HONG KONG DAILY PRESS, THURSDAY, JULY 2, 1931.
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FEATURES
HIGH POWER PICK-UPS.
THE INNER WORKINGS OF SOME TALKIES DESCRIBED.
Electrical reproduction of gramo There are various types of cine phone records, which is how be matographamopocze and ampli. coming so popular for home use, for units, phis rule theas em. roaches probably its highest dove ploy at least two turntables, so that lopment in the cinematograph when one rocord is finished it is not theatre where, of course, it is used necessary to interrupt the music in providing the synchronised whilst another record is subati sound for talking pictures (in cases tuted; the second record is already where disc-records are used), and rotating on the adjacent turntable also for the musical and instra (each turntable being provided with mental accompaniment effects to its own pick-up), and by means of otherwise "silent" pictures..........."
& control switch the completed re- In principle the electrical repro- duction used in the cinema is the same as that used at home, but at the same time there are, as you may, well imagine, many additional features, modifications and refine- ments necessary to suit the more serious and exacting conditions,
Enormous Volume.
cord is "faded out" whilst the second record is at the same time "faded in.?!!
Arrangement of Amplifers, The turntables, driving motors, pick-ups, amplifiers, switches and controls aro usually made up into a complete unit, which is encased in
MAKING MANSBRIDGE
CONDENSERS,
To judge from external appear- ances only, there is hardly a more thoroughly uninteresting
instru ment in the whole galaxy of radio gear than the average Mansbridge condenser.
It goes without saying that spark A small metal case of fairly Ing troubles must, therefore, be standardised pattern, two ter non-existent. Furthermore, it is minals or connecting tags growing from the top of it, and sometimes possible, by a suitable design, to a moulded base; that in all. Never- arrange for the armature to betheless, despite its far from thrill directly mounted, upon the turning appearance, the Mansbridge condenser embodies constructional table spindle so that it rotates at features of the greatest interest. turntable speed and in view of this very slow speed, mechanical vibration troubles are also virtually
eliminated.
Of course, the induction motor, although it can easily be made uni versal for voltage, can only he used on alternating current supply, and therefore is ruled out where the supply is D.C. ̧· '.
Watching for Distortion.
ule à milliammeter is As a rule à constantly in circuit with the am
& metal container both for mechani.plifier so as to indicate the anode cal protection and also for electri- current of the output stages, and also a careful watch on the needle serves as an instant indication of distortion due to overloading.
In the first place, the volume of reproduction which is required iscal shielding. enormously greater than anything In one well-known unit of this required in the home, and this fast kind transformer-coupling is used alone greatly increases the problems for the amplifier, transformers be involved in the design of, the aming arranged in parallel, with an plifers and the loudspeakers.
To obtain enormously amplified volume without appreciable "Ecratch
or "background." and also without any serious distortion, is by no means an easy matter, and calls for the highest skill and care in the design and construction of by the amplifiers and the loud speak
Cre..
output of about ten watts from four valves also arranged in parallel Additional power can also be ob tained if necessary by the addition of extra valves in parallel.
The Induction Motor...
The record turntables are driven
The high-tension current for the amplifying valves is often provided by means of a small motor-genera tor unit, the generator usually developing something between 600 and 1,000 volts D.C. If the mains supply is alternating current, the motor to drive this generator may also he of the induction type, which again helps to avoid any later
CAB motors, and in some ference troubles.
of the induction"
Accumulator LT.
these are type, whilst in other cases they are There are a number of gramo of the "universal type, employng
Of course, it is impossible to phone equipment available for a commutator. The universal typo adopt the same principle with the cinematograph purposes, and these of motor, as its name implies, can DC. generator, which must have a usually comprise a turntable ar bo used on either A.C. or D.C. sup-commutator in the usual way, but rangement with electrical pick-upply, and if it is wound for say, by making the commutator with a for playing the record and the 100 volts, it also becomes "univer-large number of segments the con- necessary amplifiers and controls, sal" for different voltages by the mutator, ripple becomes high-pit these being enclosed or mounted for simple process of including an ad-ched and is comparatively simple convenience in a metal container.justable resistance is series with to smooth out.
Non-Bynchronised Records, it. Where the record is synchronised with the film ita rotation must, of
Generally the filament current for The Universal Motor.
the amplifying valves is supplied The objection is sometimes raised by a heavy-duty low-tension accu course, be synchronously related to to the universal motor that spark-mulator-battery; in some cases this the movement of the projector, anding at the commutator enuses crack serves as a "bucer," and is actually ling in the loud speaker, but with on charge whilst it is in use, but usually the turntable is built up us
proper precautions this objection preferably the battery is discon part of the projector itself..
really amonate to verg. little. An-rected from charge whilst in use, other small point is that the ani- and a second battery is on charge versal motor generally runs at a ready to be instantly switched in in fairly high speed, and this is some times apt to give rise to a certain amount of mechanical vibration of
There is, however, a very large field for the entirely separate or non-synchronous turntable system, where the reproduction from the record, and the features projected upon the screen, although corres- ponding to one another in a general way, are not definitaly synchroni-
sed. In this case the definitely the synchronised. In this ense gramophone turntable unit hen-
the Procord..
