I'm trying to write some tube descriptions for a layman because I think they're useful and because describing them to others often helps me understand them better. So is the following simplified description of a cathode follower accurate? I think I'm getting it, but I'm not totally sure.
Edit: this isn't meant to be a recipe for a cathode follower or an application for a specific tube/circumstance, it's just meant to explain the most basic concepts of what happens when a cathode follower is doing its thing.
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[for a grounded cathode] We know that the grid will have a more negative voltage potential than the cathode because otherwise it starts attracting the cathode’s [emitted] electrons instead of allowing them to zip to the anode. When the grid is very negative, it doesn’t allow many electrons (current) through and when the grid is not quite so negative, it lets more electrons through (remember that same charges repel each other). The grid’s negative relation to the cathode is achieved by referencing it to 0V. [replace 0V with "ground or a voltage divider in the cathode"?]
Consider the numbers in this example. What’s the voltage dropped across a 10,000 ohm cathode resistor when the circuit draws 15mA?
V = I * R
.015 amps * 10,000 ohms = 150 volts
Now if a positive change in the grid (making it less negative) allows another 5mA through the tube, what is the new voltage drop across the cathode resistor?
(.005 amps + .015 amps) * 10,000 ohms = 200 volts
So the cathode voltage goes up, but as this happens, the grid’s voltage in relation to it is actually becoming more negative. This lets fewer electrons through to the anode. Fewer electrons means lower current and lower current actually means less voltage across the cathode resistor.
This all happens simultaneously, like a tug of war, and results in an increase in the current of the signal, but no increase in the voltage (it’s actually a slight decrease). It doesn’t amplify the voltage, but it does add power (because watts = voltage * current).
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Probably a description of impedance would follow this. Am I on the right track here? Please keep in mind that I'm trying to make this as conceptual (and non technical) as possible without being totally inaccurate.
Edit: this isn't meant to be a recipe for a cathode follower or an application for a specific tube/circumstance, it's just meant to explain the most basic concepts of what happens when a cathode follower is doing its thing.
"
[for a grounded cathode] We know that the grid will have a more negative voltage potential than the cathode because otherwise it starts attracting the cathode’s [emitted] electrons instead of allowing them to zip to the anode. When the grid is very negative, it doesn’t allow many electrons (current) through and when the grid is not quite so negative, it lets more electrons through (remember that same charges repel each other). The grid’s negative relation to the cathode is achieved by referencing it to 0V. [replace 0V with "ground or a voltage divider in the cathode"?]
Consider the numbers in this example. What’s the voltage dropped across a 10,000 ohm cathode resistor when the circuit draws 15mA?
V = I * R
.015 amps * 10,000 ohms = 150 volts
Now if a positive change in the grid (making it less negative) allows another 5mA through the tube, what is the new voltage drop across the cathode resistor?
(.005 amps + .015 amps) * 10,000 ohms = 200 volts
So the cathode voltage goes up, but as this happens, the grid’s voltage in relation to it is actually becoming more negative. This lets fewer electrons through to the anode. Fewer electrons means lower current and lower current actually means less voltage across the cathode resistor.
This all happens simultaneously, like a tug of war, and results in an increase in the current of the signal, but no increase in the voltage (it’s actually a slight decrease). It doesn’t amplify the voltage, but it does add power (because watts = voltage * current).
"
Probably a description of impedance would follow this. Am I on the right track here? Please keep in mind that I'm trying to make this as conceptual (and non technical) as possible without being totally inaccurate.
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