Biasing Transistor Amplifiers

I thought it'd be fun to do some theory on my method of biasing a class A BJT transistor amplifier. I also show classes A, AB, C & D. Most of the time is spent on class A, but it gives you an idea on how to calculate a reasonable quiescent point with a predetermined load. All circuits are bread-boarded with the exception of a 2.5W class D amplifier which I demonstrate with an Adafruit PWM breakout board.