The Answer for my Xiang Sheng 728A preamp
The tubes that came with the unit were, in a word, lousy-ok bass, mid range and treble was listenable but keep you wanting for overall better sound top to bottom. I tried the Mullard 12AU7 and found them to be an improvement in the sound. I saw Denny L's comments and found he had the same desire for better sound top to bottom that I had so I thought I'd give the higher priced Gold Lion custom tube a try and found that the extra expense was worth every penny. In all areas, the bass was stronger and more extended, the mid range had more layers of depth and more focused, and the top end was more precise and extended without being harsh or hard. These Gold Lion premium tubes will be my choice for replacements for when the time comes. I recommend this tube very highly.