Problem with a class AB amp
I see a few problems.


As Jippie says, C2 and C3 are reversed. The collector of Q1 will be biased somewhere between +50V and ground. The bases of your output transistors should be biased somewhere close to ground.
Your preamp biasing looks a little suspect. With a minimum beta of ~75 (from the datasheet), Q1's collector would barely get down to 10V below the supply voltage. If you want a 10V output swing, that's not a lot of room. The transistor you have in the circuit right now might work, but it probably won't be reliable.
You might need more than one diode between the output transistor bases. Your diode voltage is going to be ~1V, but your Vbe drops will probably add up to ~1.5V.


Finally, make sure you stay within the safe operating area of the TIP31s (from this datasheet):