How do tubes work? How is a preamp tube different from a power tube? And what components/elements of preamp/power tubes affect the tone of the amp? (example: what makes EL34’s sound different than 6L6’s, or makes 12ax7’s sound different than ef86’s)
In: Technology
This turned out to be more like an eli15, sorry. I hope this is understandable.
TLDR: electrons go brrrr in vacuum grid says no.
**First, how do vacuum tubes work?**
If you take a piece of metal and heat it up until its glowing, electrons will start escaping and flying away atvarious speeds (this is called glow emmission). In a pure vacuum these electrons can fly freely, and you can use a second piece of metal to catch them again. This is what happens in a vacuum tube, there is a heated electrode (piece of metal) at the bottom, and a second (not heated) electrode at the top. When there is a voltage between these electrodes the emmitted electrons fly from the bottom to the top electrode: There is current flowing through the tube.
Now we take a third electrode in form of a metal mesh and put it between the other two electrodes. This is called the control grid. We now apply a second voltage from the control grid to the bottom (heated) electrode, so that it hinders the flow of electrons. You can think of it as rolling marbles up a ramp. The faster the marbles the higher up the ramp they get, and only marbles of a certain minimum speed will reach the top and fall off. And because the electrons emitted from the bottom glowing electrode all have different speeds only some electrons get past the control grid. The amount is dependant on the voltage we apply to the control grid.
**How do we use this to amplify signals?**
The signal from an electric guitar is very weak (only in the range of millivolts), but if we apply this small voltage to the control grid of a vacuum tube it results in a large change in the number of electrons that reach the top and therefore causes a large variation in current. If we force this current through a resistor it results in a voltage much larger than our input voltage. (Voltage is equal to current times resistance)
**Why do vacuum tubes sound different?**
The current that flows through the tube for each grid voltage depends on a lot of factors like the temperature of the bottom electrode, the shape of the tube, the size of the grid etc… This means the response for an input signal is different for each Vacuum tube and this makes them sound different.
I don’t really know how each component affects the sound individually, sorry.
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