A Corner for Beginners

Radio Record, Volume II, Issue 20, 30 November 1928, Page 10

A Corner for Beginners

By

Observer

A Little Appreciation. Manx thanks for your kinduess in dealing with my queries as set out in this week’s "Radio Record," also for the fullness of the information given. Wishing. yourself and the "Corner" oath) success,- "Sonora" (Lower Voltage on A Battery. M set ig a two-valves; I use one eell, a dry battery to light both valves. Is this sufficient, or should each valve have a separate battery and rheostat. Would two or three of these A ,batteries connected in series be better or would you advise a different type of a battery --Beginner (Palmerston North). As with all A batteries, the most important question is, "What is the voltage and consumption of the valves in use?" With regard to the first great care should be exercised to ensure that the current on the filament is not at a voltage higher than that recommended by the makers. As the correspondent does not state the valves he is using it is impossible to answer his first question; he should find out what voltage his valves require, then reckon. each dry cell as 14 volts. Valves except in certain circuits are connected in parallel with one rheostat. Where a valve requires a lower voltage than the rest it should be supplied with a separate rheostat of a high resistance. Where more than two valves are in use, it is not wise to use dry cells. Even in circuits of one or two valves dry cells should not be used if the total consumption is greater than about 12 amperes per hour. When consumption exceeds this an accumulator should be employed preferably with a trickle charger. There are two important points for the beginner to keep in view: 1, Valves requiring different filament Voltages should not be used unless adequate precautions are taken to protect the filament of the valves requiring the lesser voltage. The voltage required is that of the valve requiring the highest voltage, not their sum. 2 The consumption is that of the Sum of each valve added together.

Types of Aerials. iA CORRESPONDENT, M.W.Y. (Wellington), who has not read our rules, sends the following queries to "Pentode," who answers only those questions referred by "Observer," to whom all technical correspondence must be addressed -- | "Which of the following aerials is the most efficient-given that gauge of wire and other considerations re. main constant: "1. One length of 100 feet. Lane

"2. Two parallel lengths of 50 feet -(a) 6 feet apart, (bd) 3 feet apart. "3. Four parallel lengths of 25 feet, 3 feet apart." Many beginners no doubt ask themselves this question, and finally arrive at some solution, whether right or wrong. Here is the accepted solution. The two wire aerial of a given length will always bring in stronger signals than the single wire, other things being equal. Three wires would bring in stronger signals than the two-wire sgerial, but there is no semblance — of proportion, eg., two wires would not

give anything like twice the volume of one wire, although an increase in length would give rapidly increasing signal strength. That is to say, it is preferable to increase length than to introduce more wires. Wires too close together serve no purpose, the optimum. distance being six feet. Above this nothing is to he gained, while, when the wires are not separated by six feet, little is to be gained by the extra wires. Applying these facts to the questions asked: One wire 100 feet is preferable to two 50 feet. Wires separated by 3 feet are less —

suitable than wires six feet apart. Four parallel lengths of twenty-five feet. would be the least efficient. Loose Coupling. A CORRESPONDENT has asked the meaning of the term "loose coupled," and as it is one of the most common of. radio terms, it may be worth a little explanation. The term refers to the proximity of coils, not to the method of connection. with the terminal, as our correspondent suggested. Around every conductor, charged with electricity, there exists a field BESSA EEE Eee PPE EE Lf ETP PRIS Ee PE

of magnetism, through which signals can be passed as through the conductor, The extent of this field is ‘hot very great. Coils or any other conductor placed in this field will pick up the signals from the other conductor. In this manner a connection exists between them, ie., they are loosely coupled. Coils placed very close to one another are said to be tightly coupled and strongly influence one another, This magnetic induction, as it is termed, may, if mot properly controlled, seriously interfere with other conductors in the set and cause distortion. This explains shielding and space winding, and the separation. of certain components such as transformers, coils, and condensers. ° Valves Failing to Light. I HAVE a factory-made wireless set, and it has given every satisfaction up till lately, but about four weeks ago, while moving the volume control towards soft, signals stopped, and I found that a valve had gone out and wouldn’t light for some time, but: trying the set next evening everything worked all right, though if I touch the volume control out goes the same valves every time, or if it does not go out it flickers down very low and stops reception. Now, sir, knowing nothing

about grid bias and such things, I can’t give you such information, but I would be very pleased if I could get .« to know more about the set I am using, as I hardly know’ anything about the valves, so I might be mistaken in. saying it is the power valve that is causing the trouble, but I will give the positions of them. [From the diagram it is the radio or high-frequency val & at. fault.) 7 Last night 1 noted a new kind of static, so I tested the 3 B batteries, and they read 29 volts, 89 volts, 50 volts or more. Could you tell me how this happened? Don’t the B batteries drain alike?’ How did the 45-volt block get to 50 or more when I tested them separately ? I bound the eads of the A battery terminals with fine sand-papered copper wire, for about an inch and I never get any of the fine strands of the leads broken or jammed when screwing on the top of the terminal."-F.H, (Westport). : THIS is just the type of letter we want-no matter how elementary the problem is, we welcome it. In this particular receiver the high frequency valve is controlled by a separate rheostat, or dial on the receiver. If. for some reason this valve refused to light, one of three things may be suspected: (1) That the A battery was too low. (2) That the rheostat was not working properly. (3) That the valve was broken. From what our correspondent says, it appears as if the rheostat is faulty. Perhaps it. has worked loose, and does not make a good connection, ‘"Observer" has had that happen often to bis set, Maybe there is a loose or broken connection between the rheostat and the valve or between the valve and , the A battery. = F.H, would be advised to proceed as follow:-Disconnect the batteries, examine garefully the rheostat to see that there is nothing loose, likewise examine the wires coming to and from the valve and rheostat, Anything loose should be tightened. | Artificial Static.

