For Cayin and other Chinese 300B amplifiers designed under 220V AC 50Hz, I would recommend Sophia Electric Carbon Plate Princess 300B tubes for the following reasons:
1. Sophia Electric Carbon Plate Princess 300B was the top of line model from 2006 to 2010. It must be that good to be the flagship model for 4 years.
2.At $600 per pair is a great buy for its sound and long life span.
3. Very different sonic style compared to your mesh Princess 300B tubes. It is the Second best sound only to the Royal Princess 300B from Sophia Electric
4. Sonically, it would transform Cayin and other Chinese 300B amps to another league
5. Magic mid range and the best bass extension for a 300B tube. The high frequency is super smooth.
6. Extra dissapation margin over the 40W rating and still a WE format tube with traditional 300B electro and sonic characters.
WA