I used the Gold Lion KT 88, SED winged "C" and Tung Sol 6550s in my ST-150. The Gold Lion's sounded wonderful but I had some reliability issues with them. Two of them went bad with somewhat under 1000 hours on them. The SEDs had great upper end extension but withthe speakers I was usning at the time, Vienna Acoustics Beethovens, they were a litlle light and loose in the bass. The Tung Sols were a little less extended and sparkly at the top end but had better bass authority the mids were about equal for the SED and Tung Sols. Both the SEDs and Tung Sols lasted two years or more without problems.
Right before I sold the amp last year SEDs were getting hard to find and Gold Lions were too expensive for my budget especially if they didn't have the reliability of the others. I defaulted into getting the Tung Sols and I was happy with them.
I found the Sylvania Gold Band 6201 in the 12AT7 spot was a great improvment over the stock tubes. Mullard CV 4024 were nice as well.
Right before I sold the amp last year SEDs were getting hard to find and Gold Lions were too expensive for my budget especially if they didn't have the reliability of the others. I defaulted into getting the Tung Sols and I was happy with them.
I found the Sylvania Gold Band 6201 in the 12AT7 spot was a great improvment over the stock tubes. Mullard CV 4024 were nice as well.