[sdiy] Spring Reverb

[rob]

This weekend I found a quite destroyed Peavey Model 400 preamp lying inside a shopping cart in the rain next to my house.  Of course I couldn't resist dragging it inside for a look and I found inside an 18 inch accutronics spring reverb box in great condition.  It has two little springs inside and no real visable serial number.  So my question is, what is the easist circuit I can build around this to turn it into something functional?  I've looked around the net for scematics, but I don't quite grasp some of the more complicated scematics.  How do I measure the input impedance?  I don't need this too sound like a million bucks, I'd just like it to do something.
Thanx,
Rob