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Radio Record, Volume I, Issue 7, 2 September 1927, Page 14

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Constructors who are about to make a low-loss coil for a erystal set should read the instructions for making such appearing under the Browning-Drake heading in this page. "Megohm" thanks those readers who have sent in suggestions for subjects to be dealt with in this columu. These suggestions give a good indation of {he items most required, and of course, the same requirements have been mentioned by several, but those who have written are assured that practicaly everything asked for is noted for treatniefit in due course. Several useful ideas are now under experiment for description as soon as completed.

A number of inquiries regarding details in the construction of the 112-yolt B accumulator have been answered by post. After the first few charges the current may he strengthened considerably without doing any harm. Recent experiment shows’ that it takes about three weeks’ daily charging before the lead plates begin to hold their charge for twenty-four hours, During the first week no useful work must be expected, and during the second and third weeks a charge must be given immediately ‘before use, but may only fast two or three hours. After three weeks the improvement is rapid, especially with frequent and regular use. his forming is a little tedious, but well repaid in the end, as the battery will stand ‘sporting’? without harm, and will give long service without even tenewal of the acid.

A number of correspondents have written asking where they can procure sundry supplies. A much-needed article for constructors is an cighth-incli threaded brass bolt half-inch long, with countersunk head and hexagonal nuts to fit. ‘These can be purchased from Messrs. B. W. Mills and Co., Ltd., Jervois Quay, Wellington ‘The bolts are as. and the nuts Is. Yd. per gross. Brass washers, the smallest with 3-16th -ineh hole are supplied by the same firns

at 2s. 8d. a gross. Messrs. Geo. W. Wilton and Co., of Upper Willis Street, Wellington, supply test tubes, chemicals, and pure aluminium sheet. This information is for the benefit of country readers who are sometimes in a diffiwulty to know where to procure supplies. By courtesy of Messrs. John Chambers and Son, Ltd., of Cable Street, Wellington, "Megohm’’ has tested one of the Carborundum Comipany’s car borundum crystal units with battery and potentiometer. In operation there is a fairly critical position of the potentiometer at which greater clarity and an increase in volume are noticed. ‘his fact makes the unit very suitable tor amplification in any way, either as detector in a multi-valve set, or as the crystal in a reflex set, where the finding of a suitable crystal sometimes constitutes the most difficult part of the work. Used without the stabilising unit, the crystal alone is excellent, givwg smooth tone and good volume with coutinuous reliability, as it requires no setting and there is no adjustment to fiddle with. The price of the crystal alone is 7s. 6d. and the complete stabilising unit 17s. 6d. This firm also stocks a carborundum resister (2s. each) in 50,000 and 10,000 ohms, with noiseless action, which proved very suitable when used in the detector circuit of a B eliminator. :