Notes for Beginners:

Radio Record, Volume I, Issue 21, 9 December 1927, Page 13

Notes for Beginners:

By

M.I.R.

E.

Batteries and Power Supply Explained

ROCEEDING: further with the. question of the supply of power for radio receiving sets of the multi-valve type, one of the most talked about and most interesting questions automatically comes up for review, ‘That is the question of the elimination of all batteries and the provision of apparatus capable of supplying the radio set direct from the power mains. To the lay mind it undoubtedly seems’ an extraordinary state of affairs that, with power to burn (in every sense of the word) in a house, the honseholder has to invest a comparatively large sum of money in purchasing batteries for providing more power to run his radio set. The bold statement that the house supply mains do not supply the correct kind of current is an unsatisfactory statement to many of an inquiring turn of mind, and a salesman is frequently called ypon by prospective purchasers to justify his statements concerning his inability, to. supply moderately priced equipment to plug straight into the light, or power socket. _THE PRODUCTION OF SOUND Lo WAVES, , Briefly, radio signals are made audable IY virtue of electrical effects mduced in the antenna system bein amplified and then ‘‘detected,’? amplified again, and then passed through head telephones or loudspeaker, where they become audible as sound waves. The sound waves are set up in the air’ by the movement of a metal diaphragm, and this is caused to move by being attracted in a greater or lesser degree towards a magnet, whose strength is varied in proportion to the amount of current arriving from the radio set, It thus follows that the greater the movement the greater the volume of sound, The greater movements of the diaphragm do not depend however, of a large volume of current arriving from the radio set, but depend on greater "variations" of current to cause large variations in the diaphragm. A large volume of current could thus be passed through the sound reproducer without any sound resulting at all, providing the current remained constant in volume or was at a continuous pressure.’ Immediately the pressure or volume is varied, the diaphragm coinmences to vary its position and disturb the air, thus affecting the human ear. by setting up air waves.

MAIN CURRENT UNSUITABLE. | } While no signals are passing through a radio set, therefore the speaker should be quite silent. ‘This would not happen if power were taken from the light or power mains, because this type of current is not continuous, but ts alfernating in pressure fifty times every second, and if such power were used it would set up a very loud, lowpitched note having a periodicity of the before mentioned figure. In the city of Auckland, direct or continuous current is used for power supply by this term as applied to its actual continuity is purely a relative one. For power or lighting purposes, it certainly is "continuous" enough, but not for radio, because it is full of irregularities which are quite insufficient to make a lamp flicker, for instance, hut are so tangible to the hearing when produced in a loudspeaker that the required signals are entirely blotted out, Equipment has been procurable for some time which will smooth out these irregularities, but great care must be exercised in the purchasing of D.C. (direct current) battery eliminators, or ‘Socket Powers," and a guarantee should be forthcoming from the dealer who is supplying, that the ontfit meets the regulations of the Public Works Department, as well as those drawn up by the Fire Underwriters, because some of then: are dangerous. Where the design is an approved one, there is no more to be feared from them than any other domestic appliance. Where AC (aiternating current) is used, the problem becomes a more complex one because this type of current does what its name suggests, and that is, alternates in direction, thus making it definitely discontinuous, because it has to rise to its full pressure from zero in one direction, and then fall to zero before it can reverse to rise to its maximum in the other direction. Consequently two operations have to be performed to make such current supply a radio set. First, the current flowing in the wrong direction must be reversed, and second the gaps existing in the supply filled in . Trom the foregoing it will be seen that an outfit capable of delivering cur-