Completely Isolated.
substitution if necessary. Usually. a third battery is also available na a standby in case anything should go wrong with either of the other two.
On the other hand, the induction The controls include the change motor has the undeniable advantage over switch mentioned above, the that the armature is completely main switch for connecting up the isolated electrically from the rest:
tirely separate from and not con of the motor; consequently there gramophono.motors and the supplyi
nected with the film projector, and may simply provide what is known ns "incidental" music or "eçects.".
RECORDING AND REPRODUCING.
no need for any commutator or any other type of electrical connection
to the armature."
to the amplifier, speed control for the motors and a volume control for the reproduction.
manufacture of Mansbridge densers
In this latter process the particles of tin which have been forced through the paper by the calender
ing rollers, and which, of course, if they were allowed to remain, would render the paper conductable on both sides, are actually burnt away.
The metallised paper is passed through rollers across which is con nected a highvoltage supply (about 2,000 volts), a bank of condensers being placed in parallel with the circuit.
Full of Holes. S
The result of this operation is
An ordinary fixed condensor, as you are aware, consists simply of alternate layers of tinfoil and waxed paper or mica. Now, one of that the particles of tin which pro- the disadvantages of this type of trude through the back of the paper condenser lies in the fact that it are burnt away, thus leaving a roll cannot be made in comparatively of metallised paper which is con large capneities without unduly in ductable on one side only, and creasing the bulk of the instrument, which is therefore suitable for Man-
Henes the inception of the Mansbridge construction. bridge, type of condenser, which was the invention, in 1900, of a Mr. G. F. Mansbridge, a Post Office en- gineer and which, up to very recent times, was manufactured under licence by four firms only,
|
If you happen to have bandy a piece of this metallisad paper taken from an old Mansbridge condenser, you can very reddily see the results of this electrical. burning process. Hold the paper up to a strong light and examine it through a powerful hand lens. The paper will be seen to be covered with innumerable, pin- holes, and to be quite different in appearance from an ordinary strip of tinfoil when examined under thu some conditions d
An Ingenious Scheme. The Mansbridge condenser de ponds for its functioning upon the use of "metallised" paper, & roll, of tough paper is taken and pure
Viewed under the microscope the metallic tin is deposited on it by means of a special process. In this effect is even more startling,. the state, however, the thin layer of entire body of the paper being seen metallic tin is hardly conductive to be riddled with gaping holes of enough for any electrical use. Theirregular"size" and pattern, roll of metallised paper, therefore, Strange us it may seem, the pre- | is subjected to a calendering opera. ¦ sence. of these pin-holes in the tion in which the paper it heavily metallised paper in no appreciable pressed between rollers moving at way affects the efficiency of the
material for use in condensers, different speeds.
The consequence of this treatment The paper is cut up into suitable is that the metallic particles are lengths for use in the construction more or less forced into the body of Mansbridge condensers Two- of the paper, and are brought into lengths of the metallised paper are one another. So great is the pres paper strips. The interleaved stripe permanent, electrical contact with taken, together with two plain
sure to which the paper is subjected are then rolled up together the that many of the metallic particles necessary condenser connecting nre forced right through to the tags, of course, being slipped in at:
talento į suitable places the roll" subjected other side of the roll-
Owing to this fact a further ope to high pressure, embedded in wax, ration is necessary before the metal and finally placed in the now fami- lised paper becomes suitable for the liar Mausbridge casing
HAVE YOU HEARD THESE? ›
Esṛe are «Ulits of long-wavD and short-wave stations which should be picked up by anyone in Hong Kong who has a mode rately good set suitable for re- calving such signals, Success in picking up these stations also": deponds very largely upon tav curable atmospheric conditions, Renders. ars, invited to add to this list should they succeed in picking up any station not in cluded in either of these lists,
LONG-WAVE STATIONS.
Wave length
Call Kilo- "Sign":"cycle
(Metres) Station
$60 Manila 977 Shanghai 345. Tokyo 353 Hiroshima 255 Hong Kong Z.B.W. 357.1 Bombay
361 Sapporo 366 Keijo, 370 Nagoya 370.4 Calcusta 380 Kumamoto 300 Sendai: 395 Dairen u 400 Osaka 410 Canton 480 Manila
SHORT-WAVE. STATIONS.
