This vintage engraved vacuum tube is a DeFOREST AUDION 427 TRIODE model, known for its exceptional quality and performance. Tested for functionality, this unit is sure to provide a reliable boost to your vintage audio and video equipment. Made in the United States, this tube is a valuable addition to any collection. Selling as used does show signs of age and measuring 900 microhomos with a minimum of 650, tested on calibrated Heathkit TT-1 tube tester. Missing original box Please see photos any questions please ask. Thank you