If the amplifier class B need two transistors to work properly, then there are the so-called class C amplifier that only need 1 transistor. There are few applications that really only requires a positive phase only. An example is the pilot frequency detector and amplifier, RF tuner amplifier circuit and so forth.
Class C transistor amplifier active work only on the positive phase only, even if the need is quite narrow only the peaks are strengthened. Time signal can replica by series resonance of L and C. Typical of the series class C amplifier is like in the following series.
|Basic Schematic Power Amplifier Class C|