Servicing The Multi-Valve Radio Set

Radio Record, Volume I, Issue 25, 6 January 1928, Page 5

Servicing The Multi-Valve Radio Set

How Money Can Be Saved on Little Details

(By

M.I.R.

E.

An oft forgotten point with the would-be listener is that the radio set, like every other mechanical contrivance, requires a certain amount of expert attention during its lifetime. The necessity for having this attention given it by the agent of the set, who is, naturally enough, the man most conversant with its various features, is stressed in the following article. Set owners are also shown how they can save money through acquiring a knowledge of many of the small points connected with the efficient running of their set,

From the point of view of the layman there is a halo of mystery surrounding the happenings which take place imside a radio set. There is really no need for such a condition of -affairs. ‘That a little knowledge is a dangerous thing is undoubted, but a little knowledge is a necessity for the creation of a perspective and providing the littl knowledge is gained the right way, an intelligent application or use of it may be made. Willy-nilly, the average citizen of today possesses a perspective of the principles of internal combusion engines through seeing and hearing so much of motor-cars, The gramo- . phone and many other machines in daily use were, not so very long ago, enshrouded in the same halo of romance that to-day causes so miatiy people to run up servicing bills for themselves and the dealers. The question of servicing has received consideration in these columns on previous occasions, and set owners have been besought to allow no one, but the recognised agent for their particular make of machine to touch their. equipment, and to especially keep the so-called expert from meddling. This advice holds good even vin face of the concluding statement of the preceding paragraph.

The day has not yet arrived when the radio set or the motorcar can be purchased and cun for ever, or even a year, without attention of some kind from skilled hands. — Face this fact when purchasing, therefore, The attention required will not amount to much. nor cause the owner to suffer inconvenience. The expense of maintenance connected with the running of a_ Ssixvalve set, for. instance, over the period of a year will approximate £5 to £6, including license fee as well as a couple of valve renewals. This amount refers of course to installations which draw their. pow- | er from current laid on in the house, "either directly or indirectly,. through batteries dnd chargers, Where there is no power available and the equipment is fed from dry batteries with "dull-emitter" valves, the expense will increase to about a total of £10 per annum. (This is equivalent to 8d. per day, which is surely reasonable enough to brighten the soul of even the classic but mucli-maligned Aberdonian.)

SAVING MONEY. These charges may be reduced somewhat by eliminating an amouut reckoned at thirty shillings as representing two or three service calls on the part of the dealer. These calle will be occasioned by small things gone wrong in the shape of a broken battery connection caused by a duster in the hands of an over-enthusiastic housewife, or a failure on the part of the owner to recoguise symptoms of faulty reception easily traceable to a run-down battery, etc. Briefly, therefore, the points to be observed are as follow: Purchase only standard apparatus which carries with it a guarantee of service. (It 1s to be noted that this does not mean free service. Free service will not be given enthusiastically because it means 60 much los§ to the dealer. Paid service never pavs the dealer, but reimburses him for his out-of-pocket services, SO that as a consequence he will be willing to give lasting service.) Let no oie but the recognised agent of the recciyer touch the machine. RECOGNISING FAULTS. Certain makes of machines or certain models of a given make have their weak poitts. (Nothing is perfect in

this world, so don’t expect it in radio ot anything else mechauical), a certain fault will periodically develop. Get the dealer to tell all about it so that it may be recognised promptly when it occurs again anj the proper corrective applied without worrying the dealer, If he’ is told frankly that it is appreciated, that it is inevitable that minor faults will occur from time to time, and that it is not desired to bother him every time it will be found ‘hat be will lay himself out to give all the assistance, hat lies in his power, Jie dealer handling the make of machine in question gets invaluable experience, and a perspective of troubles which will enable him to give salient points which all be invaluable in enabling set Owl ers to get not only satisfaction, but real satisfaction and pleasure because an appreciation of the fact that the installation is doing its job properly. Various points of valuable but general interest have been given in these columns before, regarding the proper type of equipment to use and how to remedy certain main defects. It is palpably impossible to depart from a consideration of generalities because there are so many varied types of sets and accompanying accessories available and in use. .

