The radio section is a high sensitivity superheterodyne ,
using a larpe diameter loopstick aerial for increased signal
pickup and incorporating two I.F . amplifiers 1'nr high
Drift transistors áre used throughout for high gain and s
tab ility .
The loop3ticl: winding is matched to the se lf oscillating
mixer for optimum signal to noise ratio and the I.F . signal
to the I.F . amplifier by means of a bottom capacitively coupled
bandpass circuit consisting of L3, L4 and the coupling capacitor
C8. The base circuit of both I.F . amplifiers is matched to the
I.F . coils by means of a capacitive tap to ensure high transfer
efficiency. The diode detector D2 is arranged to give positive
output voltage, and A.V.C. io applied to the f ir s t I.F .
and to the converter via the damping diode Dl. The f i r s t
amplifier also acts as D.C. amplifier for the damping diode and
enables the audio output to be held constant over widely varying
A high resistance volume control is connected across the
diode load R14 to make low listening levels possible and to give
the correct volume control law. A bass boost network, consisting
of R16 and C21, is connected to the tap on the volume control to
give loudness compensation at low volumes.
The 8'jdio preamplifier and driver are a D.C. coupled pair,
with D.C. feed-back applied by means of R18, R22 and R21, giving
good thermal stab ility . The output stage is connected in
push pull, so that the output transformer may be omitted, thus
eliminating any power loss and giving greater battery
well as extending the frequency range. The transistors are
adjusted for B class operation and quiescent current is set
base divider networks. Each transistor has an unbypassed emitter
resistor to equalise their characteristics and they are
compensated by the N.T.C. resistors R27, R28, and the shunt
resistors R25, R26. Negative feedback is also applied via the
bias resistors R29, R30 and by C26, G27, allowing the output
to run with very low distortion. To further reduce the
and to minimise gain variations, negative feedback is applied
overall by R24 and the unbypassed emitter resistor R20.
Because of the large D.C. feedback and thermal compensation
the receiver may be run at temperatures as high as 120° F.