1931-07-23 — Page 2

HONG KONG DAILY PRESS, THURSDAY, JULY 23, 1931.

Listen -

RADIO

If you want Best British Components, it is undoubtedly

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THE SINCERE Co., LTD.

SOLE DISTRIBUTORS,

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- geiving much signale, Saccess in picking up these; stations also depends very largely upon fave ourable atmospherio conditions, Readers are invited to add toʻ this list should they succeed in -plaking up any station not-in-

cluded in either of these lists.

LONG-WAVE STATIONS.

Wave length (Metres) Station 250 Manila. 277 Shanghai

FEATURES

A.C. VALVE DEVELOPMENTS.

A BRIEF REVIEW OF THE POSITION OF THE MAINS VALVE.

Almost Incredible.!!

During the last few years valves with an impedance round about volts anode potential. These are have altered a ver great deal. 6,000 to 2000 ohms. Their efficiency has rapidly becz increasing, until to-day there in no doubt that the' British valve is the best and most efficient in the world in fact, it is so efficient that a large number of manufacturers seem to have difficulty in designing appara tus that is good enough for the

valves with which it is to be used,

A few years ago nobody thought very much about using the rains

Economical to Run.

The indirectly-heated screened- grid valve is really too well-known to need much discussion here. The A.C. screened-grid valvo in a really

',

THE SILVER MARSHALL.

OUTSTANDING FEATURES OF THE SUPERHETERODYNE.

Wing On Co., Ltd., that they have designed to have an exactly op With the announcement from the sated for by employing a speaker 4-volt flament valves having a file A.C. Superheterodyne Receivers, posite frequency characteristic, and just received a large shipment of ment consumption in the case of the manufactured by the Silver-Mar- which nicely boosts the attenuated shall Incorp., Chicago, USA; frequencies up to their original 24A of 275, and in the

of the

ranging from the small midget to levels as far as the car is concern 24B (which is really intended for the large console, acts are now cd, and the car, after all, is the

Available from stock,, Minal judge

The Silver-Marshall midget super-

(d)-Sensitivity. The sensitivity heterodyne, though midget in size test found on 8-midget superhet (chassis only 12"), it is a giant in is far better than any tuned radio ing designs for the year. The en vary from 8 to 10 microvolta performance, has all the outstand-

frequency set. The sensitivity 'curve On the super, numerous DX distant (n.)-Eight-tube Superheterodyne one rotation of the dial; abso modela may be classified as follows: stations could be tuned in with model consists of a dual selector lutely without interference or cross Chassis. The circuit of this now. circuit preceding & UY224 screen talk, with no antenna or ground, grid first detector, A27 oscillator and with far less noise than on inductively coupled to this detee the tr.f. set.

A.Ç. work) of 1 amp.

Mesars, Cossors have an extra valve in their A.C. series when

efficient circuit can be made to give compared with the other mains A..gineering features for advanced

almost as much magnification as two really good battery valves, and will, moreover, be much more economical,

valves, for they have an R.C. type which has an impedance of 20,000 ohms, and an amplification factor of 33. The other arme simply go to derive the whole of the power: All the well-known valve frmain for the screened-grid, B.F., L.F., for a radio receiving set, but nowa, have gone in for A.C. indirectly and the power valves. daya A.C: valves have so altered heated valves, and though some of This R.C. valve is not an R.C. the complexion of things that any the firtas also market directly-heat-valve in the true sense of the word, body having alternating-current ed A.C.. xaves, there is usually no for the impedance is quite low, and mains supply misses. a very great comparison between the two types it makes an excellent detector or opportunity, unless he uses A.C. from point of view of, efficiency. H.F. in ཉ་ neutralised circuit. valves in his receiver.

Recently the Mazda, and Mar-

For ordinary work, where the coni, and Osram groups re-issued last degree of magnification is not their AC. indirectly-heated valves, nceded, one would use the H.F. providing even finer characteristics with 14,000 bhms and a magnifica- than before. Mutual conductances tion factor of 32 rather than the are going up everywhere, and Mul higher mag, valve for detector pur- lards, and Six-Sixty, have reached the alpost. incredible mag-factor of 1,500 and 1,000 with impedances of only about 430,000 ohms. This, as you will see from any catalogue of magnification factors and mutual valves, is far and away above the conductances of some of the later effeiency obtained by the battery of these wonderiu! battery valves S.G. valve.

rival the Bgures obtained with some of the A.C.'6

Not only are these valves econ omical to run from the point of view of power taken from the mains, but they are tremendously eficient; a good two valve A.Ceet should give just as good results as the ordinary three-valve battery

receiver.

That is saying something, but | A.C. valves are really in a class of their own as regards the magni- fication per stage which can be got out of them.

