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.
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.
company did not exist very long.
After 1929 no radios were made anymore.
Martinus Hellingman published the
behandeling van de
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.