The invention of the transistor has made vacuum tubes obsolete in virtually all applications, except for one major exception. Musical instrument amplifiers in general and guitar amps in particular have proven to be one of the last refuges for tube-based designs. No one can argue that modern solid-state amplifiers are efficient, inexpensive, and capable of sounding great too. However, vacuum tube amplifiers, which we will simply call “tube amps” from now on, have a certain sonic quality that really can’t be duplicated with transistors or op amps. This chapter introduces some basic vacuum tube design and analysis methods, as well as several practical guitar amplifier circuits, construction techniques, and parts suppliers.