No, I am afraid it doesn't quite work that way. Amphetamines stimulate everyone. The reason they can be effective in the treatment of the symptoms of "ADHD" is because they promote concentration, attention, reward for succeeding etc. I am not going to say they don't calm you down, because I can very much believe that, but they are still stimulants, not any sort of tranquilizer for anyone. As to why you can't achieve long periods without sleep using amphetamines, I would guess it is because you have been using amphetamines for your "ADHD" on a daily basis (or even less frequently) for some time now, and you have quite the tolerance, such tolerance that warding off sleep with a normal dose of amphetamines may not be possible.