Zeiss SL-120 New Style converting to Old Style Electronics

This new style has a circuit board and corresponding smaller diameter rheostat. If you can find an old style rheostat with the bigger diameter post you can drill the cover to accommodate the larger diameter rheostat and connect wire according to the simple non-circuit board layout.
I used a step drill bit to enlarge the hole and drilled another indention with a drill bit to make space for the stop to lock in.
Dry fit your parts first to make sure it's going to work before you commit to drilling out the rheostat cover. ☺
I used a rheostat from a Zeiss 20SL which also is 6V 20W. If you use a different rheostat, make sure it will work with your 6V 20W configuration.