"الملف 3/30 تجهيزات الزورق البخاري" [و‎‎٤‎١] (٦١٤/٦٩)

Technical
Specification
CIRCUIT ARRANGEMENT.
The basic circuit of the " 556 " is an 8-valve super
heterodyne using two radio frequency stages followed
by a frequency changer, two intermediate frequency
stages, a combined A.V.C. detector and first audio
amplifier, noise limiter and an output valve. There
is also the rectifier and an electron beam tuning
indicator. All valves have International octal bases.
TUNING RANGE.
The receiver will tune continuously from 10 metres to
500 metres (30,000 Kc/s. to 600 Kc/s.) in five over
lapping bands. Coil changing is unnecessary, each range
being switched as required by a wave-band control on
the front panel. The range in use is shown by an in
dicator on the dial.
TUNING MECHANISM.
A single control tuning with special vernier indicator
enables easy adjustment and setting of the calibrated
scale. The tuning mechanism is an excellent piece of
equipment, beautifully made and permitting smooth and
rapid operation. It is free from backlash and is noiseless
mechanically and electrically. The gearing reduction
ratio is 140-1 and the effective scale length of the tuning
dial is 36 inches.
DIAL CALIBRATION.
Four of the five wave-bands are calibrated in megacycles
and the fifth in kilocycles. A subsidary pointer working
off the main tuning mechanism ensures accurate dial
setting and simplifies the logging of stations when
accurate tuning is necessary in a particularly congested
wave-band. The dial is of satin finish with black numbers
and is easy to follow without eyestrain.
INTERMEDIATE FREQUENCY STAGE.
The intermediate frequency is 450 kc/s., using
permeability-tuned transformers. Careful design and
construction has ensured that the I.F. stages maintain
their set frequency and eliminates any tendency to
drift, due to climatic changes.
SENSITIVITY.
Sensitivity is better than 2 microvolts input on the
high-frequency range for an output of 50 milliwatts.
Comparative results are obtained with aerials whose
characteristics differ widely.
SELECTIVITY.
30 db. down at 5 kc/s. off Resonance.
SIGNAL TO NOISE RATIO.
Great care has been taken to ensure that a really good
signal to noise ratio is maintained.
IMAGE RATIOS.
At 20 Mc/s. the image ratio is 35 db. down.
» 10 .. 50 „
» 5 60
.. 2 „ 75
RESPONSE.
Twin-matched loudspeakers of excellent accoustical
balance and high-tonal qualities are fitted internally.
Provision is made for an extension speaker to be
connected. The overall response has been adjusted
to cover audio frequencies required for a good standard
of speech and music, and to attenuate those frequencies
which tend to bring in noise.
• CONSTRUCTION AND FINISH.
The panel assembly, chassis and components are fully
tropicalised. No cardboard-cased condensers are used.
All paper di-electric and electrolytic condensers are
fitted in specially sealed metal cases for additional pro
tection. The die-cast panel and chassis assembly ensures
extreme rigidity of construction which enhances stability
and is an important feature in a set that will be shipped
abroad and travel long distances over bad roads in
tropical countries. The whole assembly cannot warp or
rot and is fully insect proof. Protruding metal handles
afford protection to the receiver panel and controls
during packing and transit. The Receiver is pleasingly
finished in battleship grey and has an attractive blue front
panel. All fittings are chromium plated and the complete
set presents a neat, workmanlike and unobtrusive
appearance.
• GRAMOPHONE PICK-UP ATTACHMENT.
At the rear of the receiver connections are provided to
allow the use of a gramophone pick-up and the audio
amplifier stages give excellent musical reproduction.
• OUTPUT. The audio frequency output of the Receiver
is at least 3,000 milli-watts.
• EXTENSION SPEAKER OUTPUT.
This is arranged to match into an external extension
speaker with an impedance of 2.5 ohms.
• ACCESSIBILITY.
The panel and chassis are easily withdrawn from the
cabinet by removing 4 fixing screws. The Receiver
assembly is then accessible for inspection and servicing.
• I NPUT IMPEDANCE at Aerial Terminal 400 ohms.
• DIAL ILLUMI NATION. The dial scale is illuminated
by three 6-volt 1.8 watt, lamps with bayonet fitting. The
indirect lighting on the satin-finished scale gives adequate
illumination without glare.
• DIMENSIONS. Overall Width, 16,' inches ;
Depth, 10{ inches ; Height, 9 inches.
• WEIGHT. Unpacked : 40 lbs.
• PACKING.
The Receiver is initially packed in a stout well-designed
cardboard carton and then outer-packed for rail or
shipment in a standard timber crate. Every care is taken
to see that the possibility of damage in transit is reduced
to an absolute minimum.
• POWER SUPPLIES.
Four Models of this Receiver are available.
Cat. No. 556/A.C. for 110 volt and 200/240 volt, 40/60
cycles A.C. input.
Cat. No. 556/B. for 6 volt accumulator input
Cat. No. 556/D.C.110 for 110 volt D.C. input.
Cat. No. 556/D.C.220 for 220 volt D.C. input.
Models 556/D.C.110 and 556/D.C.220 use a standard A.C.
Receiver operated from a rotary converter which trans
forms D.C. to A.C. Separate converters are needed to
work from 110 volt or 220 volt D.C. input. It is import
ant, therefore, to state input voltage when ordering for
D.C. Mains.
• ACCESSORIES. Cat. No. 556/VAL : Set of spare valves.
Cat. No. 556/AER ; Set of aerial/earth equipment compris
ing wire, insulators, lead-in, pulley, halyard and earth tube.