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Four valve battery radio made in 1926

1927 model

1928 model

Because the receiver was made between 1926 and 1928, it underwent some changes. The first model had lamps on the top and coils at the front, in a later model (picture left) the tubes are fitted internally and the coils are still at the front. Photo 2 shows a slightly larger 1927 model, with internal tubes and internal feedback. The third device has a flap on the front and top. Strength control is somewhat simplified, the knobs are symmetrically distributed over the front and the tumbler switch in this model is now a push/pull switch. All radioss work with resistance amplification. The tube layout is unknown but probably will have looked like this: HF: A409, detector: A409/A415, LF1: A425, LF2: B406. The receivers from 1927 and 1928 have an extra antenna socket and a connection for headphones. The long wave with these radios is divided into 2 parts: 800-2300 and 2300-3200 meters. The medium wave range is 200-800 meters.
The radios are not only beautiful to look at, the chassis are also very well designed.
The radio was advertised in leaflets and advertisements as: "built in The Netherlands by Delft engineers". It was most likely made by Radio-Technisch Bureau "Broadcast", Sonoystraat 75 in The Hague. The owner of this company was H.G.A. Rundervoort.
In any case, Delft engineer L.H.M. Huydts (also working at Waldorp) contributed to the receiver: he designed "strength control". The antenna coil in the Koomans circuit is tapped into 8 taps for course tuning to the wavelength. A variable capacitor is connected in parallel to this coil, which uses the same taps. These taps are also used to couple the detector grid to a smaller or larger part to the coil. The advantage of this circuit is that with this special grid connection one can suppress the RF generation tendencies, control selectivity and the circuit can serve as a gain control. The circuit (see opposite) was previously discussed in a slightly modified form in magazine Radio-Nieuws. Coils I and II need not be inductively coupled. Coils I and II, together in series, form the antenna circuit with the parallel capacitor. By making coil II smaller, gain is reduced.
Resistance amplification used in these radios was also attributed to ir Huydts in advertisements, but that principle had been known for much longer. Ir Huydts regularly lectured in the country, demonstrating Crystalphone radios. He tried to prove that resistance coupling sounded better than transformer coupling by having two devices play behind a curtain and let the audience decide, but that was not successful in all cases.
It was recommended to use a Farrand Senior or Junior loudspeaker or a Sandar double cone loudspeaker.
The radios were sold at the Kunstzaal Edison in The Hague or at a number of agents, e.g. in Amsterdam, Rotterdam and Utrecht.
The original price was f 265,-. The price of a Farrand Senior loudspeaker was f 55,-. The 4A was last sold in 1928; in late 1928 the AC receiver 3W was introduced.
Data Buizen
Serial numbers: 1190 (1926), 1247 (1927), 1543 (1928)
Dimensions (whd): 38.5 38.5 25 cm (1926)
44    42  27 cm (1927)
45  x 43.5 x 33.5 cm (1928)
Made in: 1926 / 1927 / 1928
Purchased in: 2007 / 2018 / 2021
Click on a valve for more information

Circuit 1926

What was broadcast in 1926?


Listen to "Why Don't You Say So" by the orchestra of Jack Hylton, recorded on January 25, 1926

Back of the 1926 model Back of the 1927 model Back of the 1928 model
In the compartment under the chassis, a coil set and a battery for negative grid bias (-4,5V and a tap for -1,5V) can be stored. Jacks for other voltages, a loudspeaker, earth and antenna and two rheostats are situated on the back of the chassis. Terminals for the LT and HT voltages, the loudspeaker, earth and antenna and two filament rheostats are located on the bottom plate of the chassis. They can be reached via the top cover. The negative grid voltage is made by a resistor in combination with a capacitor. The layout is the same as that of the 1927 receiver.

Top view of the 1926 model

Top view of the 1927 model

Top view of the 1928 model

  Terminals for the LT and HT voltages, the loudspeaker, earth and antenna and two filament rheostats are located on the bottom plate of the chassis. A black painted brass cap (removed here) covers the tubes.  

Under-chassis view (1926)

Under-chassis view (1927)

Under-chassis view (1928)

Type 4A with valves on top; early version, 1926

Advertisement in NRC, November 1st, 1926, early version

1927 Model with internal tubes and internal reaction contro. In the background a Farrand loudspeaker

The Farrand Senior loudspeaker

Advertisement for the 1927 version of the 4A in Radio Wereld, November 10, 1927

Advertisement in NRC, October 27, 1927

This page was last edited on 15.05.2021