The Svetlana 6L6 Medium tubes have the classic Sylvania STR sound.
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 must be driven harder to yield a distortion which typically ends up being thinner and warmer sounding distortion, while medium-rated tubes fall in between.