High Quality Content by WIKIPEDIA articles! THD Electronics, Ltd. is a manufacturer of vacuum-tube guitar amplifiers and amplifier accessories, and is located in Seattle, Washington. It was founded in 1986 by President and CEO Andrew Marshall. Although it specializes in hand-built, vacuum tube “boutique”-style amplifiers, it also manufactures the “world’s best selling power attenuator,” the THD Hot Plate. The company is well known in the boutique amplifier market, and is often credited with the creation of this market in the United States. THD’s line of products has stayed relatively small despite its 22-year history as a company. Of its amplifiers, THD currently makes three: the UniValve, BiValve-30 and Flexi-50.