In this electronic age, one of the most commonly used devices is the amplifier.
It has made possible magnification of minute indications of voltage, current and power into levels high enough to perform many useful tasks.
It is the purpose of this manual to present a series of amplifiers designed to cover the audio frequencies, frequencies that affect the human ear, and those that cover the entire range of sound.
The average listener is most sensitive to sound from about 100 cycles, a low pitch, to 7000 cycles (a high pitch).
In some instances, one can hear sound frequencies as low as 20 cycles and perhaps as high as 20,000 cycles.
An audio frequency (A.F.) amplifier, then, operates within this band of frequencies, either entirely or in part, depending upon the purpose for which it was designed.
The majority of (A.F.) amplifiers described in this manual are for purposes of amplifying the usual range of recorded sound, broadcast and voice frequencies, or from 50 to 12,000 cycles.
There are some instances of amplifiers described to operate up to 20,000 cycles, and these are designated as High Fidelity amplifiers.
All amplifiers shown are of standard design and typical of their type.
No attempt has been made to specify any but standard parts in the diagrams.