Page
HONG KONG DAILY PRESS, FRIDAY, DECEMBER 25, 1931.
RADIO MA
EVERYTHINGE.C. ELECTRICAL
our guarantee
GECOPHONE ALL-ELECTRIC RADIO SETS
and.
RADIO GRAMOPHONES SPEAK FOR THEMSELVES.
DEMONSTRATIONS DAILY from 11.00 a.m.
All apparatus to the value of £5 or over can be supplied on hire purchase terms.
Free service for 3 months
G.E.C. SHOWROOM Queen's Building, Chater Road). Hong Kong.
Osram Valves
PURITY OF TONE
THE
SINCERE
LIMITED.
CO.,
THE LARGEST RADIO DEALERS
IN HONGKONG & S. CHINA
SOLE
AND
AGENTS,
DISTRIBUTORS,
FOR
PILOT RADIO & TUBE
CORPORATION
LAWRENCE, MASS.. U.S.A.
THE LARGEST
RADIO
PLANT IN THE WORLD
FEATURES
FOR THE NEWCOMER TO WIRELESS.
VARIABLE CONDENSERS AND IMPEDANCE.
There are several types of vari able condenser, aren't there ?
Yes, there are no less than four
available at the present time,
What are they? There's first of all the original
straight line capacity pattern. Then we have the square-law, or straight-line wavelength. Next there is the straight-line frequency and thatly the logarithmic.
Which is the best to use We can rule out the straight-line- capacity condensed for tuning pur poses to-day,
How is that?
Since in a tuned circuit the wave-
-length varies as the square of the capacity we must quadruple the capacity to obtain double the wave- Jength.
I follow that.
#
If we double the capacity the wave-length is increased not twice, but the square root of two times, which is roughly 14 times.
What is the besult practically 7 It follows that whether we work.
in wavelength or in kilocycles, the calibration chart of any circuit pķo-
(vided" with this kind of crindenser will always show a curved line. The exact shape of the curve cannot be
determined unless the reading for" very large number of stations are
used.
That certainly is a drawback. The straight-line wavelength con- lenser has vanes so shaped that the further and further meshing of the moving with the fixed; produces į a regular increase in the WATE- lengths to which the circuit is tuned.
Which means
That if two stations are tuned in, one of which requires a dial read- ing of, any, 30 divisions and the
other one of 80 divisions a coli-
ting condenser readings, against wavelengths in metres and ruling
a straight line between the two
points.
1 begin to see what you are after. The square law condenser gives as wido separation of stations on higher wavelengths but producca bad drowding at the lower and of the band.
Then for general use you would recommend nowadays the straight line frequency condenser.
In most cases, I most certainly trould. But there is one important
exception.
Please explain.
If you look at a family of valvo hourves you find that characteristics are plotted for different plate volt. ages. In that of the P410, for exam-
ple, there are curves for 75, 100,
123, and 150 anode volts.
I seo.
}
In other words, if you compare. the 7-volt characteristic with the 100-volt you see the diforence, pro- duced by a change in plata volta
of 25.
Now, if you look at the family you will see that the plate current with 100 volts II.T. and no grid hias is 15 milliampai · Change the plate Voltage by 23, or in other words reduce it to 75, and the plate our rent goes down to 10. It follows that taking 100 plate volta as a basis, a change of 25 volts produces
I is impossible to make two circuits such as those of a high frequency valve and a detector worka 5-milliampers change in current. quite in step, when either S.I.W. or S.L.F. condensers are used. In other words these circuits cannot be ganged," or be provided with a single tuning dial, with complete
satisfaction."
What is the remedy:
The use of the logarithmic con- denser, which permits the ganging in a very satisfactory way of two or even three circuits. With con-
densers of this type it is possible ́ to effect one-control operation simply by placing small correcting or balancing condensers across cach parato circuit included in the gang-control arrangement.
IMPEDANCE.
To find the impedance we divide 2. volts by .0005 ampere and the an awer is 5,000. Actually, if you have lie, data for the amplification factor and the mutual conductance you can find the impedance at once by dividing the mutual conductance into the amplification factor and adding on three noughts. Here the amplification factor is 7.35 and the matdal.conductance 1.& Again we get the answer. "5,000.
Why do the makers always give the impedance and so on at "grid" bias zero?
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 mode- rately good ret suitable for re- ceiving such signals. Bucosss in picking up there stations also -depends very largely upon fav. ourabla atmospheric conditions, Headers are invited to add, to this, list should they suooped in ploking up any station not in- cluded in either of these, lista. “.
STATION
1
LONG-WAVE STATIONS.
Wave length
Call
Kilo-
(Metras) Station Sign oyale
KZL.B. 1,138 K.S.M.S. 1,083 J.O:A.K. 70
200. Manila 277 Shanghai 345 Tokyo .353 Hiroshima J.O.F.E 850.. 355 Hong Kong Z.B.W. 840 357.1 Bombay. V.U.B. 840 361 Sapporo - J.O.LK., 830
J.O.D.K. 308 Keijo
150 J.O.C.K. 370 Nagoya
810 $70.4 Calcutta Y.U.C. 800.9
380 Kumamoto J.0.G.E. 700 300 Sendai
395. Dairen
400 Osaka
410 Canton 480 Manila
`SHORT-WAVE STATIONS.
CALL SIGN
67.85 Dobints (Germany) A.F.X. 60:12 Ebabarovsk (Bustle) RA97. 58.7 Nationw
41.8
81.48
2.B.L.. 3.L.D..