rent from the supply mains to the radio set carries out no unimportant or mean nerformance, and to do it reliably and efliciently, the purchaser must realise that he is in the same. position as the. prospective purchaser of a receiver, and that is that he must only purchase products turned ont by makers who are known to be reliable, and he should only purchase through a dealer who is prepared to guarantee his apparatus against mechanical defect for a reasonable period. Research is concentrated on this problem of finding an economical method of supplying power supply for radio sets cheaply and reliably, and the problem so far as the "B’ battery eliminator is concerned, may be reckoned to have been solved. Up till a year ago the factor of obsilescence had to be considered, but that dav has passed, and although many important improvements of methods and design will materialise, the eliminator is here to-day in a form which is thoroughly efficient and well worthy of the attention of the set owner or purchaser who is sick of, or doesn’t want to be loaded with, the queer tricks which a radio set gets up to when attached to run-down batteries. SPECIALLY:-DESIGNED RECEIVERS Owners of multivalve sets (meaning from 3 valves upwards) are strongly recommended to discuss the question of quitting their batteries with a _ radio dealer, and adopt the eliminator or socket power. Specially-designed receivers definitely modelled for use with A.C, mains supply are being talked about, and are certainly due for production. In fact, there are one or two types already available on the market. It may be safely said that the orthodox style of receiver with standard designs of socket powers show all the features necessary to convince those interested that this new design exhibits nothing in the way of an improvement. It certainly demonstrates another way of arriving at the same result, but incidentally does it without any lessenitig of apparatus or cost. Un-

questionably interesting developments will -take place along these lines in years to come, but revolutionary improvements will have to show up to warrant a swillg-over from existing ideas. The real problem in the supply of power for radio sets is the question of A supply for the filaments. For technical reasons it is impossible to apply the same principles of obtaining "B’"’ power, ‘the method of smoothing and filling-in the irregularities of the current will not work in this case owing to the low pressure and large volume required demanding a design of smoothing apparatus which would be of such mechanical ‘proportions as to be im practicable of adoption, THE "TRICKLE-CHARGER." The popular method of solving this problem to date has been the adoption of a combination of what has become generally known as a "trickle-charger" and an accumulator battery. The term "trickle" is descriptive enough to convey a meaning of its method of performance without further detail. When the receiver is in action, the battery is supplying power, but when the receiver is switched off the battery is taking a very small charge continuously from the mains, and the rate of charge is designed to replace in the battery what thle receiver absorbs with average usage. To all intents and purposes this is a complete solution of the problem because except for a periodical examination of the battery, the owner can forget his battery troubles and sympathise with his less fortunate neighbour, who may be seen making heavy weather once a fortnight towards the nearest charging station, and alternately getting a. heavy list to port or starboard, according to his changing over his accumulator from his left to right hand as his arm tires. From the point of view of economy of initial outlay, the trickle-charger and battery combination is going to be the most popular design for many a long day to come. ‘The same comaan shee ET

bination in its more flexible designs as described before, in the shape of & straight-out accumulator of standard design, with a charger capable of put ting a charge of considerable, but regulable, size into the hattery, is uns doubtedly the best from point of view of ultimate life of bats tery. This is unquestionably the opinion of those who understand bat« tery maintenance, but the results are dependent on the user keping the battery in a charged condition, and not permitting it to be run right down, With the trickle-charger the capacit of the battery is usually low, and if unusual demands are made on the re4 ceiver by, leaving it inadvertently, switched on, or by continuous runs ning for any legitimate reason, thext the output may exced the input, and the receiver will just simply go ont of commission pending a supply slow; ly building up again in the. battery. Good types of trickle-chargers have means for adjusting the charging rate, and under such circumstances the. hate tery should stand up to its overload, It will be appreciated that, from the point of view of minimum amount of: worry, the A eliminator, or. socket power, of the trickle-charge design is certainly the best offering eat presents THE PROBLEM OF "A" POWER. It was mentioned previously that de+ velopments were in train which were designed to produce a special type of receiver, adaptable to consumption of energy from A.C. power mains, AS was also stated before, no very marke ed improvement was likely to result from such developments unless r-volus tionary discoveries were made. | The same may be said to apply to a simi4 lar application of principles to the furnishing of A power. Tn order to ‘apply these principles at all, thé otthodox method of assembling thé filament supply circuits has had to be altered, thus rendering this class of supply apparatus useless for standard machines. Furthermore, special valved have to be nsed. ; hese remarks should not be preted as in any way condemnatorya The new system will find its own place. If it is not a success, them the place it will find will be the same as many anti-static inventions of the past, and that is oblivion. The sys tems in general vogue to-day are tried and true, and guarantees of success and service may, therfore, be madé and received with mutual good-will. ED ~ aes