The preamp creates voltage, but voltage alone cannot move a heavy speaker cone. You need current . The power amplifier converts the line-level signal into a high-power replica of the input signal.
: Block DC voltage while allowing AC signals (the music) to pass through. They are critical for "coupling" different stages of the amp.
: Learning how different electronic components introduce overtones that define a "signature" guitar tone. Would the focus for the next part of this overview be on vacuum tube specific physics or solid-state semiconductor theory? Guitar Amplifier Electronics: Basic Theory - Amp Books