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 The control panel was originally made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.
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
Inside
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.
Front
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.
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