An affordable tube in 3 grades for different levels of distortion.
The Tung-Sol 5881 is a very reliable, general purpose power tube much like the 6V6. These tubes are available in different grades depending on how much distortion is desired. Matched set.
Soft, medium, and hard style descriptions refer to break up modes of the tube for an overdriven guitar signal. Soft-rated tubes break up easier and have the least headroom, yielding a heavier, harder distortion. In comparison, hard-rated tubes are harder to break up and have the most headroom. Medium-rated tubes fall in between.