This training or practice key was made by A. Chabot. Chabot also made the Dyna Manitone and Dyna Maniflex. A.Chabot was Dyna's founder. He began his career working for Georges Pericaud, the famous wireless manufacturer in 19Ø9, where he designed the first crystal set for them. After WWI, Chabot became president of Pericaud. In 1921 he founded "A. Chabot" with trademark "Dyna." The company produced various radio equipment for both amateurs and professionals. In ads from 194Ø to 1977 the address was listed as 36, Avenue Gambetta, PARIS. The company founded in 1989 due to financial reasons. The Dyna trademark can be seen on the black base, on the left of the contact nearest the knob. According to previous owner (Wyn Davies), the Dyna training keys were for civilian use only from 1938 until 1960.
Thanks fo info to Herman VK2IXV
(non original knob)