Art Audio only sells Grade A Tubes from Sophia Electric in matched pairs or quads.
The glass enclosure was from the Princess 206 tube for its unmatched sonic beauty. The shape of glass enclosure does make a major difference. Just thinking of violin's shape, if it gets changed to triangle, the sound character of violin will change for sure.
Sophia Electric engineers have conducted many hours of auditions and comparisons. In the end the current shape of Princess tube glass enclosure is the most preferred choice sonically. It has more volume and more curved than the old ST. It is not the old ST came back rather it is a carefully crafted, researched new 300B model. The result is a 300B mesh plate tube with super clarity, low distortion and out of this world mid range fullness and liquidity. High frequency extension and sweetness is the first thing you would hear.
True 300B standard:
This is a true 300B tube that is 100% interchangeable with the popular Sophia Electric globe shaped 300B mesh plate tubes and Western Electric 300B tubes, as well as current production Chinese/Russian 300B tubes (with WE 300B standard).
Distribution and availability:
It is important to note that the S.E.T. Princess 300B mesh plate tube is proprietary product of Sophia Electric and exclusively available through Sophia Electric and their select Authorized Retailers.
These tubes usually ship within 2-4 business days.