Tubes versus transistors in electric guitar amplifiers

Although transistors have replaced tubes in most applications, the tube remains the dominant force in electric guitar amplifiers, representing millions of dollars in annual sales. This is due to the musician's insistence that tubes "sound better". Advertising literature of some manufacturers claims that their solid state circuit has the tube sound, while other manufacturers insist that the tube sound can only be obtained with tubes. It is the purpose of this paper to identify the electrical parameters that define the differences in the perceived sound of tube and transistor guitar amplifiers.