A COMPARATIVE TEST OF "B" ELIMINATORS AND THEIR CHARACTERISTICS

Radio Record, Volume I, Issue 2, 29 July 1927, Page 6

A COMPARATIVE TEST OF "B" ELIMINATORS AND THEIR CHARACTERISTICS

LECTURE DELIVERED BY MR.

E. W.

MAHONEY

My lecture to-night consists of data relative to a series of tests of B battery eliminators. These tests were taken bver a period of tour weeks, using the one set al] the time, so that they are fairly representative of reception conditions ‘To avoid fiuctuation of the filament, amperite automatic controls were installed so that all var:ations of volume, etc., would be only derived from the B battery supply Four types of eliminators were tried, three being American and the fourth Dutch The Types Used. Type one: Made and assembled in America. ‘This eliminator had a fixed tappinz for the plate supply and a variable control from zero to 45V_ for {lie detector On test it was found that this eliminator was quite satisfactory for a five-valve set, there being absoIutely no trace of hum. I mught state here that the ordinary valves were used 11 most tests, but where it was found that the climinators had stood up to the requirements of these tests, power valves of all grades were used in the last andio stage With this eliminator volume was certainly increased, but the final tonal quality using all six valves was marred bv the Cistinct hum that came throuel, althongh, as I said hefore, on five valves this was not noticeable Owing to these

conditions, no further tests were taken with this one. Type 2: This was an American B climinator kit ready for building up lccally. ‘The guaranteed output of this type was 200 volts for the plate at 85 milliamps. Variable rheostats for the detector and plate supply were incorporated in this unit and worked quite satisfactorily, Tests taken with a special voltmeter showed that the maximum output was 90V for the det and 220V for the plate supply. A series of tests held over a period of one week showed ‘that this eliminator would not conform to the specifications laid down, and there experiments were stopped. Type 3: This eliminator, assembled 1n America, was found quite satisfactory for a six-valve set. ‘here was no trace of any hum coming throngh the loud speaker when the set was on full power Two points were noticed, and they were, firstly, extra tapping for C battery volt ages were incorporated in this type, of a range that was quite unsuitable for the average set, and, secondly, the price was fairly high, This was quite a very good type of eliminator, but the two items before mentioned were not quite satisfactory. | Type 4: This eliminator, made in Holland, was tried ont and found quite satisfactory for the 6-valve set used Two variable rheostats were used to control the outont for detector and plate supply, the range for the det, being:

from zero to 45 and tor the plate supply from zero to 200 volts. Tests on this eliminator were fairly exhaustive, covering a period of nearly three weeks. Power valves of all makes and kinds were used, including the U.X.210, 112, Daven M.U.6 and Philips 605 In ali cases the tontal output was quite clear, with no sign of hum or distortion due to the eliminator The Test. J Test A: The Daven M.U.6 was used in the last stage of andio. Very good tonal qualities resulted, and volume increased. Test B was taken, using the +(U.X.112 in the last andio stage, and

again the output was clarified and it was found possible to reduce the input voltage to 60 vyolts and _ still receive Australian stations at exceptional loud-speaker strength and without the

least sign of distortion. Using earphones it was found possible to still further reduce the voltage to 30 yolts. ‘his resulted in signals being heard with ample volume on the ’phones, any volume above this being more than the ear could bear with comfort. For instance, whilst listening to 4YA, Dunedin, a few nights ago, who were broadcasting a band relay, it was quite possible to hear people whistling around ‘the band rotunda during intervals of music, and on another occasion when Q®BL relaved from the Sydney Town Hall, two ladies in the audience were heard discussine matters regarding dress whilst waiting for the commencement of the programme. ‘his, as I said before, was heard whilst using the ‘phones, and an input of 30 volts on the eliminator Test C was obtained using Philips’ £05 power valve, and the same reception conditions prevailed as in the previous tests. One noint in connection with this test was noticed, and that was that the tonal ontnnt was clearer on this test than the previous one. Test D.-The super power valve 17.X.200 was used in the last stave for the following results, The tonal quali- ties of the set were vastly improved, and it was found nossible to reduce the input of the eliminator under discus: sion te 50 volts, when Australian stations were heard quite distinctly, wor? for word, 40 feet or mote awav from the set. the volume heing sufficient to fill a Jarre ballroom for dancing purposes. This is only a brief summary of tests «nd results obtained, and 1} must now turn to the commercial side of the question and the relative cost and unkeen, and B eliminatots versus drv cell B batteries. Life of Batteries. Using oversize B dry cell batteries and nsing the set for 4 hours a day, with a power valve in the last ptage, the ap-

| proximate life of these latteries is abont six months. So that in one year it costs £6 for batteries alone. Not only that, the user must discard these when the vullage drops to 60 volts or only one-third used, and must suffer considerable annoyance from crackling and rustling noises as the voltage drops and the internal resistance of the batveries increases. On the other hand, a B eliminator costs anvthing from approximately £9 10s. to £17, being three to five and a half times as much as the cost of a set of dry cells, which most of you will admit is a very serious item. Balanced against that, the first cost of an eliminator is practically the last, as it was found that by using the last eliminator the average drain, when using — full 100 volts, was only 8 watts, and that is allowing a very generous estimate. It would take actually 125 hours before one unit of light was consumed, costing approximately 64d., so that by usine the set four hours a day it would only cost approximately 5}d. a month for B battery supply. Over a period of 18 months the following points are noteed ee

| So that it will be easily seen that after this period the B eliminator has nearly caught up with the expenditure on dry cell batteries, and will_ soot | prove its cheapness as compared with ‘the F batteries. Of course a comparigon of the two as regards volume and freedom from internal noises ig 60 obyiong that it does not require stressing.

: £ s. d. Cost of dry B batteries uw. 9 8 0 Total costs, dry cells ..... 9 9 9 Cost of eliminator ...ccseccereeeeer 910 90 Maintenance of B eliminator for 18 months at four hours ‘otale costs. eliminator........ 919 2