MUSIC FROM MANY COUNTRIES
by wireless with
TELEFUNKEN 40
Long range All-Electric receiver with ' „atation, selector for use with batteries or lighting maine....
with TELEFUNKEN
LOUDSPEAKER
ARCOPHON
HONG KONG DAILY PRESS, THURSDAY, FEBRUARY 19, 1931.
TADIO
For Demonstration and further particulars apply to: SIEMENS CHINA CO.
TELE FUN KEN
Office-Pedder Building, 4th Floor. Showroom-27, Nathan Road, Kowloon,
Canton Office-Shameen.
Swatow
-Gebr. Roese.
TELEFUNKEN
LONGEST EXPERIENCE-LATEST DESIGN.
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Ask Us For Demonstration
THE SINCERE Co., LTD.
DISTRIBUTORS.
FEATURES
MORE PRACTICAL HINTS.
CONTROL OF HIGH-FREQUENCY.
CAREFUL MATCHING OF CONDENSERS.
chokes and so on ought not to be fitted anyhow, but tests should be made to discover whether lossc. are boing introduced.
SOME USEFUL TIPS. One of the best methods of check ing distortion is a milliammeter connected in the plate lead of the last valve.
Condensers of the non-inductive series with the capacity of the valve type are now readily to be obtain produces the euiting down effect described. At the same time, the ed. These components offer low effective capacity across the tuned impedances to rádio-frequency purcirouit is reduced and so is 'tho rents and are, therefore, of great amount of the feed back. This last value in high-frequency circuits for haviour of the rest of the set may effect is important, as the be
by-passing and other purposes.
What you must not overlook, however, is that Jong wires offer considerable impedance to high frequency currents. It is therefore necessary to use short connecting wires, in order to obtain the maxi-screens. The capacity may well bhias to the power valve is too high,
mum benefit from the particularly good condensers.
be affected.
E.F. Choke Details,
characteristics of a high-frequency It is generally realised that the choking coil may be greatly affect ed by mounting it very near metal
wavelength of the choke. altered and therefore the natural
If your last valve's ruilliammeter kicks upward to a higher reading when loud signals are received, it indicates that the negative grid
low.
*
Downward kicks of a millinm- Its inductance, too, maỷ bỏ TE- This cannot always be arranged. duced, and this will affect the chok-circuit indicate that the distortion moter in the power valve's plate Some condensera aro so shaped ing action. Care should, therefore, is due to the grid bins being too that wires several inches long are be taken that the effectiveness of necessary. Perhaps some day won choke. is not impaired by placing shall have condenser with terminals | it in, nʼset where its characteristics where we often want them, that is, are altered... near the bottom, instead of at the top of a moulded case.
Careful Matching.
We usually rely upon the manu facturers to provide a correctly matched tuning condenser, but it is not always wise to accept the component without testing it. Per.. haps I should say that the conden sers are usually very good, "but when the tuning of the set seems rather dess selective than expected and when we know the coils are satisfactory, it is then time to look into the matter of the
nepes each coil capacity
Do not overlook the fact that chokes have external fields and that a pair of chokes used near together in a set may be so strongly counled, that the results are gravely affect ed. Instability and loss of magni- fication may often be traced to this nearness of the chokes.
Metal Chassis
Aluminum chassis are being ex tensively used in good-class wire- less acts just now, Naturally, some at least of the parts used have to he specially arranged in order to cunt & petal to remember all the
metal base plate. We have cireuit capacities as well time is that the chassis is a con as the condensers themselves and ductor, usually earthed, Thus we will hssume that at one fre capacity effects are possible All quency the tuning condensers haywires passing near the chassis form, been adjusted to put the circuits with it little condensars. into tune. If now we find, that at Sometimes, a grid wire of some a different, frequency the circuits length is left. Losses are then aru, no longer accurately in tune, bound to Decur. In other parte. of we may expect to find the gang the circuit, we may also introduce losses by the placing of the parts themselves, Fixod condensers,
condenser inaccurate. so t
It is difficult to correct a tuning condenser, as you will discover if you try and I advise that the com- pozent he left alone and be return led to the nrakers. Sometimes a set of moving plates will be bent by accident; inspection may show an obvious fault.. It is not wind to start bending platen, for you will And that ha soon as the thing ás put right in one position, it is put out in another.
Screening-off Valves.
I see that some designers fit a screen having a hole in it through which the screen-grid valve possce, while others do not bother with this, but cover the valve as a whole. or leave it standing without shield- ing it at all.
When the coin and condensera are completely shielded, there may scem no great advantage in also shielding the scron-grid valve. But actually, unless the valves in the set are woll spaced, the 'etabi- lity in increased by covering the screen-grid valve and sometimes the detector as well,.
A fairly strong coupling may exist between valves if they are close together. This is avoided by shielding. In sets having · more than one high-frequency shielding carefully cannot be over locked..
Control of H.F.
stage
Increasing the H.T. on a power valve, and increasing grid bins: to correspond with it, enables the valve: to handle a larger output, and thus eliminates distortion due to slight over-loading,
*
cramped, and you have difficulty in If your panel space is rather
fitting a panel bracket, remember that triangular pieces of wood-ean be very satisfactory in place of metal brackets.
The loss of emission after a valvo has seen long service is often first indicated by failure to get the usual reaction effects,
Although a twisted connection in the aerial or earth lead will give apparently satisfactory reception. for a time, it is certain to deterior nie rapidly and cause heavy loss of strength after a few weeks.
The capacity of a good variable condenser when all out" is not
more than about one-tenth of its maximum capacity when all in."
