What you have is a Thunder Tiger Raptor V2, with a OS 50SX and a Curtis Youngblood Muscle Pipe (muffler), JR DS821 servos, a Futaba GY401 gyro controlling a Futaba S9254 servo for the tail, and a Spektrum AR7000 DSM2 7-channel receiver, Maverik carbon fiber blades, and some upgraded parts on the tail. Most everything looks pretty good EXCEPT for the DS821 servos. JR (Horizon Hobbies) did not reccomend using these on any heli bigger than a .30 size. Something to do with the geartrain/susceptibility to vibration. Give Horizon a call and ask them about the servos. If you want to keep the receiver a good transmitter to start off with would be a Spektrum Dx6i. You can usually find a good used one on Ebay or the for sale forums (rcuniverse, helifreak, runryder) for under $100. You can find spare parts almost anywhere (
http://www.rcheli.com/ (you can also download a manual from them)
http://www.amain.com/rc-helicopters/c2?fb=41&lg=fb0. The raptor is a good flying heli, and very tough. You will find it a lot more stable than your small helis. Try to get some help from someone who know how to tune up the engine if you're not familiar with nitro operation.