Burned In for maximum stability.
The new JJ 6CA7 is a more classic version of the EL34 tube. It has a large bottle and big, warm sound. 6CA7 is a beam power pentode with octal base. It can be used in most EL34 amplifiers. Even more powerful than KT77, and very similar to 6L6 sound. The 6CA7 provides a typical American sound.