Hello, Probably the reason the 3CX1500A7 hasn't been mentioned much as a replacement for the 4CX1600B is the cost of the tube. I think the 3CX1500A7 runs around $850.00 new for it, vs $200 for a new pair of russian 4CX800A's. Eimac is ridiculously expensive with their tubes. 73, Todd - KT0DD - kd7efq at aol.com "The race is over...THE RATS WON !"