The 318B is a re-engineered A . It gives up nothing in return . The A isn't in the same class as the B . The ext. is exactly the same and it uses the same tubes . But the B was electronically changed to maximize the very thing the A was lacking . Highs and lows . The mids on the A are incredible . The B has the same mids and more extention on both ends . And it's mere 18 wpc energy and drive is equivilant to around 100wpc ss.