Specifications

CONSTRUCTION
with the help of potmeter VR1 (audio
B/W control) by changing the voltage at
pin 2 (phase comparator section) of IC.
Potmeter VR1 generally changes the
phase of the audio signal.
After processing of the audio IF sig-
nal, including its amplification and recti-
fication, an AF output is available at pin
14. The audio output is further amplified
by transistor amplifiers built around tran-
sistors T1 and T2 (2SC2458), which de-
velop 1-volt peak-to-peak audio output
across resistor R16.
Potmeter VR3 acts as an audio gain
control.
Video section: This is divided into four
stages, namely, video amplifier, video de-
tector, video driver, and video-output
stage.
Signal from baseband output of tuner
module is fed via resistor
R17 (2.2 kilo-ohm) to the
base of video amplifier com-
prising transistor T3
(2SC2458). Capacitor C17
and resistor R19 are used to
suppress the interference.
R20 (1k) is used for emitter
bias.
Video signal is taken
from the emitter of transis-
tor T3 and fed to video de-
tector IC2 (NE592) through
an LC network comprising
capacitors C18 through C20
and inductor L4 (a video
take-off coil). Pin 1 of IC is
taken as reference input and
pin 14 is taken as signal in-
put. A suitable positive bias
is given to pin 1 and pin 14
through resistors R22 to R24.
The output is taken from
pin 8 of IC (positive video)
and fed to the video driver
as well as the output stage
comprising transistors T4
and T5. After amplification
of video signal, 1V peak-to-
peak video output is taken
from the emitter of transis-
tor T5 through capacitor C25
and resistor R29. Potmeter
VR4 (4.7k) is a video gain
control, which is used to ad-
just the contrast of picture.
Signal-strength indica-
tor. To indicate the signal
strength of the incoming sig-
nal, a 250µA ammeter (or
VU meter used in stereo
decks) is employed. To drive
the meter, an amplifier com-
prising transistor T6
(2SC2458) is used. The sig-
nal from baseband output of
tuner module is fed to the
base of transistor T6
through resistor R18 and ca-
pacitor C26. Positive bias is
given to the base of transistor through
resistor R30 (47k). The high-frequency AC
output is taken from the collector of tran-
sistor T6 through capacitor C28 and fed
to the voltage doubler circuit comprising
diodes D3 and D4 and capacitors C28
and C29. The output is fed to
microammeter via potmeter VR5, which
can be adjusted for convenient deflection.
A double-sided PCB has been used,
Fig. 6: PCB layout for the circuits in Figs 4 and 5 (track-side)
107