HAVE YOU HEARD THESE?,
Here are lists of long-wave and short-wave stations which. should be picked up by anyone
in Hong Kong who has a mode rately good set suitable for re- -colving such ́signals. Success in pleking up these stations also depends very largely upon fav 'dorable atmospheric conditions. Rondors are invited to add to this list should they succeed in picking up any station not in. cluded in either of these "ilato,
LONG-WAVE STATIONS;
Πάνο length
Call Kilo. (Metres) Station Sige cycle 200. Manila .K.2.1.2. 1,153 977 Shanghei 5.5.M.8. 1,035 280 Ticntain C.R.: 1,070 310 Shanghai - K.R.C. 967 320 Peping
C.O.P.K945 345 Tokyo J.0.A.K. 870 333 Hiroshima 1.0.F.K. 550 333 Hong Kong Z.B.W. 846 357 Bombay.. V.U.B. 840 361 Sapporo J.0.1.K 360 Keijo J.O.D.K. 820 370 Nagoya
J.0.0.K, вта 370.4 Calcutta V.U.O 809.0
380 Kumamoto J.O.G.K. 700
300 Bendai
365 Dairen
308 Rangoon .V:U.R. S -400. Onaka
.:
J.O.H.K.
770-;
J.D.A.K.
740
754
J.O.B.K
780
KZ.R.M 798
410 Canton C.M.B. 413 Manila
SHORT-WAVE STATIONS.
STATION
CALL BIOM
The potentiometer method of 67.85. Dobintz.(Gocmany) A.F.I. controlling the amount of the high--60.13 Khabarovsk (Bussia) B.A.07.
36.7 Nauen- frequency signal applied to the
first valve in the set is satisfactory 29.6
up to a point. Given a good poten tiometer, o fairly smooth variation | 413
- BO.. Moscow
Rorie Perth Bingapore
is obtained. 59,9 || Kootwijk (Hallod) The fact is, that owing to the 37 Bangkok (diam)". capacity of the valve, to which the 188
39:4 Sydney
81.68 | Melbourne
potentiomoter is connected, wo do 31.48 Behenectady not obtain true potentiometer 81.20 Eindhoven (Holland). action. Thus, if the arm is act 81.28. Sydney three-quarters of the way towards 81. Nairobi (Kanya)
BŠAPJ
Kno
CTCLES
Trus (Hoso KONG)
er. Working
4434 Men, Wed & Fri., 6.p....2... 4,090 6-10 p.m. -
·6,201 | · Not regular
8,000 6, Thurs, Sat., 8 p.m.
6.816 Sunday midnight
7.143 Dally 6.80 p, 4-11 p.m.:
7,820 Not regular"...
7,730 "Daily, 11 p..
8,108 Tuos, & Fri, 9 pm.—1 am.
9,230 Not regalar
| 91,603 | Not regular
Sat, 8 am, & 10 am.
AC-SG3 Set
ENTIRELY MAINS OPERATED
A sentation in 3 valve sets, with 1 watt undistorted output; enough power for any moving coil or dynamic loudspeaker. A set that will appeal to you whether you are interested in perfect quality from the local station or clear reception from distust stations.
Price only $145.00
Including Mazda Valves (the best British Valvee).
domestio
Special B ELIMINATOR for any set or made to order for any requirements.
For
perfect reception
use
MAZDA" Valves,
large stock newly arrived
RADIO batteries made by new process minimis- ing deterioration "TERTRIX" 150, 100, 60, 45 volts and C. batteries.
Ebonite "TROLIT" and Pressed Fibre Panels cut in any size. Loudspeakers, and various parts are also obtainabl",
For further information apply to:-
CANTON TRADING ASSOCIATION, LTD.
CHINA BUILDING (5TH FLOOR).
TELEPHONE 24610.
EVERYTHING (SE.C.) ELECTRICAL
FOR THE HOME WITH ELECTRICITY
HOUSEHOLD
"Magnet"
An
AGJ.
B.EN.
IMA
Q.A.G..
V.8.1.A.D.
P.Q:L
2.B.I.. 3.1.0.
W.2.1.A.F.
2,530 Daily 7 am
P.C.J.
0,020 FTL 8
2.F.C.
9,500 Not regular
7.1.0.
9,677 Midnight daily
Sydney 27.8 Bandoong
2.M.E.
10,528 Not regalar
PLE
11A120 Midnight-a m. daly 11,761 7.80 p.m. & Aa.m. dally, except
Saturday and Sunday
-245
Manila
38.85 Bohonestady
Bandoeng
18.4 Kootwijk (Holland). 174
24.0 18.3*
5.1.X.E W.2.X.0. F.L.G P.C.L P.LY Bangkok
H.8.1PJ POK Kootwijk (Holland) 15.74 Bandoeng
12.240 Nightly
Irons Kettles Toasten
12,850 44.12.
Wed., Fri., Bat.
PLEA
the full on position, we do not 286
apply three-quarters of the signal 25.53 Chalmdford (England) 5.8.W. to the valve. We apply - rather less.
And when the setting is half way wo apply a good deal less than 1986 Baudong half the signal strength to the valve, provided, that is, that the resistance of the patentiometer je about 100,000 ohms. With a lower
I resistance instrument,éb effee and NAVONCE
fret nearly so marked.
19.98 Pittburg
If you draw the circuit you will see that when the potentiometer is ast anywhere but fall on, the grid of the valve has a resistance in i series with it. This roxistarice in
10,102, Daily 6.80 p.m. to midnight
16,304 Daily 7.p.m.:
17.880 Daily, 8 pm; to midnight. 17,7618days 7 pm; & midnight 277
18,404 Each afternoon
19.220 Daily 4,807 p.m.
W8.X.K. 31,640 Not regalar
[Allowance must be made for: “ emmmer-time " in, most Euro- pean countries, which is one hour ahead of true time.]
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