De Tijdgeest/Airvoice
    Type 4
Other items
For sale

4-Valve TRF receiver
Ebonite sloping control panel and oak cabinet. Classic lectern shaped model. The control panel was originally made of shining flamed black and brown ebonite. Exposure to sunlight gave the front plate an even brown colour.
The highly symmetrical control panel is divided into four rows. In the first row, binding posts for antenna and earth, situated on the upper left and right. In the second row we can see three coil holders. In the third row holds two rheostats. Left of the rheostats a switch that can be used to operate the radio on 3 or 4 valves; the on/off switch is situated on the right of the rheostats. The sockets on the left are for grid bias and filament voltage and the sockets on the left are for the plate voltages. Below the two switches, we see the knobs for primary and secondary tuning, the wave length switch and sockets for headphones and/or loudspeaker.
It is a secondary receiver with inductive coupling. A remarkable detail in this circuit is the fact that reaction takes place over two stages, a custom dating back to the time of bright emitters. Because of that, the right coil behaves in a different way: because of the extra phase shift, the point of maximum reaction lays further away from the central coil.
The first valve is a h.f. amplifier, the tuned antenna circuit is connected to the grid. The anode circuit is aperiodic. The second valve is the grid detector, coupled over two valves to the antenna coil. Valves 3 and 4 are used for l.f. amplification. Both stages use transformer coupling.
Filament current is provided by a lead accumulator; anode current by a 80 volts battery.
The original valve set is not known. Looking at the circuit, both LF tubes must have been the same.
The Airvoice Type 7 (shown above) resembles the Airvoice Type 4 receiver, but that radio has internal coils and variometer tuning.
 Data Valves  
Serial number: 358
Dimensions (hwd): 32,5 34 31,5 cm
Made in: 1925
Purchased in: 2011
Voltages: 4 /80 V

Click on a tube for more information


What was broadcast in 1925?


Listen to "Loca" by the Belgian-Dutch formation "The Excellos Five", Louis de Vries (tp), Henri van den Bossche (tb), Alphonse van Asbroek (cl, s), Joop de Leur (p), Bob Kierberg (dr, ld), recorded in Berlin, December 1925

The receiver was made with rectangular wire. Both transformers are by Transforma, Amsterdam. These transformers came on the market in March 1925. The capacitors are by Hart & Hegeman and the switches are by Utility. The grid leak resistor was made by Loewe. An a-periodic coil is visible on the left of the Transforma Super 1 transformer.
Advertisement in newspaper NRC, January 25th, 1925

Advertisement for Transforma Super LF transformers in Radio Expres, March 27th, 1925 The General Radio fine tuning knob and the radios type plate.

This page was last edited on 04.25.2019