Now I see where the problem is. I was thinking of connecting the input to ground instead...
I think that I started to understand why the input should float somehow.
I am afraid I am going to waste your time MrAl.
Albeit dated, I recalled the UA78S40. IIRC, it is adjustable (divider is accesible) prety much as the MC34063. Expensive but both available locally.
In few hours I am traveling some 720 Km to the place where I grew up, to meet my classmates after just 50 years. And precisely THAT girl will be there!
She was beatiful..and still IS.
In the intervals, some datasheets and ANs have to be read. Gracias.