Tuned Transistor RF Amplifier
On the circuit below, the load resistor has been replace by a tuned circuit, C4 and L1. The tuned circuit is high impedance at resonance. The impedance is low at all other frequencies. Therefore, the signal which is amplified only at the resonance frequency.
Since this type of amplifier is normally used in RF application, the capacitors can be much smaller in value than those used at audio frequencies. We can see very popular application of this circuit in intermediate frequency amplifier stages that employ transistors in old radio receiver design.