"Over the years I came to the realization that the biggest misconception is that an amplifier actually makes the electrical signal "bigger." Once I explained that this is not possible per se, they could then follow the metaphor of a water valve. One that concept was grasped, they would have an "aha moment" regarding the importance of the power supply."
Okay, I know that's confusing so let's step back a moment. Imagine our amplifier valve as that of a water faucet. The power supply is the reservoir of water. We know from that image the faucet cannot make more water than what is available from the reservoir. In fact, the valve can only let what's in the reservoir out or stop it from flowing. It cannot make more. So yes, an amplifier takes a small signal and makes it bigger - but not bigger than what's available in the power supply. The valve can only make something smaller than the power supply is capable of providing. It is, after all, a valve.
So now let's move to the example of an amplifier powering a loudspeaker. We all know that amplifiers have power ratings: anywhere from 1 watt to 1000 watts. What is the gating item that determines the output power of an amplifier? Is it the valve or the power supply? If you guessed power supply, congratulations, you win the prize. Ignoring some of the practical limitations we engineers face when designing equipment for a moment, the difference between a 100 watt power amplifier and a 500 watt power amplifier is not the valve (amplifier) but the power supply. Take a 100 watt amplifier, replace its power supply with one 5 times more powerful and you have a 500 watt amplifier. Plain and simple.
Yes, yes, let us not pollute our understanding of these basic ideas with details such as: bigger heatsinks, stronger valves, etc. I am not trying to help you design a new amplifier.
Amplifiers can only make what their power supplies offer smaller, never bigger.
So why do we call them 'amplifiers' when, in fact, they are only valves? For the same reason a small turn of the faucet can release a huge and powerful stream of water. It amplifies the small force into the bigger force but - and here's the key - never bigger than the power supply.
And never better than the power supply. Let that be your food for thought and our starting point for tomorrow's discussion.