Class AB amplifier BJT operating point question
"Is it possible to get same output (18Vpp) if we change operating voltage to 0-12Volts?"
- No, because you can't get a voltage swing larger than the supply voltage in such an amplifier; it is usually slightly lower than the supply voltage.
Using 12V, you would probably get about 10.8Vpp at best, due to the base-emitter voltage drop on the output transistors (Vbe).