1931-04-30 — Page 2

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HONG KONG DAILY PRESS, THURSDAY, APRIL 30, 1931.

TADIO

Hear the Golden Voice

FROM THE NEW

FEATURES

PURE TONE--AND HOW TO GET IT

HIGH-FREQUENCY AND DETECTOR SIDE OF SET CAN CAUSE DISTORTION.

Grid-Lolk ValuES. If for some unaccountable reason, set won't give good undistorted

Formerly a 0003 grid condenser results when firat made up, or if and a 2-megohm leak were used it deteriorates after a while, the without any question, but with some average owner immediately suspects of the new detector valves more the low-frequency side or the power satisfactory working is to be hnd

ATWATER KENT RADIO supply. This is because he realises with a slightly lower value of grid

our

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that if the high-tension drops the leak, say one-megohm or even less, purity is bound to fall off, and and a grid condenser of smaller that if, as power valves do not capacity, say .0002. improve with age, the output cap abilitics of a sot decrense after while, it is the low-frequency side) which should be suspected.

If you suspect that detector stage of your set is causing distortion, then you can try a 1-megohm grid leak and you can also fit n .0003 pre-set condenser in

In this way it is often overlook- maximum

tion.

impedance valve of about 10,000 ohms.

Power Detection. With any of these non-distorting schemes there is a snag and in the case of power detection there is the

trouble that with a valve of a low impedance, working with a more appreciable positive bins the anode current may be as much milliamperes, and an H.T. voltage of 100 or even 180 may be called for.

·

AS

B

This current may be sufficient to upsot matters if the set is to work on a battery or an eliminator hav-

ing a fairly limited output. The extra 6 milliamperes is, unfortu nately, often a costly matter; but

that is not the end of the trouble. Transformers following ordinary de- tectors are designed to give good

ed that the high-frequency and de-pince of the present fixed conden- tector side of a set can equally ser. The pronet condenser costs well be the cause of a bad distor only a few peace more and you have the advantage that you can Just consider the detector valve, alter it to suit the valve and de- first of all, because the points here tector eirenit. Once upon a timei obviously apply to any set which it was quite common to have af has a valve detector. The average variable grid conden, but within characteristics with the usual small general-purpose set has a grid con- the mst few years we have, un-D.C. current flowing through the denger and lenk and practically the fortunately, regarded the leaky grid primary. When the anode current in pushed up to 5 milliamperea only exceptions to this are high detector circuit as beyond improve though, Hs it is with power quality sets which are made difment-which is certainly a mistake. detector circuit, the transformer Power-grid detection, like anode primary may be overloaded as this ferently with anode bend reétificu

steady D.C current saturates the detection,

withstand tion, or super-hets, in which it is bend

core. The result of this is that the customary nowadays to have the greater signal voltages than the impedance of the primary winding first stage of detection arranged on ordinary leaky-grid circuit with the of the transformer is reduced, be

cause of the less effective iran core, usual values. anode-bend lines.

and then distortion creeps in.

•

cnr:

Then, of course, there is power- A power-grid detection circuit bas grid detection of which many people the same conections as the leaky- speak, because it is a comparatively grid, but a still smaller condenser, modern craze, without knowing .0001 microfarad as a rule, and much about it.

still smaller grid, leak—about megohm-are used. It is import ant, too, that the valve should have the right impedance, and with these

It is, unfortunately, only too easy to overload the average leaky-grid detector. The grid of the valve

}

is connected through the leak values it is general to have a low. to the positive side of the filament and a small amount of grid current flows. One is apt to pay too little attention to the proper values of

FL

£

Because this saturation is not con- stant; the distortion is not constant, and the cure, of course, in to fit a transformer designed to have, suitable primary inductance value at the higher D.C. current of 5 milliamperes; alternatively, you can ton by-pass circuit with an L.F. choke designed to carry this cur rent or, in some cases, a resistance may be used.

(Continued on Page 31)

the grid condenser and leak, and HAVE YOU HEARD THESE?

it is forgotten that in order to pre- vent distortion due to the grid cur rent flowing the values of the grid condenser and leak have to be chosen with care.

