I recently picked up a used Ray Samuels Raptor from head-fi, which I love. I was researching possible tubes to experiment with and I noticed that there is one called Raytheon 5687WA. I currently have some GE tubes in the amp and they're designated 5687WB.
I'm new to tubes and wondering if someone could help explain the WA-WB difference or has any other advice. It doesn't appear to be the most common tube type but I've heard good thing about the Tungsols.