KILO
CYCLE-
J.0.HK 770. J.Q.A.K. 700 J.O.B.K. 780 C:M.B #70 K.Z.R.M 625
Tins (HONG KONG)
OF WORKING
4,434 Mon, Wed. & Fri., 6 pm, & 2 a.. 4,9006-10..m..
5,291 | Not regular
6,000 The Thurs., Sat., 8 p.m....
8,806 Sunday midnight
7,142 Daily 6.80 p.m. & 11 p.m.
7,810 Not regular .
7,730 | Dully 11_pan,
8,103 Tues, & Fri, 0p.m.-10.m.
9,280 Not enter
9.803 Not regular
9,680 Daily 7 6.01.
0,620.]. Fel. J'am... Sat. 3 am, & 10 am. 9,600 Not regular
9,877 Midnight daily
10,526 Not regular
A.G.J.
50.
Mosco
B.F.N"
Rome
.1.M.A.
Porth
8.A.G.
Singapore
V.8.1.A.B.
88.8 $7.
Kootwijk (Holland)
P.C.
Bangkok (diam)
SAP.J.
32.1
Bydney
81.65
Melbourne Sabenectady
`W.2.K.A.P.
81.20 Bindhoven (Holland)
P.C.J.
31.28
28.0
Sydney
2.F.C.
Nairobi (Kenya)
T.L.O...
Sydney
2.M.E.
Bandoeng
P.LE
28.88
Chelmsford (England) 5.8.W||
Manila
K.1.X.R.
28.85 Schenectady
W...X.O.
P.LG,
Kootwijk (Holland)
P.O.L
17.4
Bandoong
P.L.F.
16.0
Bangkok
16.3 13.74
Kootwijk (Holland)
P.C.K
Bandong
P.LE.
19,220 | Daily..30-p..
15.6
Nancy (France)
10,361 Daily 8 m.
Pittsburg
21,543 Not regular
$7.8
24.0
15.88 Bandceng 18,4
I have often wondered, for these figures are quite misleading. The actual impedance, mutual conduct. ance and amplification factor of a valve are totally different under working. Tonditions, with a strong 13.03 grid bias.. The amplification factor and the impedance go up and the mutual conductance naturally goes Well, perhaps you will tell me down, Another time we will discuss årst of all about plate-filament re-just what the amplification factor
Is valve impedance the same thing as plate-filament resistance!
No. Something absolutely differ
ent.
sistance.
4
That's a varying figure which de- pends upon filament temperature,
ís.
plate voltage, and grid-biasing volt JUDGE TRIES ON KNUCKLE
age.
But it remains constant af
cours for any particular, adjust-
DUSTER:
ment of these three. You find the Mr. Justice Wright showed keen
"bration chart can be made by plot-plate-filament resistance by Ohm's interest in a knuckle duster whien law, simply by dividing plate voltsfigured in a charge of robbery with by plate current. If, for example, violence at Glamorgan Assizes. He a valve with 100 volts on the plate made a close inspection of the wen posses 10 milliamperes of current pon, and having fitted it on t with a given grid bias, then the his hand, conferred with the Hign plate-filament resistance is 100 divid. Sheriff who was sitting on
bench. ed by 01 amper or 10,000 ohms. Those actually are the figures for the Marconi P430 valve, but the im
pedance of this valve is 5,000 ohms
only.
That seems a big advantage.. It is. But to-day we have an other point to consider:
What is that 1 :
I interference is to be avoided it
is frequencies, rather than wave- lengths that count.
How do you mean 7
Well, it has been established that the absolute minimum asperation between stations, if hetherodynes are to be avoided is 8-or 10 kilo cycles. This is due to the fact that broadenst, transmissions, take place not on single sharply defined wave- lengths but on bands of wave- lengths,
What does that involve 7 Up at the top of the broadcast band a 10-kilogycle separation means a wavelengths difference of several metres: Down near the bottom it. means a wavelength separation of
twa metres or less.
I think I begin to see daylight. Valve resistance is concerned with direct current only and valve im pedance with oscillating currents ́len't that so,
That's it exactly. Now as you know an oscillating impulso pro- ducca changing volts and changing currents. To find the direct-current
resistance of the valve we divide the plate voltage" by the plate cur rent. The impedance is found by dividing the change in plate volts by the change in plate current.
I follow the idea, but just what do you mean by the change in plate
volts?
A LITTLE
the
care in setting up. an advertisement often doubles its selling power.|| It is that little extra thought and care, which is given to advertisement drawn up in the office of the Hong Kong Daily Prens which brings good results
every
K.S.1.P.J.
11,020 Midnight-3 a.. nily
|: 11,751 | 7.80 p.m. & B... daily, except
12,240 Nightly
Saturday and Sunday
12,860a.m. Wed., Fri., Sat
16,102 Dally 6.30 p.m. to midnight
16,304 Daily7 p...
17,280
Daily p.. to midnight
17,701 Sundays 7 p.m & midnight
18,404 Ench afternoon.
[Allowance must be made for "summer-time” in most Euro-
pean countries,, which is one hour ahead of trus time.]
Ideal for XMAS GIFTS.
PILOT A.C. Midget Superheterodyne
(Lowest Price Ever. Offered:)
Skilled Radio Experts Supervision
Free Service to Patrons
1982 Model Engineering Features
7-Tube Superhet, Circuit
(Including Multi-Mu Screen Grid and Power Pentode Tubes)
Hair Line Selectivity Volume and Tone Controls
Local-Distance
Switch
Pick-up Connection Moving Coll Speaker
THE WING ON CO, LTD.
TEL. 20671,
Sole Distributors:
TEL. 26672