[Arran]

Spider web style coils, that's a very interesting take on a variocoupler. If you think about it it pretty much does the same as a later volume control, it varies the gain by varying the coupling. I can't recall seeing such coils in a factory built set before, though there were probably other sets sold that did, I think the last set I saw with spider web coils was a home brew, and I think that they were fixed.
Regards
Arran