The Tube Amp Doctor 6550A-STR is built and performs to the same standards as the highly sought after GE 6550A. TAD has meticulously designed the plate material to be as strong and pure as possible resulting in an exceptionally stable, consistent, and reliable 6550. The TAD 6550A features a thick straight glass envelope, a metal base, and an authentic triple getter. The frequency response of this tube is remarkably balanced and smooth. Transparent natural lows and thick rich mids with silky highs make this an excellent tube for HiFi equipment as well as classic bass guitar amplifiers. The Tube Amp Doctor 6550A-STR offers outstanding performance in all applications. This tube is matched for both plate current and transconductance. The TAD 6550A-STR also passes all of the tests required in the Premium Selection process.