What Are Your Tubes Really Doing?

Let’s look at how tubes work and the role they play in turning our quiet, tiny guitar signals into sound. There are various types of vacuum tubes, but in the guitar amp world, three types are most common: rectifier tubes, preamp tubes, and power amp tubes.

Let’s start with rectifier tubes. As part of an amp’s power supply—the part of the amplifier circuit that makes the voltages the rest of the circuit needs to operate—rectifier tubes help convert, or “rectify,” the AC (alternating current) from the wall into DC (direct current). The amp’s power transformer only runs on AC, so it’s up to the rectifier tube to create DC, which is needed by the other tubes. (The filter capacitors are also part of the power supply, and these are needed to make proper DC from rectified AC, as well as a “choke” transformer.) The tubes that we use in this part of our amp are specialty tubes designed to do this one particular task and are not interchangeable with preamp and power amp tubes.

“The small guitar signal creates electrical movement on the screen of the tube, which causes movement on the plate, which gets significantly amplified due to its high-voltage potential.”

The preamp section’s job is to take the delicate signal from the guitar and amplify it to a level that can drive the output section. This is done in stages because of how small the guitar signal is, which is why we have many 12AX7-type tubes in our amps. Here’s how preamp tubes function: