12BH7 Tube is capable of driving good amounts of current with low distortion. This makes it ideal as a driver for power tubes in modern audio amplifiers. Current production 12BH7A from Electro-Harmonix is a direct replacement for any 12BH7 and 12BH7A tubes. JJ ECC99 is a compatible driver tube. Any tube product and certainly any tube product with large output transformers will sound better after it has warmed up for about 30 minutes. However, should you be considering it, the value of leaving the amplifier powered up constantly must be weighed against extremely shortened tube life and, should anything go wrong while the amp is unattended, say, a tube spits loudly as it burns off some ... A Comparison of Current Production 12AX7 Tubes. RCA and Sylvania first introduced the 12AX7 to the world in the late 1940s. Today, it is by far the most common preamp tube used for electric guitar amplification and there is an almost overwhelming supply of current production options to choose from.

Special Quality (SQ) version is burned in and tested carefully with our custom tube testers. We do not just test plate current, but test and match tubes in actual audio circuits.