In the circuit above a Class AB amplifier (this is one also called Class A+AB) can be seen with Q1 and Q3 used to get the current biasing voltage for Q2 and Q4. transistors Q2 and Q4 become hotter and hotter and requiring more and more current in the actual built circuit and in the end it reduces the output signal to 0. Are there easy changes that can be made to prevent this from happing?
The power supply gives 10Volt.
EDIT: As some of you noticed, there's was no resistor shown at the output in the figure above, but it is added now.
Best Answer
It appears that you are using the B-E junctions of Q1 and Q3 to provide the bias for Q2 and Q4, respectively. This will only work if the four transistors are coupled thermally so that they are all at the same temperature.
Also, the value of 39 for RES1 and RES2 is ridiculously low. What are the operating voltages of this amplifier?
Overall, this is a very poor circuit. Where did you get it?