Die Firma Elprom KB dürfte Radiogeräte für den Export nach Ungarn und in die DDR hergestellt haben. Beginn um 1963, Ende 1966?. Slabotokov zavod; - Schwachstromwerk Sofia: genannt in "Geschichte der Rundfunkindustrie der DDR" (Hein) Seite 195 und "Funkamateur" Heft 10 / 1967. Zumindest Lizenzbauten und Nachbauten von Graetz-Geräten (Deutschland). Known as manufacturer of TV sets as also Radios for export.

"Kliment Voroshilov" - low voltage factory in Sofia in composition of the Scientific Factory in manufacturing telecommunications equipment in Sofia. Created in 1949 by combining all low voltage enterprises in Sofia (Telephone, telegraph factory "Radioprom", "Rodno Radio," "Ring ", etc..). Built in 1949 with the help of the USSR. Originally produced radios, telephones, automatic telephone systems low frequency amplifiers, meters, analog meters (ampermeters, voltmeters). In time digested the production of electro medical equipment and television receivers (1953-57), VHF radiotelephone (1961-65), VHF radios and professional radio-electronic equipment (1966-70).

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Weak-current factory "Kliment Voroshilov" In 1949, on the outskirts of Sofia, in periphery of the district "Sugar Factory" on the corn fields and urban landfill it was created an impressive plant that has an important role in the history of industrialization and development of Bulgaria. As an artificial conglomerate, it was gathered together all the equipment, facilities, machinery and staff at all major weak-current enterprises in the capital - the former: TT factory (Telephone-Telegraph factory) („ТТ фабрика”), "Radioprom" („Радиопром”), "Native Radio” („Родно радио”), " Ring " („Ринг”) and others. In it, have been developed and manufactured: - Radio; - Low frequency amplifiers; - TVs; - Electric gramophones; - Transmitters; - HF and VHF radiostations; - Manual and automatic telephone exchanges; - Telephones; - Electrometers and other electrical measuring appliances; - X-ray equipment; - Medical equipment for physiotherapy; - Radio-relay equipment; - Sealing phone systems; - Radio components and units for the production of the listed nomenclature - resistors, potentiometers, capacitors, relays, magnets, speakers and more.