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The N.V. Dordtsche Radio-Industrie was founded in 1928. The director was Mr. Wilhelm B. A. GŁnther, technical designer was M. Hellingman, teacher on a technical school and technician in Dordrecht. The company originated from a long-standing company of GŁnther, which traded in optical articles and medical instruments. The address was Groenmarkt 50 in Dordrecht. The factory made the 4-valve Dynaco A and the 5-valve Dynaco B receivers, a number of amplifiers and a radiogram, based on the Dynaco B radio.
The company did not exist very long. After 1929 no radios were made anymore.
Martinus Hellingman published the book "Radio telegrafie en telefonie; populair wetenschappelijke behandeling van de theoretische grondslagen, waarop een radio-zender en -ontvanger berust" ("Radio telegraphy and telephony; popular scientific description of the theoretical foundations on which a radio transmitter and receiver is based") in 1925. He also wrote a book on physics, was co-author of another book on physics and gave courses and lectures on radio technology at the Volksuniversiteit of Dordrecht. He lived at Reeweg 110 in Dordrecht.
In the October 1927 issue of Radio Nieuws magazine, he wrote an article about the electro-dynamic loudspeaker he applied a year later in the Dynaco radios.
In 1934 he made a short-wave transmitter for the MTS technical school where he worked. The station used the call sign PIIJ and transmitted at 42.35 meters. The transmitter focused among other things on contacts with MTS students in the Dutch East Indies. The station was still active in 1950.

This page was last edited on 14.07.2018