Power amplifier

Power amplifiers may be for different purposes. For radio transmitters and usually audio systems. There are both stereo and mono power amplifiers, the latter also called mono block power amps. They may have stronger effects, one to several hundred watts.
Some are intended for PA systems, hence called PA amplifiers.

The most popular power amplifier type is probably the tube power amplifier, either in mono or stereo. Some only use tubes in the final amplifier stage and some use tubes all the way. Nearly all high power tube amplifiers use the Push-pull (PP) type. In push-pull amplifiers, the cancellation of the differential output tubes that occurs, largely cancels the dominant even order harmonic distortion of the output stage, which results in a reduced THD, albeit dominated by odd order harmonics. Therefore, the "musical" overdrive distortion known as the "tube sound" that refers to class A tube amplifiers, is not present. High power class A tube amplifiers may be very expensive due to even larger or more tubes, and run very warm due to the lower power efficiency.