NOTE: – these varic devices ARE NOT specifically designed for use with guitars but for electronics engineers who need to use different and varying voltage supplies to test and design electronics equipment. However – like Eddie Van Halen used his – if you know what you are doing with electronics you can use variacs with guitar amps to drastically alter the sound by running it at different voltages. Please note: 1) they may shorten the life of guitar amp tubes and valves or even blow them if you use them a variac wrongly 2) using this device wrongly can blow and ruin your amp! 3) you are dealing with voltages so there is always risk or electric shock and death if you use wrong voltages or go poking about inside your amp or the variac. Even though Eddie used these as a amateur they are for electrical professionals ONLY!