Classical Dutch oak lectern model with a
compartment witha hinged
cover at the bottom of the
cabinet, where coils and other
supplies canbestowed away.
The tuning condensers are by Undy, LF transformers by
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
had a nameplate of the company "Die Haghe"
which does not belongthere. 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
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
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."
45 x 43.5 x 23 cm
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