battery operated portable receiver
medium wave reception.
Wooden casing, painted black. The sides are covered with
black book muslin. This muslin also covers the frame
antenna wrapped around the sides. The top and the knobs
of the radio are made of bakelite. The radio can be opened by turning the screw in
the middle of the front panel. The price was 210 Kč in 1935.
circuit of the Weekend is based on an invention by E.H.
Armstrong from 1922: the super-regenerative
receiver. This principle can be used to make a
sensitive receiver with a minimal amount of
components. A detector with feedback (in this case a
A441N, set-up as Negadyne) oscillates in a normal way,
but this oscillation is periodically interrupted by
a much lower frequency,
the quench frequency. This frequency must be just
above the audible frequency. As a result, impulse modulation in
the anode circuit of the valve is created, in the
rhythm of the modulation of the transmitter
Advantages are high
sensibility and a simple circuit. Disadvantage is
the whimsicality of the circuit, specially in low
frequencies like medium and long wave.
The extra coil with
the 1500 cm capacitor (see circuit) were added to
make the circuit oscillate in the quench frequency. (With
many thanks to John Hupse)
Listen to "Hola
sung by Kamila Strnadová and Oldřich Kovář,
recorded in 1935
On top, two knobs are visible: on the
left a rheostat and on the right, tuning. The A441N is
mounted in a horizontal position; behind the tube a
small mounting board with components can be seen. The
thin wire that comes from the variable condenser (top
right) and disappears into the wooden panel, leads to a
frame antenna inserted between book muslin and the
wooden sides and bottom. The battery compartment houses
six 4,5 volts batteries (see pictures below).
Vladimír Fiala from the
Czech Republic mailed me a scan of the wrapper
of a Telegrafia battery
right, rheostat. Between the knobs a number of
sockets. Top and bottom, across, two
connections for headphones. The middle socket can be
used for an aerial.