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HONG KONG DAILY PRESS, THURSDAY, DECEMBER 17, 1931.
A
FOR THE NEWCOMER TO WIRELESS.
FINDING THE PLATE VOLTAGE
I am using a first-stage low-fre-- quency valve just now which doesn't
seem to be working as it should,
How's that?
The makers show that with a plate. voltage of 100 it requires a negative bins of 4.
And, you And ?
If I connect it to the 100-volt tap-
Fifty thousand ohms.
RADIO
FEATURES
aften apply a rather higher negative ENJOY A WIRELESS
Then, at a yough guess with a valve of pretty low impedance you are probably dropping about 30 off which they are based are taken na your 100 volts in the anode resisen rule with negligible resistance. tance.
ip the plate circuit.
-USING-A-SPEAKER-IN--~-
gridbins, than the makery figures i would suggest, since the curves on
How can one measure the real plate voltage-13-2-voltmeter-any- LING ?
Not as a rule, for it may give you an inaccurate rending owing to ita')
omparatively low resistance.
Then what can nu do?
o You can mensure the voltage quite casily with a niliammeter,
ANOTHER ROOM.
I have rigged up a "local station receiver for my family 1 want to be able to arrange things so that they can use the loud-speaker in any
Milliammeters don't measurevolts, que of four rooms, the set, of course, Tene, but by Ohm's law velty remaining where it is. Can you give
CHRISTMAS.
LISTEN-IN TO THE WORLD.
"WING ON HAVE 1932 MODELS
NOW IN STOCK,
ondast hand is well as will the short-wave bands, and brings in all. the regular domestic stations, with volunte, tone, quality and selectivity that will surprise you.
Pilot .C. Midget Superhet.
Ideal for XMAS GIFTS.
A7-the "Super-Heterodyne yon PILOT A.C. Midget Superheterodyne-
A tube Super-Heterodyne you can own in Midget form "for the first time in a midget, Automatic. Volcano Control which holds volume Messrs. Wing On Co., Ltd., enn at any degree of loudness desired all stations--tone enntról, full now offer you from their stocks, on 193 model radio receivers covering vision dial and gramaphone pick up. short and long-wave sets of A. C. connection. These are features you and battery varieties, built by in- expect only in full-sized sets, yet
ping of my high-tension battery and equil resistance multiplied by: eur-me a simple scheme for carrying thi ternationally known radio manufac-Pilot gives them to you in a midget
is wrong
Why, you are not giving l 100 volts on the plate.
No, that isn't at all necessary.
People will have to go into the room
turers, namely, the National S.W.5 instrument:
Superhet, the Pilot Super Wasp and'. Midget 'Heterodyne receivers.
You won't find more up-to-the Universal minute engineering in way super- heterodyne-three of the new b31 Supervariable Mu, new screen-grid tubes,
give it 43 volta negative grid-bins itt In the circuit you know the out! simply goes ont of action,, passing no value of the resistanco and you can! You don't want. I suppose. to be Short Wave, Silver Marshall A.C. signals at all. Can you tell me what measure the current. Rowing through fiable to switch the set on or off from
Thus it is easy to fud the volte all of these rooms? dropped in it. Suppose, for exam2 ple, that a milliammeter placed be: tween the H.T. positive lead of ain which the set is, anyhow, in order circuit and the appropriate balters tapping registers half a milliampere. Then the calculation is 0005 ampere multiplied by 10,000 ohms, o 25 volts.
But I've just told you that I am, You are connecting 14 plate cir. rnit to the 100-volt tapping. I admit! but that's a very different, thing from putting 100 voits on to the plate
itself.
Please explain.
In the plate circuit of any valve there must be resistance, for in couple it to the next you are obliged | to have an anode resistance, or the "windings of a choke, or the primary
of a transformer.
Then those are the volts dropped in the resistance f
Yes. And to find the actual plate vells you simply subtraes this amount from the battery volts for the tapping concerned. "
I see.
I hadn't thought of that.
Then, if the 100-volt tap And where there is a resistance,ving is in use, the actual plate volts
I would be 100-23, or 75. volts must be dropped in it as cur- Bent passen through. Is follows that in a wireless circuit is the netunt plate voltage exactly equal to that of the H.T.B. tapping concerned."
That's it, exactly. Making use of this role you cap so arrange the value of the resistance that you get a fair proportion of the battery volt- |
I begin to see now. This valve is "ge on to the plate of a valve that
needs a nctually resistance-coupled,
high anode potential. What is the value of the reais. Don't forget, though, that where re- tance?
sistance coupling is used, you may
1.
The
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ELECTRICAL
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Free service for 3 months
G.E.C. SHOWROOM Queen's Building, Chater Road, Hong Kong.
sram Valves
for
PURITY OF TONE
to fetch the loud speaker, for I don't Fropose to provide more than one.
In that case it becomes quite a straightforward matter: but first of all, one question about your set.
Fire away.
Have you a Alter circuit in the onput or is there an output trans- former 7
National S.W.5 Thrill Box. The National 5-tube short-wave receiver covers wavelengths from 15 to 530 metres, The circuit com- prises tuned screen-grid high fre- quency stage, followed by a tuned 'sercen-grid detector gad two stages of audio frequency amplâcation in push-pull.