REGARDING the second question, artificial static. A. short time back we spoke of this being, an indication ‘that the B battery was low. On putting a voltmeter across his batteries F.H. finds this to be. the case, Twentynine volts is too low and should be replaced. As the different blocks supply different valves, requiring varying amounts of battery, they run down at different rates. Grid. bias supplied ‘by. a small _ battery within the set is applied to the grid of the valve to regulate the flow to the plate. If this battery becomes too low it should be replaced. A grid bias registering 25 per cent. below normal should be replaced. The cost is trifling, but the effect is the reverse. " Some batteries certainly register above their rating, but these are uncommon, The suggestion about binding the ends of the wires is a good one-ywe commend it to all readers. Directional Effect. QEB, Northland, writes :-I have tried two: indoor aerials, one consisting of talking ‘tape strung across the room} and passing over another which coxnsists of four copper wires separated at each end by a wooden cross and. the lead taken fromthe middle, The result was that the talking tape worked

Wonderfully about R8-9, while the ether ene would not work at all. The reception from the upper was very bad when the lower was ‘taken down. While leaving the lower up and working the set from the upper reception was three times as good as that from the outdoor aerial, The lower aerial had an insu- , jator at each end, while the upper had 4 none, i There are several points to consider in this question:- . (1) Directional effect. From a diagram supplied the aerials run in different directions. The talking tape may be directional to 2YA and the -wire aerial not. , (2) The four eopper wires unless separated by six feet would not act as four separate aerials, It appears they were not far apart suv that they were acting as one only, {3) The upper wire being the stronger, acted as a blanket and inducted the signals collected from the lower, thus augmenting its own signals by signals which were not in themselves strong enough to be heard. (4) The outdoor aerial was possibly faulty and -undirectional. Getting the Americans, "FT).M." (Te Wera) writes: "I am using a five valve factory-made set with a power. valve. 2FC, Sydney, I can get any’day and any time they. are broadcasting, that is, from 9 a.m. until they sign-off; sometimes only a whisper and other times loud enough to hear in the room with loudspeaker. All New Zealand stations are a good bet for me to get any day they are broadcasting. Plenty of volume. After nightfall the volume from New Zealand and Australians is enormous, in fact have to detune. -i am using a good high aerial; lead-in not soldered, and short earth wire clamped only _ to a small pipe. driven into the gipund. I am using 90 volts wet B battery with 45 volts dry attached. Why cannot I get any stations outside New Zealand and Australian after nightfall?" . . There are several considerations, any of which might affect the reception of distant stations, the most important are (1) Direction of aerial. To receive the Americans an L aerial should run from N.B, to 'S8.W., with the leadin at ‘the N.H. end. -To receive the Japs an aerial running N. and S., with the lead-in N. would be the most directional. A compromise ‘to get good results from each could be easily effected. (2) These stations are heard usually late at night or in very early morning. Try burning the midnight oil. Speaker Polarity. "[ WISH to know," writes "HL.L.W." (Glen Oroua), "if you could give me some advice on the following :-I have just made a three-valve set, and on connecting the speaker in the usual way (red cord to B-+-) the tone and volume are very poor, harsh and rattling. If I connect the speaker the other way round with the red to the jplate of the last valve the tone is improved, also the volume, and I ean get ‘more distant stations. I applied the test for. .polarity given in the "Radio Record" for November 2, and the correct way by this is with the black cord ‘connected to B+. ‘Hoping you can let me know about this, as I do not wish to damage the speaker by running the set wrongly connected,"

The test is proof that there is a mistake in the wiring of the speaker. It is quite an easy thing for those assembling the set to put the black wire on to the positive pole instead of on to the negative. The correspondent is correct in joining the black to the B--, provided the test has proved it to be the positive speaker terminal. His is evidently one.of the cases where the wires have been wrongly connected to the speaker. This letter points to the necessity for ‘listeners to test their speakers for polarity, as the colouring is not infallible, and damage can be done by a wrong connection. Volume Control. "YVOULD you kindly advise ‘me, through the columns of the "Radio Record" on the following matter? I have a factory-made set, and until lately was using valves of high consumption, I then changed over to the other valves to economise on A battery consumption. I got improved reception and greater volume, but I am unable to shut off the rheostats sufficiently to quieten the set. Could you advise me of a method in which I could overcome this difficulty?"’W.K. McK. (Glen Massey). Volume control was fully dealt with in our issue of October 12, to which our correspondent is referred. Another method is to incorporate another rheostat in the filament circuit, making two in series, An Efficient Earth. "THE same writer from Glen Massey sends the following description of an earth which we pass on to readers for trial and report :- ,"E have also installed a type of earth which I consider has improved the efficiency of the set wonderfully, and which I consider may with advantage be adopted by many listeners. J sank a hole 6ft. deep and filled it up with elinker and cinders. The diameter of the hole is 3ft. I then spaced seven #in, galvanised water-pipes an equal distance apart around the hole, leaving the ends prortuding above the surface of the earth about 2in. I then procured a length of seven-strand insulated wire and attached one strand by an earth clip to each pipe. The earth wire leading from the set was then soldered to the end of the ground wire, close to the set. Hach galvanised pipe was bored with four 1-8in. holes, and the ends of the pipes being open allow the water to be poured down them, thus keeping the clinker around the pipes in a moist condition. This earth gives first-class results." Connecting A and B Batteries. A CORRESPONDENT has asked "which is the best way to connect the ‘A’ and ‘B’ batteries together, the A--to the B- or the A-++ to the B-?’ The system which is considered best in most receiving sets is one in which the A-++ and B- are connected together. When these two terminals are connected together the effective B battery voltage is increased by the amount of voltage of the A battery.