The 7025 market is in short supply, and the 12AX7 is a common product, which is generally used in places with low requirements for noise and hum; 12AX7A is a product that has paed 100% humming, noise and microphone effect inspection on the products produced. It is suitable for the first tube with extremely high requirements for signal amplification at the previous stage. Its on-machine qualification rate is very high. 12AX7B is an improved version of 12AX7A. After the improvement of this tube, the microphone effect of the original 12AX7/A has been completely solved. This item can be exempted from inspection. In addition to testing various parameters, noise and humming are also fully inspected, Because the test items have changed, it is named 12AX7B. The length of the tube core of the 12AX7-III electronic tube is shorter than that of the 12AX7B. Because of its short tube core, the poibility of its vibration with music is also reduced. Therefore, its anti-microphone effect is more obvious, but its amplification performance and gain are also relatively small. It is a good choice for models with low requirements for amplification and sensitivity. EL84 is also an improved product. Compared with 6P14P, it has higher withstand voltage performance and higher output power. Some people evaluate it as a very good EL84 at present, which is mainly used for bookcase low-power audio and computer peripheral audio equipment. The 7025 is a high-grade preamplifier developed by Dawn, which can directly replace the 12AX7B. However, the control of its micro-noise, sound and microphone effect has almost reached a surprising level