You can make a decent power amplifier using just three transistors. Also you just need a 9V battery to power this circuit. The circuit is ideal for a pocket radio or other hand held audio equipment.
The first part of the circuit here is a pre-amplifier consisting of transistor Q1(2N2222). The collector of the Q3 is coupled to the base of Q2 (2N2905A), which forms a complementary symmetry pair with Q3 (2N3053). The amplified signal is available at the junction of emitter of two transistors. Check out audio amplifier circuit too.
Q1 = 2N3053, Q2 = 2N2905A, Q3 = 2N2222
C1 = 470 microfarad, C2 = 1000 microfarad
R1, R2 = 3.3 ohm, R3 = 330 ohm, R4 = 20 ohm, R5 = 1.5K, R6 = 5.6K
K1 = 8 ohm’s Speaker
For Q1 you can try with any general purpose NPN transistors like BC107, BC148 etc. For Q2 and Q3 you can try any complimentary power transistors. The result may vary slightly, No problem.