Electro Harmon 6973 is available for purchase as matched singles, pairs, quads.  Finally, a genuine 6973 tube at an affordable price, not rebranded "close" tube.  Electro-Harmon tubes are all newly designed and are of excellent quality. Many OEMs relabeled Electro-Harmon vacuum tubes in their amplifiers. If you great sounding tubes a very reasonable price, Electro-Harmonix tubes should be on your list