Just let us look at a few figures. The average A.C. detector valve has a magnification factor of 35 as Call Kilo against an impedance of anything Sign

cycle from 10,000 to 15,000 ohms; whilst KZL.B. 1,188

the first LF. valve may be of the K.S.M.S. 1,088 345 Tokyo J.O.A.E.. 670 -

sarac type, or it may be slightly 333 Hiroshima J.O.F.K. 850 larger," giving an amplification 355 Hong Kong Z.B.W." 840 357.1 Bombay

factor of something like 18 to 20 .V.U.B. 840 301 Sapporo J.O.LK. 830 368 Keijo J.O.D.K. BRO 370 Nagoya J.O.C.E. 810 370.4 Calcutta V.U.U 809.9 330 Kumamoto J.O.GE. 1790 300 Sendai J.O.HX.

770 J.Q.A.K. 760 J.O.B.K. 700 C.M.B. 789 K.Z.R.M.

305 Dairen 400 Osaks -410 Canton 460 Manila

SHORT-WAVE STATIONS,

STATION

CALL BIGN

67.85 Dobintz (Germany). A.F.K. 60.12 Khabarovsk (Busila) | BA97

50.7

Хадери

50.

Моко

48.5 Rome

41.3

Parth

CICLES

Trum (Hono Kowa} OF WORKING

025

4,484 Mon, Wed. & Fri., 6p.m. & 2 a.m 4,000 0-10 p.m.

6,000 Too, Thurs., Sat., 8 pm,

7142 Daily 6.80 p.m. & 11 p.ni 7810 Not regular" ****

AG.J.

6,291 Not regular

B.F.N.

IMA 4.4.0,

6800 Bunday midnight

Singapore

88.8

Kootwijk (Holland)

Sydney

37,

22.

Bangkok (Siam)

21.66 Melbourne

81.48 Schenectady."

7.780 Daily 11 p.m.

V.9:1:A.B. P.O.L. HSAPJ. 9,109 Tues, & Fri, 9 pm-1a.m. 2.B.L.

0,230 Not regalar 3.1.0. 9,503 Not regular WAKAF 0,630 Daily a.m. 9,620

81.30 Eindhoven (Holland) PCJ 31.28

Sydney

BL...

39.6

Nairobl Sydney

Trobi (Kenya)

27.9

Bandoeng

2.F.C.

7.1.0

2.M.E. PLRY 25.53 Chelmsford (England) 5,8.W. 240 Manila

28.85 Schenectady

Kootwijk (Holland). Bandoeng.

W.2.XO,

18.89 Bandoeng

18.4

P.LLG. P.C.L.

174

PALF

18.9 Bangkok

168

Kootwijk (Holland).

16.74 Bandoeng

$19.99 Pittsburg

16.5 Nancy (France) 2,

Allowance

peza, countries, which

Fri. 8. Sat. 3 am) & 10 am, - 9,400) Not regular

9,677 Midnight daily 10,620 Not regalar

11,020 Midnight am daily 11,751 7.80 p.m. & 3 a.m, daily, except

12.240 Nightly

Saturday and Sunday

12,860 4.m. Wed, Fri, Sat.

16,102 Daily 6.20 p.m. to midnight 10.304 Daily 7 pm.

17.230 Daily 8 pm to midnight

17,781 Sundays 7 pm, & midalght (18,404 Each afternoon

18.1.PJ ROK. PLE 19,220) Dally,~,307. p.,

10,861 Dally, 8 mm, 2 W.8.X.K. 21,540 Not regalar

summer time in most, Euro- one hour ahead of free time.

·A· GRID-BIAS TIP."

Then there is e Mazda A.C. Pen., an indirectly-heated valve which has an amplication factor ofĮ semething like 95, and which is capable of handling "quite a lot of power.

Mallards have come very fine directly-heated pentodos in the 244 and 24B, the former of which takes

poses.

But the A.Q, valve will have to look to its laurels, for the 2-volters are gradually creeping up and the

The Latest Rivals,

grid i.f. amplification. & UY227 order to give entirely adequate tor, two stages of UY224 screen-(e)-Local-distance Switch-In second detector, two UX245's in a control even on powerful local single push-pull audio output stage.. stations, the local distance switch and an UX280 rectifier.

is included. In the local position features of the receiver it would ground with a 200 ohm resistor, Before considering the design the switch shunts the aerial and

THE SILVER MARSHALLA

be well to examine its performance such as selectivity, fidelity and son

sitivity.

this effectively reducing overall gain for local reception.

