Nitty Gritty
In previous decades, transistors offered guitarists cheaper and lighter amplifiers, and today digital amplifier modelling technology can achieve astonishing sound quality. But huge numbers of guitarists remain addicted to the bottle – or thermionic valve if you prefer.
Thermionic valves come in many forms and their names tell us how many working parts are contained within that glass or metal enclosure, not including the heater. The simplest form of valve is the diode, which only contains an anode and a cathode. A heated cathode releases negatively charged electrons into the vacuum, hence the terms ‘thermionic emission’ and ‘thermionic valve’. With AC voltage from the power transformer connected between the anode (aka plate) and cathode, current flows through the valve when the AC is in its positive phase at the anode because it attracts the electrons. When the AC is in its negative phase, no electrons are attracted to the anode and no current flows.
With current flowing in one direction but not the other, diodes
