Murphy B831 Service Instructions Manual

SERVICE
INSTRUCTIONS
Murphy
MODEL B83|
PORTABLE
RADIO
4558
SPECIFICATION
GENERAL
Model B831 is a battery operated portable receiver with
coverage of the Long, Medium and V.H.F. wavebands.
The receiver has an additional range which provides
electrical bandspread of the high frequency end of the
Medium waveband.
The receiver incorporates ten transistors and three
crystal diodes, an internal ferrite rod aerial for the Long,
Medium and Bandspread ranges and a telescopic rod aerial
for the V.H.F. waveband. A socket enabling the receiver to
be used with a car aerial is also fitted, being operative on the
a.m. wavebands only when dispatched from the factory.
The car aerial socket may be used on the f.m. band instead
of the a.m. bands after suitable modification.
PRESENTATION
The receiver has a four-piece moulded cabinet with front
rear and sides covered with dark grey/blue material. The
side trims are finished in sprayed silver whilst the loud-
speaker grille and the small grille at the rear of the cabinet
are of moulded plastic. Combined with the scale is a satin
finished silver strip beneath whichis mounted the five button
switch unit. To the right of the press buttons are the three
edge operated controls moulded in off-white. The cabinet is
fitted with a full width carrying handle in polished alumin-
ium. The detachable moulded base is secured by two quick
release catches and affords access to the batteries which
are retained to the moulding by two straps. Projecting
through the scale in the top left-hand corner of the receiver
is the telescopic rod aerial. The car aerial socket is located
on the left-hand side of the cabinet. A socket for use
with an earpiece is mounted at the rear of the cabinet on
the left-hand edge of the top moulding.
CABINET DIMENSIONS
Height: 7% in. (18-7 cm)
Width: 124 in, (31-8 cm)
Depth: 41 in. (10-8 cm)
The above dimensions include projections. The total
height with the carrying handle erected is 8] in. (22-5 cm)
Weight: 4 lb 15 oz (2:2 kg)
CONTROLS
Top left: Five press buttons selecting—Off; Band-
spread; L.W.; M.W.; V.H.F.
Top right: Volume; Tone; Tuning.
WAVEBANDS ;
L.W. band—1,070-1,900 metres (280 to.158 kc/s)
M.W. band—185-570 metres (1,625 to 525 kc/s)
B.S. band—185-210 metres (1,625 to 1,425 kc/s)
F.M. band—87-5-100 Mc/s (3-4 to 3 metres)
AERIALS
An internal ferrite rod aerial is fitted serving the three
a.m. ranges. A telescopic rod aerial is fitted for use on the
f.m, band. Additionally, a car type aerial socket is provided
which is operative on the a.m. bands only as supplied.
The receiver may be modified so that the aerial socket is
Operative on the f.m. band instead of the a.m. bands. No
aerial changeover switch is fitted.
AUTOMATIC GAIN CONTROL
Two controlled stages on a.m. only.
INTERMEDIATE FREQUENCIES
A.M, 470 kc/s, oscillator high with respect to signal.
F.M. 10-7 Mc/s, oscillator low with respect to signal.
BATTERIES
Two Ever Ready PP9 batteries provide the operating
voltage of 18 volts. The battery consumption is 19 mA on
the a.m. bands.and 21 mA on f.m. .
AUDIO OUTPUT
1 watt.
LOUDSPEAKER
8 in. X 5 in. (20-3 X 12-7 cm) elliptical. Flux density 8,000
lines per square centimetre. Impedance 25 ohms.
TRANSISTORS
VT1 AF178 r.f. amplifier f.m.
VT2 AF115 mixer f.m.
VT3 AF117 oscillator a.m.
VT4 AF116 mixer a.m., if. amplifier f.m.
VT5 AF116 Lf. amplifier
VT6 AF116 if. amplifier
VT7 AC127 = audio amplifier
VT8 OC81 driver
VT9 AC127 output stage
VT10 OC81 (complimentary pair)
CRYSTAL DIODES
Multard type
D1 OAT79
De OAT79 f.m. detector
D3 OA9Q0 a.m. detector
PHONE SOCKET
A socket is provided at the rear of the top moulding into
which may be plugged an earpiece having an impedance
of not less than 50 ohms. Alternatively, this socket may be
used with an external loudspeaker of 25 ohms impedance,
or for tape recording.