I'm a former electronics technician, recording studio owner, life-long hi-fi guy, hobbyist speaker designer guitarist and singer. These days I'm a computer professional, but I've never lost my interest in electronics.
 
I'm of the opinion that there are a lot of misconceptions about how amplifiers work. In this blog I'll attempt to explain as much of what I know (and sometimes what I think I know) about what's going on inside these devices that put the electric in guitar.
 
We'll cover a lot of ground. I'll try to keep it as simple as possible. There will be some theory, some history and, on occasion, some very simple math. I'm always open to questions and corrections so send me a PM if you have something to say.
 
Up first: Valves: Lee DeForest's gift to the world 
 
 In the U.S, we know these devices as tubes. More specifically, the correct term is thermionic emission tube. But I've come to prefer the British term valve because is succinctly describes what a tube does. And that's what most tubes are. They are, essentially, valves for electricity. 
 
All tubes work on the following principal. Inside the tube, there are two metal plates. These plates are separated by a space between them. All of the air has been removed from inside the tube leaving a vacuum. There's a heating element much like the one found in toasters. By heating the plates, a voltage applied to one of these plates will cause electrons to jump the gap allowing a current to flow. One of the plates is called the Anode and the other is the Cathode. One is positive and the other negative, in simple terms. Actually, as with so many things, it's relative, but for now this simple description will do.
 
What I've just described is a diode. Diodes are one way streets for electrons. Electrons flow freely in one direction, but can't flow in the other direction. If you have a tube amp with a rectifier tube such as the  5AR4, that tube is a diode. It's job is to convert AC current (which flows alternately in either direction) into DC current by blocking the current when it switches to the alternate direction so that all that's left is the current that flows one way.
 
Diodes are great. The 5AR4 is an essential part of an amp because it supplies DC current. But you can't build an amplifier using only diodes. Let's take a step back here and think about what an amplifier does. It takes weak electrical signals and makes them much stronger. How does this happen? The key is to somehow control a lot of electrical current with a very small one.  Here's where Lee DeForest comes in. He figured out if you stuck a terminal in between the plates, you could control the flow of current. He called his new tube the Audion. We know it as the Triode. The terminal in between the plates is called the grid. If you apply a small current to the grid, you can modulate the larger current flowing between the Anode and the Cathode. With the Audion, the electronic amplifier had arrived. It is difficult to over-estimate the impact of the triode on the world.  It made long distance telephone practical. It made radio practical. It made electronic computers possible. It changed the world.
 
That's it for this installment. What's coming up? All kinds of stuff.