I was cleaning a 1979 Austro-Daimler with a single-pivot Suntour derailleur and I decided (in a fit of stupidity) to remove the bolt that holds the cage tensioner spring, and I removed the derailleur from the spring assembly.
Well now that it's nice and clean, I don't know how to tension the spring.
It's not like the newer ones that use a ribbon spring. It's got a coil spring that has a tab that seats in a post that is like a king nut.