THE WIRELESS WORLD.

Otago Daily Times, Issue 20963, 28 February 1930, Page 5

THE WIRELESS WORLD.

NOTES AND RECORDS. By Magna Vox. Items of local interest are invited by Magna Vox”, for publication in this column. It is necessary that such matter should reach this office by Tuesday of each week for insertion on the following Friday. _ Metres 7ZL, Hobart .. .. 535 3AR, Melbourne , .. .. 484 4YA. Dunedin .. „ .. .. 463 2FC; Sydney 442 2YA-. Wellington .. .. .. 420 . tQG* Brisbane 385 jLQ. Melbourne 371 2KY, Sydney .. .. .. .. 289 2AH Sydney .. .. ~ 316 2KY. Sydney .. ~ .. .. 280 ANSWERS TO CORRESPONDENTS. “ Cui," Omakau.—The trouble probably lies in your transformer, and I should advise you to have your set forwarded to the agent, and have it tested. Whistler,” Palmerston. —Reduce the voltage placed on the detector valves, and see that the speaker is not placed on top of the cabinet or facing the valves. Place the cabinet on shock „ absorbers such as sponge rubber. “Kiwi,” Dunedin.— (1) The aerial-earth system, including ae it, does unductance capacity and resistance, has certain well-defined characteristics and properties which may quite easily have effects on certain frequencies. I should say that your difficulty could be removed by including a small variable or semi-variable series condenser in the aerial circuit. (2) Evidently there is feed-back, but it is out of phase, and thus _ cuts down signal strength. A similar effect may be noticed when a reaction coil is wrongly wired. Check the layout and wiring carefully, altering the position fo the coils, etc. J.M.R., Dunedin.—Several, things might be causing the whistle you complain of. ■ Firet- try reducing the voltage on the detector. If this is not successful, try reversing the primary of one of the transformers (especially if the transformers are of different \ makes). Try a .002 fixed condenser across the secondary of the last transformer as a bypass condenser. If you have not an R.F. choke in series with the plate lead to the first transformer, try one. See that your B battery is not run down, and that the transformers are placed at least four inches apart and mounted at right angles. Keep the plate and the grid leads well apart. The last audio valve, or the grid condenser and leak may be faulty, or there may. be an open circuit in the grid portion of the receiver. RADIO EXHIBITION. The Otago Radio Association proposes holding another exhibition, commencing on April 29 and continuing until May 2. The Pioneers and Early Settlers’ Halls have been engaged, and as applications for space are already-coming in, it looks as if the venture, will be even more successful than the exhibition held in August last. RATIO OF LICENSES TO DWELLINGS. !An interesting compilation was made recently by the Australian Broadcasting Company to ascertain the ratio of licenses to dweljings in the capital cities, and the various States of the Commonwealth. The ratio of licenses to dwellings in the cities is; Sydney, 1 to 5; Melbourne, i to 2: Adelaide, 1 to 5; Brisbane, 1 to 3: Perth, Ito 22; Hobart, !to 10. The ratio for the various States differs slightly from that of the cities, and this is as follows: —New South Wales, 1 to 6; Victoria, 1 to 3; South Australia, 1 to 8; Queensland, 1 to ff; Western Australia, 1 to 23; Tasmania, 1 to 13. BATTERY HINTS. One .of the commonest causes of the gradual deterioration of the quality and volume given by a radio set is the lack of attention given to the. batteries operating in the various circuits. . The filament;’ or A battery, second, the plate, or B battery, and third, the C grid bias cells, u order ’ to . understand why attention should be paid to the .various batteries, we will see what effect the variation of each has on the quality and volume of the sets output.. Assuming that the B battery and C battery are in good condition,* and that the A battery is running down, we shall find that the received music or speech begins to get weaker and i weaker without any great loss of quality, until, if the A battery is eompletely discharged, no music, or speech at all will be heard. There is no need for this to happen if the battery is regularly tested with an hydrometer. Make a point of testing the batteries every few da >'s, a mi keep a record chart of their condition, and the hours of use. Another use for the hydrometer is to efteck up the battery after it is returned from being charged. Never allow the A battery totally to discharge, or remain digciiJirced for a long period. ' The next battery to consider is the plate supply, or “B " battery. If th» other in . order, and the B battery yoltage is reduced, a decided falling off in quality and volume will be observed. If the battery is of the dry cell type and is fairly old, and the other two batteries are "known to be in order, what will be_ noticed is that on switching on the set, signals are fairly loud, though perhaps the quality is not so good as it had been before, but after a time the signals become weaker, and the quality becomes worse. This is due to the B battery becoming discharged, and recuperating to some extent in the periods in which the set is not used. Of course i these batteries should have been discarded before this happens, but it is difficnlt, it not impossible, to know when to replace if no means of measuring are available. For this purpose a voltmeter will be most useful. The usual type of voltmeter requires a current to operate it which, although very small, is quite sufficient load in itself for testing a B battery. The B battery voltage' on the set should be kept within 10 per cent of the intended voltage, if really good resultsare required, and the dry battery should be completely discarded when it shows a reading of less than two-thirds of Us rated voltage—before this, if it can ■be afforded. It will be found that it is. very expensive to run a loud speaker set of three to five valves with the cheap small capacity dry battery if good quality is to.be maintained, since with a heavy load these little batteries last for so short a time, and it is more economical to use the long-capacity type, which, although they may cost two or three times as much, will last five or six times longer. If the plate supply is drawn from accumulator B ■ batteries, a 90-volt battery should not be allowed to discharge below 80 volts before being charged again. When testing the voltage of an accumulator B battery, do so after the set has been in operation for about five minutes. Occasionally test the gravity of each cell in the battery.

The remaining battery, the C or grid bias cells, is one which usually receives little or any attention at all, although it certainly requires the least of the three It must be remembered that a dry battery does not last for ever, even if no current be taken out of it. In fact, a life of 12 months under these conditions is all that can reasonably be expected. The electrolyte in the battery gradually dries up completely in the course of time, rendering the cell useless, even if it is .not used at all during the time, so that the grid bias battery should be renewed as a matter of course every nine mouths. The voltage, as shown on a meter, will decrease gradually owing to the increase of resistance of the battery, due to drying up of the electrolyte. If the grid bias to the audio amplifier value is too small, or becomes too small, serious distortion will be noticed, and a serious drain on the B batteries will take place. Also, the life of the valves will be materially shortened. It would not be out of place to point out the .great importance of carrying out the valves manufacturers’ advice as to providing the correct grid bias for each stage of amplification. The usual all-purpose valves require in the vicinity of nine volts grid bias, with 135 volts on the plate. But if a power valve is to be used in the last stage, it will be found that the manufacturer recommends 15 to 22J volts bias. To conclude, if you do not possess a voltmeter and hydrometer, purchase one, and make a point of testing your batteries regularly, and keep a chart of the hydrometer and voltmeter readings, so that you will know when your A batteries want charging, and the B batteries renewed. If these suggestions are carried out, the radio will always be in good condition for special broadcasts you may want to hear.