1931-05-21 — Page 2

HONG KONG DAILY PRESS, THURSDAY, MAY 21, 1931,

TADIO

AC-SG3 Set

ENTIRELY MAINS OPERATED

A sensation in 8 valvo 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 distant stationa.

Price only

$145.00

Including Mazda. Valves (the best British Valves)

Special B ELIMINATOR for any "domestic: 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 “PERTRIX" 150, 100, 80, 45 volts and C. batteries.

Ebonite "TROLIT" and Pressed Fibre Fanels cut in any size. Loudspeakers,, and various parts are also obtainable.

For further information apply to:-

CANTON TRADING ASSOCIATION, LTD.

CHINA BUILDING (5TH FLOOR).

TELEPHONE 24610.

Hear the Golden Voice

FROM THE NEW

FEATURES

CHOOSING THE RIGHT RESISTANCE.

WATTAGE RATING: CURRENT CAPACITY: VOLTAGE DROP.

Resistances are employed to a for A.C. sets. To some extent this to remember is that 1,000 ohms will very large extent in the make-up is a matter of trial and error. Sup. produco a voltage drop of 1 volt

of a modern radio set, and thero are now so many types and such widely different uses that a few remarks on the subject will be of interest. Perhaps one of the first points which we may discuss is the rating of the resistance from which we can gather the current which can be safely handled. Many manu- facturers, particularly in the case of the spaghetti resistances which are becoming prominent, rate the resist ancos in terms of the current which can safely be carried. This is really a more satisfactory procedure than giving a wattage rating, since ono only requires to know the watta dissipated in a relatively small núm- ber of cases. The item of practical interest is the current which can safely be carried.

pose, for example, we wish to design a serica-feed resistance for the anode circuit of a detector valve. If we assumo, a certain voltage on the anode of the valve and and the corresponding anode current we can then determine the value of resistance required in order necessary voltage. to drop the Usually the resistance works out ab an odd value, and we have, there fare, to adopt & resistance slightly greater or slightly smaller and the conditions will automatically adjust themselves.

per milliamp. Hence, if we wish to drop 100 volta with 43 milliamps our resistance will ́ba"

100

-- × 1,000 - 22,500 ohms.

4'5

odd course, This is, of

tho value,

nearest stock sizes

an

being 20,000 and 20,000 (23,000

cerned this little precaution will often make all the difference he tween a dirty joint and one in which you can take an hopest, pridé.

CLEAN SOLDERING, curves of the valve (or to charts); ́ whence we find the anode current

Cleanliness saves much bed ten corresponding to 30 volte bias and the anode voltage in use. Let us per and language when there is a 19sume that this is 14 milliamps. job of soldering to be done. Ons By the application of the same should always have a pices of salt rules the required value of resist cloth close at hand, and use it to ance can be readily worked out, and wipe down cach joint whilst the

Here again This prevents the usual greasy de- ealculation shows that the actual flux is still liquified by the heat. value is 2,140 ohms. this is an odd value, and the ques- posit from forming during cooling, tion arises na to whether it is neces and saves the joint from being the sary to be exact, or whether a 2,000-happy hunting ground for all sortö ohm resistance may be used. Again ; of dirt, dust, and fluffi which is not, an netaal nominal 2,000 ohm re- easily dislodged once it gets a foot- sistance may perhaps vary by 5 per ing. So far as appearance is con cont, either way, so that the ques tion of the necessity for exact values is an important one .......

Fortunately, an automatio adjust ing process takes place in the valve just as with a series-feed re

NEW MAZDA VALVES, Suppose we use 2,000. ahms instead of the 2,140 which is a 110 volts on our anode. The in-sistance.

There seems to be no limit to creased anode voltage, however, will theoretically necessary. The effect enuse a rise in the anode current of grid bias, a little less than the the surprises which the valve unnu- which is thus no longer 4 milli-30 we require. The immediate refacturers have in store.

sult will be that the anode current amps, but something a little larger. will increase, and this in turn will contly we have received a Mazda ho increased anode current will cause an increased volage drop on PP5/400, which is a valve of posi- cause an increased drop in the feed the bias resistance, giving an in- tively amazing characteristics. It creased grid-bias. Consequently resistance, giving us something

any tendency to increase the anode iz provided wth a 4-volt Slament more than 10 but less than 100 volts current will immediately be check taking 2 amperes, and is designed drop. The conditions will auto-ed, and the valve will settle down for an anode voltage of 400.

to operate at a voltage a little less

and the amplification factor 0, giv determine the anode current which the anode current produces sufficiented, but not seriously different.

