Thank you, hansbe, LvW.
I was simply playing around when I drew that block diagram. Truth be told once again (although I have already told it in first post above) that I have never used an amplifier or an oscillator. You can change some parameters such as frequency, you can change amplification gain to any other number (the gain used by me is "2"). If someone of you have MultiSim, then can you build that circuit up so that I can understand its working by asking follow-on question? Thank you.
Best wishes
PG