Greetings Folks...
I already said about my problem in Buck board. I successfully resolve the problem. I connect the UBEC (Buck Board) in Battery port in Receiver. It works well, and the signal condition was very good. When I connect the servos in receiver, My TX warns me low voltage warning of RX. when I Plug out the servos, again signal strength  is very good. so, I finally fixed the voltage is enough, but current is very low. That's why the servos aren't work. so, I need a another power source. I connect 4 servos, so i need atleast 2-3 Amps. I saw 7805 transistor regulates the voltage of 12v to 5v. But I have a doubt, this transistor regulates the voltage, but what about current??. This is my biggest question guys. I'm also read many scholarly articles and visit many websites, they put 12v to 5v only. They didn't mention about current. That's why I'm putting this Thread in RCI. 
I attach a Pic of Circuit. Please give me your priceless suggestions to improve my knowledge and project.
Thanks in advance....

Refer the datasheet, it can differ from brand to brand.

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Thanks Bro....