K.Z.L.B. 1,153 K.S.M.S. 1,083. J.O.A.K.870- J.O.F.E 650 848
V.U.B, 840
J.O.LE 830
· J.O.D.K. 820 J.O.C.E. 810 V.U.O 509.9 J.0.0.K. 790' J.O.HK 770 J.Q.A.K. 760 J.O.B.K. 760. C.M.B." 739
··K.Z.R.M.
Tixa (Hono Koxa)
OT: WORKING
4,484 Mon., Wed & Fri, 6 pm. 4 2 am
STATION
+ DÀI BIỂ
50,
67.65 Dobints (Germany) A.F.K.: 60,19 Khabarovsk (Russia). RAST. 56.7
Nautanw
A.G.J. Mosco
4,090 |6—30 pm,
6,201 Not regulár
RYN
435
Home
6,906
Perth
6.4.0.
418
Singapore
89.0
-87.
Kootwijk (Holland): Bangkok (Blam);
B6 Bydney?!
V9.1.4.B POLA HSAFJ 9.B.LA
8,108 Fuse & Fri.,
1,220 Not regular
- 31,55 | Melbourne a 31.48 Bekenectady
4,000 | Tary Thurs, Sat., & pan,
Bunday midnight
7,148 Daily 8.80 p.z. & 11 p.m.
7,310 Not regular..
4,780| Daily 11. p.m.
0,503 Not regular
*W.LIAE. 0,580 Dally 7 aim, 1
It is impossible to keep the are amplified. When the pulses,. much magnided, arrive at the am-needle of a milliammeter in tho plifier output, they are fod into plate of an ordinary power valve Quite an interesting way of conwhat is really a glorifed pick-up still if a lower voltage is employed 42 sidering the electrical recording of
are out down so that (unless working backwards. gramophone records is to look at
they are too weak to be useful), Instead of the needle. movement But it is quite surprising what it as just a reversal of the process causing current to-flow in the wind good results can be obtained with a to many of us employ to play our 15
e-rolt pentodo valve of the ordinary ing as in the case of a pick-up, all type.
31.20 Pindhoven (Holland) P.C. | recorde electrically.
currents Bowing through the wind-
81.28 Sydney skuskan bay Bmall H.T. Battery Buitable, Fundamentally, the apparatus
ings from the amplifier cause the As a rule all pentode valves are 24.5 Bydasy used is very similar, although, of neodle to move. This neadle, or looked upon as requiring much course, the power employed in the stylus, as it is called, is arranged H.T. current and usually high H.T. recording amplifiers is much great so that it traces a wavy line on a voltages In spite of this it is pos or. Instead of a loud speaker which ost record which is afterwordsible with a small pentode valve to 24. Bohenectady
pecially treated and used to proget ordinary room loud speaker
18.89 Ban gives out sound by changing electris vido moulds for making the ordin strength with only 60 volts H.T
....164. Hootwijk (Holland) currents into sound waves, a micro-ary records,
and that without any appreciable 17 Handon kicking of the, milliammeter noodig, 18.9 Bangkok phone is used to take in sound
The connections to employ are: 18.4 Kootwijk (Holland by changing sound waves into elec
14.74 Bandoang those normally employed with a tric currents,
pentode valve, the extra terminal 10.6 Nanoy (France)
18.15 Pittsburg de
# Pick-up * Working Backwarda. Having thus obtained our very ing electric currents, they are, an- pliled by the valves just as the varying pulses from our pick-ups
LOUD SPEAKING ON 50
VOLTS H.TV
0,020 Fri, 8 mm, Sat, 8'am. § 10 ám. 9,590 Not regule
0,677 Midnight daily
11,020
sight-8 m. daily
7.30 p.m. & ♬ am, daily, szorpt
12,240 Nightly
2.F.C.
27.8
Kalola (Konya)
Bandoong
7.10.
10,526
Not regular
25.08
PLE Chalmedord (England) 8.8,W,-
11,7517.30
K.LX.E.
W210
PLG. POT ELF |HLS.1PJ
PAK PLE
28,85
It is usually taken for granted being taken direct to the 00-volt that formandistorted, loud speaker | tape. Dus to the lower E.T. zoltage, mas um results, oven at all rooms than usual the current consumed strength, it is necessary to have nt is much less, with the result that the very least, 100 volts H/T. In the valve boogmes in promosition the normal way this is, of course, | quite suitable for a moderate capa. quite true,
city dry H.T. battery,"
Baturday and Sunday
128604 Wed, Fel, Bat
16,102 Dally 6.10 p.m. to midnight 10,804 Dally 7 P
1722801 Daily&p..
midnight.
17,761 Sundays 7 p.m. de mild 10,604 | Each afternoon 2 19.220 Daily 30-7 pm.
ZA, ON 310,851. Daly Sam. W6.XK 1,542 Not regular
fAllowance mutf be made for at adrimes Dean onuntries, which is one hose abend