Internal impedance of Class AB amplifier?

This was a challenge problem that my instructor gave. Here is what a class AB amplifier looks like:

I've looked everywhere to find out about internal impedance but I got nothing. This is the problem I'm trying to solve:

Determine the maximum peak to peak signal that can be applied to a amplifier and the efficiency rating or nstage for the amp. Assume the amp is driven by a sine source and has an internal impedance of 600 ohms.

Given:

• $$\\text{hfe} = \text{hFE} = 100\$$
• $$\V_{be} = 0.7\$$
• $$\E_s = 32.093~V_{p-p}\$$ at 1 kHz
• $$\R_L = 8~\Omega\$$
• $$\R_1 = R_2 = 1~k\Omega\$$

I've tried all that I've been taught so far. I took the internal impedance as $$\Z_{input}\$$. Then, I used $$\Z_{input}\$$ and $$\E_s\$$ to find $$\V_{in}\$$, since $$\V_{in} = V_{out}\$$ is the voltage at the load. Finally, I used that answer to find the efficiency as $$\P_L / P_{dc} \cdot 100 \$$.

I calculated an efficiency over 200%, which must be wrong. What am I doing wrong?

• You will notice that if you put some more care in writing the question it will receive much better feedback. I've edited it as an example. Commented Oct 6, 2014 at 12:56
• Sorry I was in a rush for class an this is my first post so forgive me for my negligence but your advice is well noted. Commented Oct 6, 2014 at 13:00
• I've only done a few push pulls, but those caps on the input bother me. Will this work? Commented Oct 6, 2014 at 13:35
• Sorry I took a look at my circuit and u r right there is no caps just what you see above since I changed it. Inputs signal connects directly to circuit with no Rx resistor but I still don't understand how an internal impedence affects the vload or how much voltage the amp can be put through Commented Oct 6, 2014 at 14:58
• What is Es, and why is it specified to 5 significant digits? It seems it might be the input voltage, but that doesn't make sense since that is what you are supposed to solve for. Commented Oct 6, 2014 at 15:05