Very good question bor, I predict that almost all receivers are built-in BEC! If not, good project for me to check all my fm, am and 2.4 receivers to see if they have the BEC or not!
Normally if I am using a ESC, I have no problem to plug it in the receiver, no other plug like Tamiya 101 or 104. So I assume that plug even it is an additional plug in receiver, it should be 6v. Just common sense, am I right??
Because I am playing my Pumpkin and Baja Champ with 101 ESC and 2s lipo for quite a long time, no problem bor!!!!