Hi,
Your machine was made by Gunter Wulff Gmbh, in 1968, the company was bought by Bally in 1972, in 1960 the company assembled all of the Sega Bell machines for Marty Bromley to operate in the U.S. military clubs in Europe. I have attached various pictures of the company, including one of my late fathers stand at the 1960 London Trade Show, the lady in the picture is my late mother, also pictures of the Sega Bell that was assembled in Germany, in my autobiography I have more than 20 pages relating to the company, Hans Kloss a past president of Gunter Wulff became president of Bally Gaming in Las Vegas in the early 1990's, he is a friend of mine since the early 1980's when Bally produced one of my machines under license in the Gunter Wulff factory in Berlin.
Your machine is a fine piece of engineering, but operates on an high voltage, so be careful, sorry to tell you it is not a very collectible piece, but if you google Gunter Wulff on the internet, I am sure you will find a web site for German collectors, I would just keep it for a decorative item, no value here in the U.S.
Freddy Bailey