Let’s talk about another tube stage that is common in Marshall amps but isn’t a gain stage, the cathode follower. Take a gander: This looks familiar, but different. The guitar signal enters pin 7 of V2 and exits pin 6 as a standard gain stage. This time, the signal next enters directly into pin 2 (note there isn’t a coupling capacitor to block DC.) Pin 1 does not have a plate load resistor like other gain stages. High voltage is placed on both pins 1 and 2, forcing the signal to go through...

Now might be a good time to talk about coupling capacitors. They connect different circuits together by blocking the high voltage DC but allowing your AC guitar signal to pass through. Just like the tone stack capacitors, the choice of capacitor value will effect the frequency range allowed to move on to the next stages. C12 .022μF below is an example of a capacitor used to connect the V2B gain stage to the rest of the circuit. Let’s start talking about gain stages that have a more distorted...

Are you strapped in? Let’s look at a common 12ax7 tube gain stage. This is found in many guitar amp circuits. Let’s continue where we left off, as the signal path from the previous section enters pin 2 (the control grid) of the V1A 12ax7 tube. Looking at the image to the left, the role of the 12ax7 type vacuum tube in this circuit is to take your tiny signal going into pin 2 and have it come out of pin 1 much much much bigger. Much bigger. Bigger than you think. 100 times bigger. We call that...