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Two-circuit Koomans TRF receiver
Classical Dutch oak lectern model with a compartment with a hinged cover at the bottom of the cabinet, where coils and other supplies can be stowed away. The tuning condensers are by Undy, LF transformers by Lissen.
Above left, the antenna connection, the four valves and the earth socket, below that, a series/parallel switch, four rheostats for the filament current of each valve and an on/off switch. Below the rheostats are the three tuning coils, and on the right, connection points for the different voltages. Entirely underneath are the knobs (with fine tuning) for primary and secondary tuning and the terminal sockets for headphones and loudspeaker.
The radio had a nameplate of the company "Die Haghe" which does not belong there. It was transferred from a 1930 "DH" AC receiver on this device.
Nicolaas Koomans (Delft, December 18, 1879 - The Hague, October 4, 1945) was Chief Engineer of the Telegraph and Telephone Agency and Chief of the Radio Laboratory of the State Telegraph Agency. He was one of the first radio amateurs. In 1916 he was one of the founders of the Dutch Association for Radio Telegraphy (NVVR), and became member of the board. In the following years he held numerous lectures and demonstrations for this association and has published many articles in its organ "Radio Nieuws". He also designed a "simple" schematic for building a three-valve amateur radio receiver, which became known as the "Koomans circuit". A large portion of the early Dutch amateur receivers is based on this design, which later was expanded to a four-valve design. An article, written in 1926, describes this design: "In this schematic, both the grid circuit and the  H.F. plate circuit were tuned with the aid of tuning capacitors, causing an increased tendency to generate spontaneously.
A main requirement with this kind of receiver with RF amplification, is to keep the primary coil completely outside the coupling area, flat against the front plate, and to make the wire connections to the coil holders so that a counter-acting coupling is created, as soon as one slightly couples the primary coil with the secondary coil.
By doing so,
one can counteract the tendency to generate, without loss of volume."

Nicolaas Koomans

Data Valves   Circuit  
Serial number None
Dimensions (hwd) 45 x 43.5 x 23 cm
Made in 1926
Purchased in 2017
Click on a valve for more information Click on the circuit to enlarge

What was broadcast in 1925?


Listen to "Always" door George Olsen & His Music, sung by Fran Frey, Bob Rice and Edward Joyce, recorded in 1926

A look inside

This page was last edited on 04.07.2019