can also damage screen resistors. Vacuum tubes are fragile not only because of their glass casing, but because they're high voltage. Like resistors, they have power ratings that must not be exceeded, or else they will become too hot.
Biasing and Resistor Failure
Biasing can produce screen resistor failure. Biasing occurs when DC voltage is applied to the same location where the AC signal is. For example, it can be a negative voltage applied to the tube's control grid. The voltage is usually set with a knob or trim pot resistor on the amp. A guitarist uses biasing to produce distorted sound from the instrument, which can be either an electric guitar or a bass. Since biasing increases the current, it can damage the tube, which can cause the screen resistors to fail. The increasing current can also damage the resistor directly.
Applications
Tube amps are used in a variety of applications. In addition to guitarists, other musicians such as organists, electric keyboardists and violinists use them. Hobbyists construct old-fashioned radios and other electric circuits with them. They're found in satellite transponders, which are electronic components in a satellite that are used for receiving and transmitting. Tube amps are still used for used radio transmitters, radio frequency amplifiers, stereos and radar.