#1
I'm doing a project about guitar and amplifiers, and I have read everything I could find on wikipedia about vacuum-tubes, but I don't really get it because there are so many hard words and stuff. So can anyone tell me if I'm right here:

The electric signals produced by the pickups of the guitar goes through the cable to the amplifier. In the amplifier, an electrode leads the electricity into the vacuum tubes. Here, the electric pulse also resonates in the tubes, and since I assume the electrode (or triode/diode) is electromagnetic, the waves in the tube is picked up by the coil in the electrode.

Also, wikipedia says an electrode is: "An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron (meaning amber, from which the word electricity is derived) and hodos, a way." In an amplifier, would a nonmetallic part of the circuit be the tube?

Thanks alot for helping me out. I need to hand it in tomorrow!
#2
Kind-of-sort-of-in-a-way-but-not-really

In order to understand tubes you need to know what a "cathode" and an "anode" are, be able to explain their respective roles in the amplification process, and understand their relationship to each other. You also need to research the differences between the diode, triode, tetrode, and pentode type tubes (start with the diode).

If you're having trouble with words, find a dictionary. I can't sympathize with anyone who fails to understand something because of the words are too hard.

EDIT: Also you will need to be able to explain the differences between common tube amplifier types (class A, class A/B).
ESP LTD EC-256 and a Fender Deluxe VM
#3
The thing is that this is a physics-project and you could choose any subject you wanted. Some chose airplanes, some chose astronomy (black holes and stuff), and I happened to choose guitar. I'm only 15 and in last year of elementary school so we have only made simple schemes in electronics (like battery, transistor, diode etc.) So very basic. This means that I don't need to explain it in detail, I just want to be able to understand it in easy words. If didn't want to, I could just skip this part (amplifiers). But I want to show my understanding in basic electronics and physics so just a simple explanation would be good.
#5
If you already talked about transistors, you should be able to explain how an operational amplifier (op-amp) works.

I don't think you will learn the complicated physics of a tube guitar amp on the internet and understand it proficiently. and then be able to teach others.
#6
Quote by ZanasCross
Wiki or dictionary cathode and anode, figure out how they work. Also, look up induction. The combination of all that should help.

Also; very basic and not exactly what you are going for but: http://entertainment.howstuffworks.com/electric-guitar2.htm

I understand that a cathode and an anode are the different sides of a diode.

"In a vacuum tube or electronic vacuum system, the cathode emits free electrons. Electrons are extracted from metal electrodes either by heating the electrode, causing thermionic emission, or by applying a strong electric field and causing field emission." "The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air. When hot, the filament releases electrons into the vacuum: a process called thermionic emission. The resulting negatively charged cloud of electrons is called a space charge. These electrons will be drawn to a metal plate inside the envelope, if the plate (also called the anode) is positively charged relative to the filament (or cathode). The result is a flow of electrons from filament to plate. This cannot work in the reverse direction because the plate is not heated and does not emit electrons."

Shouldn't this mean that the electrodes are released in the cathode, out in the tube, and then return to the positively charged anode? Why does the charge in easy words amplify?
#7
If I am remembering correctly (its been a few years since I seriously looked into this), the electrons are released by getting the cathode hot. The electrical signal will heat it in waves proportional to the amount of electricity coming from the guitar via induction. As the plate heats and cools, it will emit certain amounts of electrons. The electrons are then "pulled" very very quickly across the tube by the difference in charge, which causes even greater induction due to a magnet near the tube. This causes a much bigger signal; thus it is amplified.

That's going from a very rusty memory and some details could be quite wrong. I was about 14 when I looked that up (7 years ago).
#8
Quote by ZanasCross
If I am remembering correctly (its been a few years since I seriously looked into this), the electrons are released by getting the cathode hot. The electrical signal will heat it in waves proportional to the amount of electricity coming from the guitar via induction. As the plate heats and cools, it will emit certain amounts of electrons. The electrons are then "pulled" very very quickly across the tube by the difference in charge, which causes even greater induction due to a magnet near the tube. This causes a much bigger signal; thus it is amplified.

That's going from a very rusty memory and some details could be quite wrong. I was about 14 when I looked that up (7 years ago).

Ah...so the electrons moving in the tube creates induction, meaning higher voltage?
#9
Here is some more stuff to read.
Quote by lizarday
oh yeah? well larry king the slayer guitarist owns bc rich guitars. (i think)
#10
i did a physics assignment on it myself, i dont want to read it back to you but i found wikipedia very useful. Just look for the main points as despite all the big words and details they're a pretty simple system.
#12
I've read alot now and I have really understood most of it. the schedule Sin City Sid linked to, has a Triode/Pentode switch near the output. Why do you wanna switch between a pentode and a triode? The only difference is that a pentode has more grids and electrodes, right?

Thanks!

(Click on his link and then the left file, or look at this):

#14
I could be wrong but looking at the schematics it looks as if kills some of the power on the plate and giving it the ability a certain power output wattage or another output depending on switch position.
#15
Quote by VikingMetalhead
I understand that a cathode and an anode are the different sides of a diode.

"In a vacuum tube or electronic vacuum system, the cathode emits free electrons. Electrons are extracted from metal electrodes either by heating the electrode, causing thermionic emission, or by applying a strong electric field and causing field emission." "The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air. When hot, the filament releases electrons into the vacuum: a process called thermionic emission. The resulting negatively charged cloud of electrons is called a space charge. These electrons will be drawn to a metal plate inside the envelope, if the plate (also called the anode) is positively charged relative to the filament (or cathode). The result is a flow of electrons from filament to plate. This cannot work in the reverse direction because the plate is not heated and does not emit electrons."

Shouldn't this mean that the electrodes are released in the cathode, out in the tube, and then return to the positively charged anode? Why does the charge in easy words amplify?


Ok, good passage to quote, but it doesn't tell you the whole story. Vacuum tubes have 2 very important features - 1) Non-linear response and 2) (in triodes and higher) a small voltage can control a much bigger current. In audio terms, these are the most important things about tubes.

The reason why they have a very non-linear response so to do with the way the electrons are emitted. A certain filament current is required to heat the cathode enough for thermionic emission, which is typically quite big. So you've got a massive flux of electrons out of the cathode, but only a small +ve voltage at the anode, the electrons have got nowhere to go, so it builds up something called a 'space charge', or a region of space with a significant local electric charge. Now, because electrons are all negatively charged, they repel each other, with a net result that they get constrained and it becomes more difficult to draw them towards the anode. So to get the charge flowing, you have to massively increase the potential, until the whole charge flows to the anode - which results in a saturation effect. If there's a net as well, you can bias the tube to control how large you want the voltages to be before it 'turns on' and how much of the distortion from the saturation you want to be able to pick up. Very tunable, very cool devices.

The second point is what's really important in amplification. All amplification is based around this principle, a small voltage controling a large current. In the case of a triode, the input signal is fed into the net, and small variations in that signal will cause larger variations in the signal arriving at the anode, which is the signal used for output.