ECC 99 was developed as a driver tube for JJ 300B. ECC99 delivers excellent linearity with very strong drive capability, making it suitable for driver application for DIY audio projects.
ECC99 is similar to 12BH7A, and is a drop-in for most applications. Please note that on some amps, 12BH7A is used in power supply circuits and ECC99 is not a drop-in. If you are not certain, please check with the amp manufacturer first.