Among the outstanding features is the ase of two Nasional tuning, As a matter of fact, there is nei-
condensers (of 970deg. rotation ther. Please tell me why you ask
equicycle plate), gnnging by a silver If the loud-speaker is connected fished velves vernier drum dial. directly into the plate circuit, the and the new coil forms known as whole of the high-tension direct cur the R.38. the special low loss rent passed by the output valve material developed for inclusive use must go through its windings in the National short-wave pro- mastn't it?
ducts,
Yes, of course..
<
Huntless A.Ç. short-wave reeep. And therefore any leads connected tion is made possible by the use of to the output terminals of the set the National No.: 1880-A.B. Power
must also carry the whole of this
current.
Why, of course.
胡
Unit, designed especially, for that purpose. This power unit has a double section hum dilter, R.F.
What is your plate voltage for the fiter, an electrostatic shield around last valve f
the primary and special balancing
A hundred and fifty, supplied by 4 resistors around the flament wind- super-capacity dry battery.
יון
ings. It is provided with standard
One of these leads goes to H.T., four prong 1x socket for connection whilst H.T. is earthed. Suppose, I to the set.by means of a four wire now, "that you get a short-circuit cable and National connector plug, owing to defective insulation, 'pretty serious results may follow.
** H.T.
Silver Marshall A.C. Superbets,
The S.M Midget Superhetero- | dyne, though midget in size (chassis only 12ins.), it is a giant in per- formance, has all the outstanding features for the year.
But surely even "super battery won't deliver much current
Won't it, just! One of these bat teries in good condition may pass as much as 15 amperes for a few seconds, and fifteen times 150 works Eight-tube Superheterodyne chas.. out at 24 kilo-watts quite enough tosis-the circuit of this new model do pretty serious damage.
consists of a dual selector, a U.X. į
oscillator inductively coupled to this detector, two stages of U.Y.
I see, now, why you recommend an output transformer where extension lends are used.
<
Use either that or a 5lter eircuit, and you are perfectly safe, ginge, the. extension leads carry only a small A.C. load, and that only when the set is switched on.
What wiring system do you recom- mend 1
Having arranged your output cir cuit in one of the ways which we discussed," run a pair of wires from |the loud-speaker terminals of the set to each of the rooms in question and fi in each a small wall-plug socket.
screen-grid intermediate fre- queney ampliâcation, a U.Y. 207 second detector, twę U.X, 9453'e in
a
single push-pull audio output inge, and an U.X. 990 rectifier."
The sensitivity test found on S.M, midget superhet, is far better than any tuned radio frequency sot. It shows a sensitivity of to 10, zniero-
Connect to the loud-speaker plug volts per metre, 10 kiloeyele scler- to it the sockets and the job in Livity, aud ́a fidality charnetcrístic done. If I were you, I wouldn't use flat to a few decibles antenna to car Lordinary twin flex..
Why t
between 60 and 4,000 cycles; this
Owing to the fact that the insulatinsuring practically perfect tone and ed wires are twisted round each quality, to which is added a tone other, the capacity Between them is
quito considerable, and in long leads control to adapt the tone to indivi-. made of this material it may run to dun fasta or home conditions and a figure big enough to cause a cer-
to minimize effects of author tain suppression of the higher notes. What, then, do you recommend t
static. Good quality bell wire does very well, the two leads being arranged
to ran not too close together.
SOUND VALUES:
Full tone electrodynamic speaker together with the rigid. built chas sis are housed in a beautiful con- solette walnut cabanet.
The Pilot Universal A.C., Super. Wasp.
+
The theoretical unit of sound La used in telephony practice' is the "bel
named after Graham Bell. the famous inventor. The practical unit is one tenth of this value and in called the decibel, or transmission unit Taking average speech, as zero, the loudest speech is about 20 as well as thrilling. It has no dreibels above, whilst a soft whisper
NO COILS TO CHANGE. This new receiver with its won- derful wave-changing switch makes short wave reception comfortable
would be about 40 decibels below troublesome plug-in coils, no loose this level. Or, taking the lowest shielda to disturb. You merely turn limit of audibility zero, ordinary a little knob on the front of the act sprach spoken at a distance of half
an inel from the ear of an average to go from 15 to 150 or 360 to 650 listener, would be heard at a relative metres. Imagine; 16 to 650 metres: strength of 100 decibels. One deci On the samme receivers ! The bel is about the smallest difference Universal is a double-duty set, for in sound intensity which can be detected by the ordinary ear
covers the entire 200-530 metres.
two 227's, one 347 power Pentode tube, one 280 reolider, conplete shielding, a rigid, solidly, built chassis. Pilot receivern have every. thing denoting quality, except- high price.
What do
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TzL. 26671.
1932 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 Coil Speaker.
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The 1932 Super-Heterodyne Radios
PILOT
7-tube Midget Model S.145 $200.00
ATWATER KENT 6-tube Compact Model 80 $225.00
ATWATER KENT 7-tube Compact Model 82 $240.00
ATWATER KENT: 7-tube Console Model 87 $500.00 -ATWATER KENT 8-tube Combination
Model 75 $800.00
All above are complète with ticbus and loudspeakers