Steve and Raimey: as far as I know, it's a so called "Kontra-Einhakmontage", made in the 1970ies and 80ies by Kettner Germany. The only purpose probably was to offer something "New"... It was nearly the same as the Suhler Einhakmontage but offered for some less money. Functionally it was like the Original.

Cheers,
Wolfgang