Art Audio only sells Grade A Tubes from Sophia Electric.
Sophia Electric Princess mesh plate 274B and rigid plate 274B tubes have been widely praised as the best sounding rectifier tubes ever made. However there is a catch - the first capacitor after the rectifier tube needs to be small. The max value allowed for the Princess 274B mesh plate is 4uf, or 8uf for the Princess 274B rigid plate. But for a typical 300B single ended amplifier, it is usually larger than 8uf. To overcome this limitation, Sophia Electric came out with a newly designed Aqua 274B rectifier tube to raise the limitation from 8uf to 47uf. This Aqua 274B can directly replace 5U4G in most amplifiers with great sonic improvement.
This tube usually ships within 2-4 business days.