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| Amplifiers, Audio Distribution & Audio Frequency, Af Amplifiers
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The audio distribution & audio frequency (af) amplifier helps in supplying af (audio frequency) power to operate the loud speaker, handpiece or other output device. They are largely used in audio devices and supply af (audio distribution & audio frequency) power of various frequency ranges. These af (audio distribution & audio frequency) amplifiers have three stages using one vt-triode and three vt-pentodes. The af amplifier stage includes a volume control and sometimes treble and bass controls and with a squelch or muting facility. The grid of the first tube is connected to the moving arm of the audio gain control through a blocking capacitor. The plate of these amplifiers is coupled to the grid of the second amplifier by means of a capacitor, plate resistor and grid leak. The second amplifier tube, while a pentode, is operated as a triode by connecting its plate and screen together. They are available in wide frequency ranges requiring diverse applications. They are used in different devices in different frequency ranges like low frequency for devices requiring low audio power level. In portable receivers the high frequency amplifiers are used.
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