Link circle and rail revolve diameter/radius

Hey folks, this is my first post here!  I am having a blast with Grasshopper but am running into a bit of a wall on my first real world job.

 I would like to use one slider to increase the radius of a circle and simultaneously move a curve that I am revolving around this circle.  I am attaching a screen shot of the definition as well as the shot of my input curve and resulting surface.  

I have tried to integrate a Vector component in the Y axis but am having difficulty linking the two functions (curve radius + move in Y axis).

This is probably super simple but it has me stumped so far.  Any help would be much appreciated! 

Thanks!