The BGA Velectrik derailleur depicted has:

• Curved pulley cage plates.
• A round tension pulley with no teeth.
• A 'chain-catcher' at the tension pulley.

(Source gallica.bnf.fr/ Bibliothèque nationale de France)

• Publisher: L'Officiel A.C.M.
• Country: France
• Date: August 1938
• Derailleur brands: BGA
• Derailleurs: BGA Velectrik