In fact, it would probably being us a mutual conductnace el 0. the valve will take with 100 volta voltage drop on the feed resistance found that if the resistance were as milliamps per volt. I

We checked on the anode and with the correct to make the anode voltage corretti as 1,500 ohms, the grid-bins

would only be a few volts different. these figures, and found them ear- Amateur Wireless. grid bina-f.e., the grid bias which spondent to the anode current. we are proposing to use in this particular instance. Let us say

Let us assume that we have a valve on which we wish to place an anode voltago of 100, and that our supply is 300. Therefore, we wish to drop 100 volts on the feed resistance. From the valve clairne-

chi are available sometimes.) We shall not bo seriously out if wa choose a 20,000-ohm resistance. At first sight it would appear that this would only drop 50 volts giving use

Just re-

The

It does not follow, incidentally, teristic or from suitable tables wematically adjust themselves, so that than the theoretical 30 volts requir. internal resistance is 1,300 ohms,

that a resistance will dissolve inte n cloud of smoke if the rated current is exceeded, and usually an over- londed of at least a 100 per cent. is possible. It is not desirable to exceed the rating, however, for long periods, owing to the strain which is placed on the fine wire employ.that this works out at 4 milliampa ed. Switching on and off involves

which is, of course, accompanied by

Now the voltage drop on a resist ance is obtained, by multiplying

Grid-bins resistances for A.C. valves are designed on just the same principles. Here it is desired to produce a certain grid, voltage, which is obtained by making uso

rect.

The construction of the valve is ingenious. The flament is 10 in. long, arranged in four V-shaped loops. Around this is the grid, and surrounding the whole is an anode in, wide, and in thick. The strength, and is stayed to give it robustness. The support is gener

us, and the robustness of the gen- eral construction is strikingly ny- parent

an alternate heating and cooling the resisting by the current in of the voltage drop produced by the ing to get too much out of the built up like a box, 2 in. long, 13 expansion and contraction of the amperes. Since we usually work in anode current of the particular serew at the back of the instrument anode is ridged to give extra

wire. If the current is doubled the heating will be increased four times, so giving a much greater range of expansion and sooner or later the wire will break down under the strain.

The wattage rating is a measure of the dissipation of heat. Beeist- ances are stated to have 5, 10, or 20 watts dissipation, and from these the current capacity must be work- ed out. We can, for example, have a range of resistors the values of which run from 5,000 to 50,000, nil rated at the same wattage; yeb they will not all carry the same current. The 50,000-ohm sample, in- deed, will only carry one hundredth of the current which the 5,000-olun resistor will carry in order to dis-

ATWATER KENT RADIO cipate the same wattage. The watta

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SOLE DISTRIBUTORS.

dissipation is the product of the resistance itself and the square of the current carried.

Suppose,, for example, we have a 50,000-nhra resistance rated to dis sipate 10 watts. We should work dut the maximum safe, current in the following manner;

Watta 10 (Current) * x 60,000

.. Current==

10

20,000

014 amps, 14 milliamps.

Incidentally, it should be remark- ed that in most cases, particularly with high-value resistances, the rated wattage is never reached under normal geonditions, as the voltage would be too high..

milliamps in radio practice it is necessary to multiply by the milli amps and divide by 1,000, and in this connection a very simple rule

valve.

Let us suppose here' that we wish to produce 30 volts grid-bias. Oneo again we refer to the characteristic

HAVE YOU HEARD THESE?

Here are lista of long-wave and short-wave stations which should be picked up by anyone in Hong Kong who has a moda- rately good set suitable for re- ceiving such signals. Success in picking up these stations also depends very largely upon fav- ourable atmospheric conditions, Readers are bvited to add to this list should they succeed in picking up any station net in- cluded in either of these flats.

LOUD SPEAKER RATTLE, "Rattle is usually caused by try loud-speaker. 1 the adjusting is turned so as to reduce the clear nuce between the Arnantare and the pole-picces, the sensitivity of the One then gets speaker increases.

