A small MOS FET is often used for PA of QRP rigs. Here is the specification of the FET. The maximum Power is 400mW but QRP rigs are used for 1W power output PA. The schemantic of DC40A has 2N7000 for PA and there is no loading resistor. Once the gate of 2N7000 gets the RF voltage, the FET acts as a high-speed switching element. Therefore, the element generates a large power at the switching cycle.
The schemantic shows that the output of Q3 2n3904 is 8V p-p and its of Q2 2N7000 is 45 p-p.
The artcile of MOS FET amplifier is usefule to understand MOS FET. You should understand the properties of FET and how to use FET for the amplifier.