Tube Amp Doctor is a German company specialized in electron tubes and related components for musical instruments and audio amplification. TAD is closely cooperating with all of the few existing tube factories. TAD techs, who are all active musicians, have been developing processes to test and secure the quality, consistency and reliability of TAD tubes. TAD STR tubes (Special Tube Requirement) are produced to exclusive TAD designs and strict specifications. TAD tubes get evaluated, tested, approved, selected and finally matched, labeled and boxed. All tube quality control and processing is done at the TAD plant in Germany. Every single tube has passed stringent listening tests to ensure the finest selection of premium quality tubes available on the market to support your music.