The purpose to this short post is to explain how a vacuum tube (electronic valve) works in no nonsense, straightforward terms. Here goes… Now, we all understand how a flashlight works. When it’s switched on an electrical current (electrons) flows from the battery through the thin metal wire (the filament) inside the glass light bulb causing the filament to heat up and emit light. Light is actually composed of particles called photons, but what you may not be aware of is that the filament is also emitting electrons too. You can’t see them, however if another, positively charged, metal electrode is placed within the glass bulb, they will flow towards it. This device is known as a ‘diode’ and current can only flow in one direction from the negatively charged filament (the cathode) to the positively charged anode. The quantity of electrons reaching the the anode can be controlled by adding a third electrode (the grid). Tiny voltage variations on the grid, for instance the output from a guitar pickup control a much larger current flowing to the anode. This device is an electronic valve, a ‘triode’, and can be used to amplify small signal voltages to make them bigger and that’s what makes rock ‘n’ roll possible!