I think that Gurumurthy tries to do the squaring of the circle!

Already, a linear supply of 0 to 30V with a max current of 5A, this represents a dissipation of 35V x 5a, that is 175W, it is totally unrealistic.

You will have to use a way to reduce dissipation as a pre-regulator or switchover of transformer taps.
And in addition, he wants a simple circuit ....

I think he should open a topic in the "beginner" section and start by studying a little bit of electronics first.
It is clear that he does not know what he wants, nor if what he wants is possible or not ...

There is no shame in being a beginner, we are here to help them, but at a minimum, the person should realize that he is a beginner and to have enough modesty to recognize it.