This Bulgarian key is marked on the top of the cover with 'G. Damjanov' and 'Razgrad'. G. Damjanov was the name of the factory and Razgrad is the city in which it was located. George Parvanov Damjanov, 1892-1958 was a hero of socialistic work. In 1992 the name of the factory was changed to han Krum (han=king). Thanks to www.9h1pi.com for info.

Damianov telegraph key