<P> The most common approach to power attenuation is the' power soaker' approach . In a' power soaker', a portion of the power is absorbed by the power attenuator (which is placed in circuit between the output transformer and the guitar speaker), while the remaining portion of the output power is directed to the speaker . An example of a common type of attenuator circuit is the L pad . A variable L pad is a power divider circuit that is designed to operate with a load in such a way as to provide an adjustable level of power to a speaker while maintaining a constant load impedance on the amplifier . </P> <P> A different approach, using a Variac or a power scaling circuit, reduces the B+ supply voltage available to the power tubes thus producing power tube distortion at a reduced level such that all available output power is sent to the guitar speaker . The Variac method is not without risk, as the reduced heater voltage applied to the tubes can damage the filament and / or cathode if not operated within the manufacturer's specifications . In a power scaling circuit, by decreasing just the B+ plate voltage, the cathode bias and screen grid voltage decrease proportionately, while the filament voltage stays constant . However the term power attenuator may be a misnomer for this type of power control because lowering B+ voltage tends to increase distortion, whereas according to convention, an attenuator should not introduce distortion . </P> <P> Power Damping is a method of output level control that involves the phase inverter and a potentiometer . The potentiometer allows that stage to be overdriven at reduced output similar to a Post Phase Inverter Master Volume (PPIMV) control . </P> <P> A power attenuator can be either purely resistive, or mostly resistive and partly reactive . The original guitar amp power attenuator, the Altair Attenuator, was primarily resistive, used a rotary switch to select taps on a toaster coil with low inductance windings . Another early model, simply called' Power Attenuator' by Active Guitar Electronics, used continuously variable power rheostats . Other models, such as the Marshall Power Brake, add some electrical inductance or capacitance to the electrical load (including fans, light bulbs and coils). There is debate about whether reactive attenuators do a better job of preserving a guitar amplifier's tone . </P>

What does an attenuator do on an amp