Here is a very simple BC549C transistor amplifier circuit using an LT700 Transformer to drive a loudspeaker.
If you are using The Little Whippersnapper's Crystal Radio system and need a simple circuit to drive the loudspeaker, then this will work. Enjoy!
Biased Transistor Circuit
Here is a perfectly biased transistor amplifier circuit for use in an electronics project. It is biased for precise mid-point operation at 4.5 V, when the power to the circuit is at 9 V. This makes an ideal second stage or third stage amplifier circuit to amplify audio signals.