I thought the:
- clean current would get into the transistor through the collector
- the signal inserted through the base
- the current from the collector would combine itself with the signal
- that would emit from the emitter an amplified signal
but by looking at most circuits that amplify with one transistor they all place the output before the collector. Why?
Because that's not how transistors, or FETs, or vacuum tubes (valves) work!
Imagine, if you will, the transistor in your Schematic being replaced by a variable resistor with a knob you can turn to increase or decrease the resistance.
This device, which we can call VR1, along with Rc, forms a voltage divider between your "power source" & ground.
The "output signal" is the voltage between the junction of Rc & VR1, with respect to ground.
If you move the knob controlling VR1 fast enough, you get a varying voltage at the output which looks like a very low frequency audio signal .
,'
Imagine if you had superpowers, you could listen to some music & twiddle the knob in time with it.
If you listened to the signal with an amplifier & speaker, you would hear music!
Unfortunately, nobody has super powers, but early experimenters looked for ways to vary the resistance of part of a voltage divider to do something along those lines.
The first success was the carbon microphone.
The sound of someone speaking into the microphone varied the resistance of the resistive element, & hence, varied the voltage available at the output of the voltage divider made up of that element & its load resistor--- in many cases, the earphone of a telephone somewhere remote from the mic.
This gave them a very sensitive microphone, but it still didn't solve the problem of amplifying a signal which was already an electrical one.
One idea was to use a very sensitive earphone, mechanically coupled to a carbon mic.
This worked, but not too well.
Ultimately, the first workable vacuum tubes were made, revolutionising the field of Electronics.
The "tube" was still a "variable resistor", but one where the input signal controlled the amount of current flow through it, & hence, its effective resistance value in the "voltage divider".
Most amplifying devices, although the mechanism varies significantly, still are "part of a voltage divider".
Some circuit configurations are a bit hard to visualise as a simple "voltage divider", but it works well with the "Common Emitter" & " Common Collector"(Emitter follower) circuits, & their equivalents with other devices.
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