Amphead stocks a deep inventory of premium tubes — JJ Electronic, Sovtek, Tung Sol, and more — and takes a more methodical approach to retubing than most. Preamp tubes are selected by ear for each specific position, output tubes are biased by both current draw and crossover distortion, and every new tube is burned in to catch factory defects before they cause problems. All tubes purchased and installed at Amphead carry a 3-month guarantee.