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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- calving such signals. Success in picking up these stations also depends vary largely upon fav ourable atmospheric conditiona. Readers are invited to add to this list should they succeed in picking up any station not in- cluded in either of these listu.

LONG-WAVE STATIONS.

WAVE length

Oыll Kilo- Sign cyale K.Z.I.B. 1,13 K.S.M.S. 1,088 C.R.C. 1,070 K.R.C. 907

(Metres) Station

200 Manila 277 Shanghai 980 Tientsin 310 Shanghai 220 Peping 0.0.P.K. 845 345 Tokyo J.0.A.K,

870

353 Hiroshima J.O.F.K. 850 355 Hong Kong Z.B.W. 840 397 Borabay V.U.B 840

J.O.I.K. 301 Sapporo 308 Keijo

370 Nagoya 370.4 Calcutta

800

3.O.D.K. 800

J.O.C.K. 810 Y.U.C

380 Kumamoto J.O.G.K.

390 Sendai 305 Dairea 398 Rangoon 400 Osaka 410 Canton

413 Manila

SHORT-WAVE STATIONS.

STATION

CALL SIGN

67.85 Dabinte (Germany)

A.P.K. 6013 Khabarovsk (Bussia) | KA‚07.

43.5

30.8. Kootwijk (Holland) P.C.L.

25.53 Chelmsford (England) 6.8W,

Kito

Сте

809.0

700

J.O.FL.K. 770 J.D.A.K. 780 V.U.R. 754 J.O.B.K 760 C.M.B. 739 KZ.R.M. 720

Thx (Hong Kona)

OF WORKING

4,424 Mon., Wed, & Fri., 6 pan, & 2 am

4,000 6-10 p.m.

5291 Not regnier.

6,000 Tue, Thura, Sat. 8 p.m.

7,14 Daily 6.30 p.m. & 11 p.m.

7,310 Not regular

7,730 Daily 11 pm.

8,109 Tues, & Fri., & pm-1 am.

9,530) Daily 2.10.

9,620 Fri, 8 a.m., Sat.. 3. a.m. &.10 mm, 1

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44

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APPLIANCE

66.7.

A.0.3.

69.

Moscow

EVN.

Kame

1.M.A.

0,600 Sunday midnight

42, Porth

¡C.A,Q.

+1,3 Singapore

V.E.L.A.D.

37. Hangkok (Siam)

H.SAP J.

32. Sydney

$1,66 Melbourne

2.0.5. 3.1.0...

0,200 Not regular

0,608 Not regular

31.48 Bebenectady

W.3.K.A.F.

31.30 Eindhoven (Holland) | P.C.J.

91,28 Sydney

2.F.C.

9,500❘ Not regular

31.

Nairobi (Kenya)'

7.1.0.

9,077 Midnight daily

26.5 Sydney

2.M.E.

10,620 Not regular

218 Bandoeng

PL R

11,020 | Midnight——3 am, daily

K.1.X.X.

12,240 Nightly

24.5 Manila

23,35 Echenectady

18.88 Bandoerg

TELE. FUN

18.4 Kootwijk (Holland) 17,1 Bandoeng 168 Bangkok 10,3 15.74 Handoeng

Kootwijk (Holland)

16,5

Nancy (France)

13.93 Pittsburg

[Allowance must be made for !! summer-time !! in mort Euro- pean countries, which is one hour ahead of true time.] -

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Washing Machines Cookers, Grillers Appliances for the Tollet ete

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11,751 7.80 p.m. & 8 a.m. daily, exsent

12,960 m, Wed, Fri, Sat.

10,102 Daily 6.80 pan. to midnight

16,304 Dally 7p...

17.280 Daily 8 pm, to midnight

17,751 Sunday 7 pm & midnight

18,404 Each afternoon.

10,220 Dally 5,30--7 p.1.

F.C.K. PLE

10,851 Daily 3.

W.9.X.K.

21,540 Not regular

Saturday and Sunday

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Pedestal Hester Suppiled with ayda, flexible cond and B.C. adaptor