A softer version of the older USA 6550A, with a nice distortion character. This tube has a distortion that is between a 6L6GC and a 6550A. In older Marshall's that have 6550's, this tube will give you more compression and distortion at lower levels than the other 6550 offerings. This tube is terrific in Class A amps such as the GT Solo Single when you want to have a lot of output for smaller live venues. Many people prefer these in some Marshall amps where more clean headroom and output is desired. Price is for a matched quad.