Made in USA by Bendix Redbank specially for the US military missile programme. These gold pin valves, sporting black anodes, triple mica along with a red Bendix logo, ceramic insulators, D-getter, gold grid wire, Nonex glass are suitable for acceleration up to 500G!!!!!!!!! - and are rated for a 10000 hour life
As a substitute with socket change or adapter, superior to Telefunken or Amperex EL 84 / 7189. These tubes have excellent imaging & detail with extended frequency response. Believed by some to be one of the finest miniature medium output power pentodes ever made.