Common Electronic Components Overview

Capacitor

Capacitors are used to store and release an electrical charge. They will block DC while passing AC. They are frequency-dependent devices, which means that their capacitive reactance, or "effective resistance" to AC increases as the frequency gets lower. Long ago they used to be known as a "condenser".

• Bypass cap

A Bypass cap is a capacitor that is connected from the power supply to ground. It "bypasses" the AC signals to ground, while passing the DC supply through. This is used to make the DC supply rail "clean", or free from AC noise.

• Coupling capacitor

Used in guitar amplifiers to block the DC plate voltage of the previous stage, while passing the AC guitar signal on through.

Diode

Controls the flow of electricity, as it only allows a current to pass in one direction. They are commonly used to convert AC to DC current by blocking the negative part of the AC signal, or, if they are reversed, they pass only the negative part and not the positive part. This allows them to be used to generate a positive or negative DC supply. Diodes are also commonly called "rectifiers" because they rectify the AC voltage, however, the term "rectifier" is usually reserved for diodes used in the power supply section of an amplifier, while "diode" is generally used in small signal, or low power applications, such as clippers.

• LED

LED is an acronym for Light Emitting Diode, a semiconductor device that emits light of various colors when an electric current is passed through it. LEDs are typically used as indicators, but occasionally are used as clipping diodes because of their larger forward voltage drop when compared to a standard silicon diode.

Inductor

An inductor is also known as a "choke." A choke is often used as a power supply filter. Inductors use a circuit element consisting of a coil of wire would on a core material made of ferrous or non-ferrous material. An inductor resists changes in the flow of electric current through it, because it generates a magnetic field that acts to oppose the flow of current through it, which means that the current cannot change instantaneously in the inductor. This property makes inductors very useful for filtering out residual ripple in a power supply, or for use in signal shaping filters.

Resistor

A a circuit element that presents a resistance to the flow of electric current. A current flowing through a resistance will create a voltage drop across that resistance in accordance with Ohm's law.

• Potentiometer

Also known as a "POT" for short, a potentiometer is a variable resistor. With three terminals, two across which the entire resistance appears, and the third terminal with a wiper arm that moves to a different spot on the resistor as the shaft is turned. The resistance between the wiper and one end terminal gets smaller while, at the same time, the resistance between the wiper and the other end gets larger. This allows the potentiometer to be used as a variable voltage divider, for use in attenuators, such as volume controls or tone controls.

Transformer

A transformer changes the level of AC signals, or the impedances of circuits. They consist of a minimum of two coils, the primary and the secondary, wound on the same core. An ideal transformer has no losses, it merely steps a voltage up or down in proportion to the turns ratio between the primary and the secondary. This is useful in converting the voltage from a wall outlet, typically 120 or 240 volts, into a higher voltage for the tube plate supply, typically 400V or more, and a lower voltage for the tube filament, typically 6.3 or 12.6V. The transformer will also "reflect back" to the primary the impedance which is connected to the secondary, in proportion to the square of the turns ratio. That is, if you have a 20:1 transformer with a 16 ohm impedance connected to the secondary, it will "look like" a 6.4K ohm impedance on the primary side. This is useful in matching the plate of a tube, which is very high impedance, typically on the order of several thousand ohms, to a speaker, which is very low impedance, typically on the order of 4, 8, or 16 ohms.

Transistor

A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals. Transistors are the basic elements in integrated circuits (ICs), which consist of very large numbers of transistors interconnected with circuitry and baked into a single silicon microchip or "chip."