Although this Shuguang 12AX7B vacuum tube is listed as a variant of the 12AX7A amplifier tube there is really very little difference to discuss. Physically, they look virtually identical. There may be a slight difference in the colour of the plate coating between A and B but that could have been batch to batch variation. For all intent and purpose this is a 12AX7A that has been screened to select the tubes with the highest gain and lowest noise. One thing that I will say about both the A and B, is that they really sound good for rock and roll. If you are having noise and microphonics issues with the A variant but want to keep the gritty attitude, then you should try the Shuguang 12AX7B before you move on.