Otto S. Knudsen, Radioapparater og Materiell en gros, Trondheim (1942)

Radiofabrikk Stentor A.S., Fjordgt. 25, Trondheim (1946)
Stentor Radiofabrikk A/S, Trondheim (1968)

A/S Stentor Alvdal (1969), subsidiary of Stentor Trondheim, Stentofon speakerphones.

Stentofon began life in 1946 as Stentor Radiofabrikk, specializing in radio communication systems for ships and for fishing boats. Stentor later extended its range with intercom systems that it sold under the brand name Stentofon.

Stentofon remains an international brand today, busy in the communcation industry. Stentofon is as of 2014 part of the international Zenitel group.

In Radiohandleren Nr. 2, Februar 1946, Otto S. Knudsen published the following notice:

"From April 1st this year, the production department and workshop of my company are separated and continue under a new name: Radiofabrikken Stentor A.s.
The administration is the same for both enterprises and the construction program remains unchanged."

While Radiofabrikken Stentor was therefore formally founded in 1946, there must have been prior activity (including production).

Stentor's production output in 1968 amounted to 7.8 million NOK (norwegian crowns). In January of the next year, the factory in Alvdal was founded. That same year they produced 150 speakerphone sets daily under the Stentofon brand, with a production output of 4 million NOK.