At 400 volts the valve will handle louder signals for a given input, but any extra strong note will almost certainly cause the armature about 32 volls grid swing, the anode to strike against magnet. The re- current being 65 milliamps. Under undistorted medy is to turn back the adjusting these conditions an screw a little. The light loss in power output of five watts is pos signal strength is more than com-sible, this being obtained with an pensated by freedom from chatter. anode load of about 3,500 chips, Sometimes, of course, rattle is We have had ne much ne five waite caused by a screw which has work from output valves before, hut ed loose under vibration. If so, never have we been able to produce the offender can usually be traced such an output with only, a little without much trouble and tightened over 30 volts grid swing-Amateur

Wireless. Call

Kilo up. Sign cycle KZ.I.B. 1,153 K.S.M.8. 1,085 C.R.C. K.R.C.

LONG-WAVE STATIONS.

Wave length (Metres) Station

200 Manila 277 Shanghai 180 Tientsin 310 Shanghai

320 Peping 345 Toyo

1,070 087

C.O.P.K. 045 J.O.A.K, €170 353 Hiroshima J.O.P.K 250 355 Hong Kong Z3.W. *337. Bombay V.U.B 381 Sapporo J.0.1.K. 830 305 Keijo

370 Nagoya 370.4 Calculta

840

840

J.O.D.I. 820 J.O.C.K. 610 V.U.C

380 Kumamoto J.O.G.K.

300 Senda! 365 Dairen

308 Rangoon 400 Osaka 410 Canton 413 Manila

SHORT-WAVE STATIONS.

"STATION

CALL SIGN

07.05 Dobiata (Germany) A.F.K. 0012 Khabarovsk (Russia) RAVI,

Nauen 50.7 50. Mosco

BT: $2.5 Sydnoy 81.85 Melbourna 81,48 Behonectady

CTCLEA

୫୦୫.୫

נאד

J.O.FL.K. 770 J.D.A.K. 700 734 V.U.R. J.O.B.K 760," C.M.B. 728 KZR.M. 796

T (Hona Hoxo)

or WorkinO

4484 Mon, Wed. & Pri.. 6 p.m. & 2 mm.

4,000 || 5-10 p.m.

6,000 Thor, Thurs., Ext., 8 p.m.

A.G.J.

5201 Not regular

R.K.N.

1.M.A.

a.&.c.

V.B.1.A.B.

6,896 Bunday midnight

7,142 Dally 8.80 p.m. & 11 p.m. ⠀!..

7,810 Not regular

7,730 Daily 1

8,108 Tues, & FRAK

$220 Not regular ...

9,503 | Not reguler,

9,530 Daily 7am-

pm-1 a.m.

9,620 FTL 8. Bat. 8 am, & 10 m.

43.5 Rome,

2 41,3

Forth

Singapore

88.8 Kootwijk (Holland)

Bangkok (Binm)

P.C.L. H.9.4.P.J.

2.B.J

W.9.X.A.F.

81.20 Eladhoven (Holland) P.C.J.

2.F.C.

7.L.0.

Z.M.E.

10,628 Not regular....:

P.Lih

11,020 Midnight- am daily

Saturday and Sunday

12,260 Nightly

13,850 4. Wod, Fri, Sat.

.27.8

In the case we have just consider ed the voltage developed across the resistance in order to dissipate 10 watts would be 700 valta, a much 81.28 Sydney higher value than would be obtain- 29.6 ed in normal practice. In passing, it may be also be remarked: that a resistance rated at 10 watts should be capable of withstanding this voltage without any risk of a break- down of the insultation.

So much for the rating. The next question which we have to consider is that of the voltage drop across ühe resistance and how we are” to determine it. This is often of im portance when designing series-feed resistance and grid-bias resistances

31, Nairobi (Konya) Byday... Bandoeng 25.53 Chelmsford (England}|6,8,W,'-

Manila 20.86 Bchenectady 18.88 Baudoang 16.4..

245

Kootwijk (Holland) 17.4 Bandoeng.....

Bangkok

FIXE. W.2.X.O

PLO

POL

:1

P.L.F.

9,500 Not regular.

5,077 Midnight daily pi

11,761 7.80 p.m. & 8 am, dally, except

10102 Daily 6.80, p.m. to midnight

10,804 Daily 7 p.m..

17.280 Baily 8 p.a. to midnight

17,761 Sundays 7 pm & midnight

19,404 Ench afternoon.

19,220 Daily C.30—7pan

10,861 Daily 3.0.

W.8.K.K.21,540 Not regular

H.8.1.P.J. 15.0 10.3 Kootwijk (Holland): FC.E 16.74 Bandoong

18.5 Nancy (France)

12.08 Pittsburg

PLE

(Allowance must be made for "summer-time" in most Eure- pean countries, which is one hour ahead of true time.]

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