Sovtek 12AX7-WA, 12AX7-WB Review.

I've grouped these two together because they have essentially the same sound. The only noticeable difference between the two was a bit more gain from the WB model. These tubes are rugged little brutes, and that's probably why they are OEM components for many major amp makers. Both tubes could be whacked with a stick at full volume and not show much in the way of microphonics - but DON'T DO THIS AT HOME, as it is often a destructive test for tubes. They don't have the best sound in this type, being prone to the occasional pop or tick. The sound quality lacked any real character but was acceptable. If the budget is tight, their affordability will be attractive. Also, keep in mind that many amp designers design the equipment to sound best with the tubes they will use in production. I have a friend that claims his amp only sounds right using Chinese pre-amp tubes, but your mileage may vary on this issue. If you like the Sovteks then go for it, particularly if you will use them in high gain applications with lots of effects.

Information from thestoretube.com