Quote:
Originally Posted by orbsycli
so they just "amplify the signal" ?
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One of the first things that vacuum tubes performed was to amplify a weak signal that could be picked up with an antenna. The amplified signal then could be used to drive a speaker. Voila!! "dah-dit-dah-dit dah-dah-dit-dah"
Consider the incredibly professional looking drawing that I have attached.
This is a basic Triode, as it has 3 elements in the tube. The middle element is called the "grid" because it was often a piece of... well... call it "fly screen".
A large voltage is applied to the left pin, say 100 volts. This heated the "filament" or "anode" on the left side, so that it emitted herds of angry electrons (the blue arrows), that were attracted to the positive element on the right (the "cathode").
If no voltage at all was applied to the grid, then a steady voltage would come out the cathode. Most of the electrons flow freely and with much
esprit d'corps over to the right element.
We'll say half of them, 50 volts would be the normal, and the other half of the electrons are wasted on the glass tube (which makes it HOT).
But now, let's put a tiny, weak, sickly electrical signal to the grid. Say, a signal that only goes from -5 volts to +5 volts. All this does is give the grid an electrical charge; no current actually flows.
But the grid, with its tiny tiny plus or minus charge, makes a HUGE difference in the amount of current flowing from anode to cathode (blue arrows).
A tiny -5 volts potential can TOTALLY STOP all flow of current in the tube!
A tiny +5 volts can pull ALL the electrons from the cathode and deliver a whopping 100 volts to the cathode.
And so a tiny input signal at the grid can impose its identity on a HUGE flow of current from anode to cathode. The little signal at the grid has been DUPLICATED with a much larger amplitude--we call this "
amplification".
Re: Tubes
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