When the tube stockpiles dried up in the 80’s, and before modern tube production ramped up, there was little available on the market except the Shuguang 12AX7A vacuum tube. These 12AX7 amplifier tubes have been in production for decades, and while the factory has changed locations over time the tubes have remained unchanged. Many amp companies have made this tube a stock component, two of the biggest companies were Peavey and Mesa Engineering. The design is interesting and unique. Two small dual triodes separated by an isolation plate and held in place with 3 mica spacers. These little 12Ax7 tubes are notable for their high gain. They tend to be a bit gritty and bright with a little more background noise than most. It’s the price for high gain. Most frequently used by hard rock and metal lovers for all of the reasons listed above.