I'm also thinking about the 21AWP4 as a replacement.
it is NOT a 70 degree tube but a 72, not sure if that will matter or not, but ETF has one, it IS magnetic focus, and has a screen size close to the 21ep4b, I'm really not sure when it comes to finding a sub for these things.
electronically, it looks the same, if it WON'T work due to the diff in angle I will go with the first choice of the 21xp4.
