Laboratory Jottings

Radio Record, Volume II, Issue 49, 21 June 1929, Page 31

Laboratory Jottings

~ Cossor Melody Maker, P.R. Steel Masts The Well-mayde Trickle Charger

he Agen Well-known Trickle Charger. VTHE Well-mayde trickle charger (Johns Ltd.) has been tested and has been found to give perfect satisfaction. The charger is substantially constructed and encased in metal, its dimensions being about Sin. x 4in. x 4in. Voltage taps at 6, 4 and 2 are provided, so that any type of "A" battery may be charged. Rectification is accomplished by the British Westinghouse units-a metallic rectifier having the distinct advantage that it will not give trouble by burning out, nor does it require constant attention, as does an _ electrolytic. Thus, perfectly silent rectification results. Although while under official test the charger was left charging during very long periods, "here was absolutely no sign of heatthe top of the charger becoming not even becoming slightly warm at the end. The charging rate is stipulated at 3 ampere, It was found that it is slightly above this, approximately .55 amperes, This renders it suitable for certain types of dynamic cone speakers which require 4 ampere to energise the field coil. When not charging a battery it was connected to such a speaker and gave perfectly satisfactory results, there being only a very slight hum in the speaker. This can be explained by the fact that the speaker required .65 amperes and the charger supplied .55.. This hum, however, was not sufficient to be distracting. It was found that the charger would operate for about 85 hours on a unit of electricity, which, in the Wellington district, costs 2d. This means that it can be operated at a cost of less han a thirtieth of a penny per hour. PR Light Steel Masts. "THE light steel masts supplied by the Domestic Vacuum and Radio Company, Limited, Auckland, should appeal widely to listeners who require a light but substantial mast. These Hnglish masts are obtainable in 34ft. and 42ft. sizes, built up of sevéral lengths of light steel which slip into one another in a telescopic fashion; each tube is secured to the next by a_ bolt. This is preferable to a serewed mast, as threads are liable to weaket the join. At each join, that is, at approximately each 7ft., a steel ring allows of connec-

tion of guy wires. These are supplied with the masts already cut to size. Assembling the parts is quite a simple task, and if the instructions are followed no difficulty will be encountered in erecting. Having erected a pair of the 42ft. masts ourselves, a few points of special interest have arisen. With the New Zealand climate, it is absolutely essential that the guy wires be taken out to at least 9ft. from the mast. Where conditions are very trying, such as in Wellington, the guys could be carried to a much greater distance with advantage. By staying out the guys to ‘this length, the masts will stand up to the severest atmospheric conditions, Already the masts in question have weathered without the slightest signs of moving several of Wellington’s severe gales, so that it can be claimed that under these conditions they give every satisfaction. On- properly tightening the stays, it was found impossible to move the masts, even when in a heavy gale. They are certainly very neat and businesslike in appearance, and as a good aerial is worth an extra valve, it can be claimed that good,. high masts such as these are really worth while. If the halyard supporting the aerial is of stranded wire, a pulley with less play than those provided will have to be used. Those supplied are intended for special tarred rope which forms an excellent halyard. The Cossor Melody Maker. DURING the last week we have had the opportunity of testing the "Cossor Melody Maker’ supplied by Radio Ltd., Auckland, who are the North Island distributors for Cossor products, _ This 3-valve set has given very fine results both as regards tone and volume. The circuit is a slight adaptation from the normal regéneriative.

but is, generally speaking, straight-out. The screén grid valve for radio frequency is shielded by a screen between it and the remainder of the circuit. The whole is shielded by a metal case, and this is finished in a dark brown enamel which gives a very pleasing appearance. The coils plug iito valve sockets. Regeneration is controlled by a midget variable condenser, which is particularly smooth in its operation. There are ‘two tuning dials controlling the condensers tuning the radio frequency and the détector coils. Two other controls remain on the panel, the filament switch, and the adjustable rheostat for thé filaments. The valve combination is good, and sufficient volume to listen to in comfort can be delivered at will from a local station without distortion. This, however, can be very easily controlled by the filament rheostat. During our test, this method was resorted to in controlling the output from 2YA without detriment to the quality, which was excellent. The voltages recommended are: B+1 (screening grid) 80 volts, B+2 (valve plates), 135 volts, grid bias 9 volts, 4s provided by a small battery which fits inside the cabinet. The most outstanding features of the test have been 1YA, 8YA, at. good strength daylight reception, and three Japanese at full speaker strength. The two New Zealand stations received during the daytime were brought in while Wellington was operating; but a wave trap was used, It was found by the use of this small attachment these two stations could be relied on during the early evening, and later 2BL, while yet Wellington was operating. Under these conditions, it was found possible to log very many of the Australian stations. The full log of stations received at speaker strength is as follows: 1YA, 2YA, SYA, 4YA, 2YB, 2Z¥F, 2BL, 2FC, 2UB,. 2KY, 2GB, LO, 8UZ, 3AR, 4QG, 5CL, JOFK, JOGK, JOHK. A very interesting evening was spent with the Japanese. On this occasion it was possible to tune-in all thtee on the dynamic speaker. So clear and distinct were the signals that they could be heard plainly in 4 room some 25 yards from the speaker. Actually the five high-powered stations were received, but thesé only loud enough to hear éasily. The aerial and earth used in conjunction with this test: weré very good, comprising an aerial 40ft. high, and om an

120ft. long, and a Pearce earth system. The laboratory is situated some four miles airline from 2YA. The voltages used were those recommended. Two speakers were tried out, an ordinary cheap cone, and a dynamic cone. All the stations logged could be received well on this latter speaker.