This is the latest 6550EH tube for home audio amps from Electro-Harmonix. The Electro Harmonix 6550-EH tubes have excellent linearity, power handling capacity and heat dissipation. Four-pillar construction and mica spacers help maintain a rugged mechanical reliability. Classic tone is sustained at a prolonged, high output. A new leaded glass compound is utilized to maintain vacuum integrity, balanced performance and ensure long life.