(f)-Tone control. A midget (.)-Selectivity. The recciver

condenser ur .025 mid and a vari- which is uniform to within less comprise the tone control, which will give absolute 10 Kc. selectivity able resistance of 500,000 ohms. broadcast band, since it is deter-notie at will, by the rotation of the than 10 per cent, over the entire varies the high, low and triple mined almost wholly by, the if resistance knob. to suit the taste of amplifier selectivity and the listeners. 77 "Arithmetical selectivity. The i...

12

transformer is tuned to 175 K ()-Full Tone Dynamic Speak

matched which is the ideal i.f. for super-er-Specialle.

electro- heterodyne designed for the broad dynamic speaker with full tone For instance, we have the Mar from a stability and select

cast band of 550 and 1,600 Ke. quality is used for faithful repro- selectivity duction. One section of the electro- coni L.P.9/C which has an imped-point.

dynabia speaker field acts as the (c)-Fidelity. That is, antenna filter choke and the other section of ance of 4,000 ohms and the surpris to speaker, while the true story is the speaker field serves as the grid, ear sound bias resistor automatically bitsing ing magnification factor of 8. An- pressure measurements which would the UX246 pash-pull tubes.

told by antenna to:

other remarkable 2-volter is the Mullard P.M. 2A, an output valve

a grid bias of 21 volts at 300 volts which has an impedance of 3,000 anode, and the latter bise of ohms and a magnifiention factor of something like 35 to 40 volts at 400 12.8, Some figures aren't they

+

.. FOUR-VOLT FILAMENTS,

The Electrical Standardisation

Committee recommends the use of 4-volt filaments for all radio.reeciv ing valves; it also suggests that a uniform size of bulb is desirable.

has been conducting his television experimenta over a period of five

the executives of the Crocker First years with the financial backing of

National Bank here. Mr. Farne- worth said that he is preparing to start at once for Philadelphia where

F:-%-bkti,Rt,""་"ལྟ་ -n h༑

When you are watching the milli ammeter used to track down the distortion caused by overloading you can learn more from it than the mere fact that distortion, is or There is no doubt that the present ho will erect the first commercial is not taking place from this cause system of marketing & 4, and television station. He said that | Incorrect grid bias means that the evolt valves is both complicated the broadcast of the television he working point in either too low or and uneconomical. Other things has perfected is clear for a dis- too high on the grid volt plate cur- being equal, the d-volt valve can be

tance of 50 miles and that it can rent curve. Should it be too low designed to give a slightly higher bottom bending, will take place, amplification factor than the 2-volt This means that you are over-bias-type. But, since the introduction of ing and the milliammeter will re- the screen-grid valve this margin of cord the fact by upward kicks. On differnce has become relatively un- the other hand, too high a working important. The adoption of a 4-volt standard is. reasonable compro-

い

point means grid currenting. The miss which, by favouring mass-pro- grid bias is too low and the milli duction methods, should help in arameter kicks downwards. You time to lower pricer.

can, therefore, adjust the grid hins

carefully, and if the milliammeter-

with won't steady down

Gay grid bias that you give the waive then you know that the straight portion of the curve is too sroft, and that you want a valve of lower im

NEW SYSTEM OF TELEVISION.

he carried any distance by tele phone wires and then be rebroad- cast over another 50 miles radius..

RADIO TELEPHONE EXTENSION,

(BRITISH WIRELESS SERVICE.

RUGBY, July 91,

The Postmaster General announces that from Thursday, July 23, the San Francisco, July 11-Teleradio telephone service will be vision without discs and making use available between all parts of ɑreat only of tubes has been perfected, Mr. Philo Farnsworth, an inventor,

Britain and Northern Ireland and

announced to-day. Farnsworth all parts of New Zealand.

include compensated speaker. The same chassis is used in the The fidelity ourve in the 6-M" Compact" and "Consoletto midget superhet. is to be fat to models. The line voltage supply cycles, and to fall off rapidly up AC, 30/00 cycles, but other voltage Iess than 4 decibles from 60 to 1,000 for these models is 110-120 volts tn 4,000 cycles, the limiting, fre for 200/250 volts AC, 50/60 cycles quency necessary for faithful, re- can be furnished with minimum production. This fall off is compen-cost

Silver

Marshall

Midget

Engineering Features

FOR

Advanced 1932 Models

Superheterodyne 8-TUBE SUPERHETEHODYNE

RADIO

CHASSIS (3-SCREEN-GHID &

2-245 TUBES

TONE CONTROL LOCAL-DISTANCE SWITCH EXTENSION SPEAKER JACK TEN K.O. SELEUTIVITY : SENSITIVITY REDUCED

NOISE LEVEL ILLUMINATED

DRUM DIAL FULL TORE

MOVING COIL SPEAKER

No REPEAT POINTS

No OSCILLATION

COMPACT SIZE

FOR FURTHER

CHASSIS ONLY 12

THE WING ON CO., LTD

28671

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