Vacuum tubes are the heart and soul of any amp. There are three basic types of vacuum tubes for amplifiers: Preamp, Power and Rectifier. All of these tubes generate the tone and power of your amplifier. You can fundamentally change your amp’s performance and tone by simply changing your tubes.
There are multiple factories that produce vacuum tubes and various companies that screen, filter, and re-brand tubes. This gives you a variety of options when trying to decide what tube to use.