You don't need an adapter. I run futaba servos with my JR equipment all the time. On the newer futaba plugs, there is a ridge off to one side. This is so you can only plug it in one way. Just cut this ridge off (with wire cutters) and plug the servo into the Jr transmitter. No problems. Just make sure you plug it in right. The colors are a little different, but they go together in a sensible manner (black to brown and so on). You will not have any problems using the futaba servos with your JR receiver.