--. CHECKING THE SET. Three things of prime importance to the average set owner are a_ voltmeter, a hydrometer, and a spare valve, The voltmeter gives a ready check on the batteries, whether they be of the accumulator or dry-cell variety. EHlandy meters of pocket size and resembling a vest-pocket watch in shape, are available for round about £1 or less. Such a meter usually has three terminals, one vest being used for measuriaz the A or filament battery voltage and the other pair (one terminal, the negative, being common to both pairs) 1s for measuring the ‘‘B," or plate, kattery. Such a voltmeter has two scales, usually, one marked OQ-6, or 0-8, and the other 0-40, or 0-5O. volts. Care must be taken not to connect the ‘"B" battery to the low voltage terminals, ot the voltmeter will be put out of commission. In measuring the voltage of either an accumulator or dry battery, but especially the latter, it is of the utmost necessity to do it "on load." That is to say, the set should be switched on full; so that the batteries are in

operation while their pressure is being taken If dry batteries are in use the set should have been in full operation for about fifteen minutes before the readings are taken. Do not forget this, because under any other circumstances the readings are no indication whatever of the condition of the batteries. In the case of accumulators, a drop in voltage below the normal is always an indication of a necessity to charge. If it is necessary to send the batteries to a service station to be charged, then a 20 per cent drop in voltage is permissible, but no more. If a charger is available on the premises

always keep tle batteries up to full voltage, The batteries accompanying a standard radio set consist of three, commonly known as the A, B, and C, or filament, bias and plate batteries, The second goes as high as 200 where a power valve is used, but its usual pressure is 90 to 100, and the C may range from 43 volts up to 45 or even more. A drop in pressure of any of these batteries will result in distortion and set noises, while any deficiencies of the first and third will become more pronounced tf the second becomes faulty. (More especially if dry -batteries are in use.)When testing with the voltmeter, therefore, the voltage range of the meter shonld not be exceeded. The 0-6 or 0-8 range will cover the A battery, or a 3 or 4}-volt bias battery. For everything else the B_ battery scale, 0-50, should be used. A battery of 90 volts will invariably consist of two dry-cell blocks of 45 volts each. Hence each half should be

measured in -determining the _ total pressure. THE B ELIMINATOR. Where A or B_ battery eliminators, or ‘"socket-powers,’" are in use it should be noted that voltmeters are no indication of output unless the meter is an especially good one, as only laboratory types are of such efficiency as to come under this heading. The reason for, this. is simply explained. A voltmeter, although it reads voltage, or pressure, nevertheless consumes a certain amount of current in pulling the pointer round the scale. In a cheap or even reasonably priced instrament, this amount of current is ---

equivalent to that taken by several valves and it is beyond the capacity of the eliminator to turnish it, especially, in addition to’ that flowing through the valyes if the set is turned on at the same time. An eliminator supposed to furnish 100 volts for instance may, only show 650 voits simply because it can only supply sufficient current te pull the pointer half-way round the scale and not necessarily because it is not giving tull voltage. The best way, to test an eliminator is to obtain a "characteristic curve" of the valve or valves in use. These curves are quite simple and 1f one is not supplied in the packet with the valve, there will be a leaflet showing bias voltages to be used with certain plate voltages. Héte is where the dealer’s advice is invaluable, because he can give the necessary figures in such a way that a rapid and simple test may be applied with ease. An audio amplifying valve invariably has 90 to 100 volts on its plate. At this voltage 8 to 44 volts bias is necessary. When the bias is reduced to 13, if any distortion which has crept into the signals promptly disappears, then the voltage has dropped to probably 60 on the plate. With 100 volts on the plate the bias should be increased to almost 6 before any "‘scratchiness"? of signal shonld be noted, while at 73 the signals will be all broken,. Naturally these figures ate merely typical, and will vary according to the difs ferent types of valves in use. In our next issue it is proposed to continue further with this discussion, but it showid be noted that the latest designs of receivers are no longer fitted with voltmeters because of the increasing popularity of socket powers and the misleading readings an average voltmeter gives in combination with sucly outfits