Tips and Jottings

Radio Record, Volume III, Issue 39, 11 April 1930, Page 39

Tips and Jottings

Cleaning Connections. ITH a three-valve receiver of conyéntional type, it is possible for there to be as many as thirty separate plug-and-socket connections. When it is remembered that in radio reception we are dealing with minute currents, particularly on the radio-frequency side, it is easily realised that poor contact in even two or three of these sockets is quite sufficient to materially affect: the sensitivity of the set. Both Plugs and sockets are easily cleaned With smooth emery-paper, and in some cases the iniprovement made will be surprising. In the case of plugs of the split-pin variety, a screwdriver should be forced down the slot so that the two halves of the plug are sprung outwards. A Simple Stain. \ FEW crystals of potassium permanganate dissolved in a cupful of water provide a cheap and simple stain for all kinds of woodwork, and particularly for the purpose of colouring the baseboards and woodwork of pieces of experimental apparatus. Permanganate solutions quickly destrdy thé bristles of brushes, and, therefore, they should be applied to the woodwork by

SSRPSRSSRESSSESSESSELSRSESSSRSSAESSSSECRARS SAREE PES a . means of a piece of flannel. If required, two or three applications of :the stain may be given to the woodwork in .order for it to reach any desired dépth of colour. Permanganate-stained woodwork is eapable of taking a good polish if, after it has been given ample time to dry thoroughly, it is rubbed over with a rag moistened with raw linseed oll, When working with permanganate stains, the fingers invariably acayire a deep brown ahd sometimes an almost black discolouration. This, however, may readily be removed by rub-

bing the hands over with a few crystals of sulphate of soda moistened with a little warm water. Photographers’ "hypo," acidified with vinegar, will also act in the same manner. Tracking Down Howls. SOMETIMES a receiver may suffer from a certain amount of audiofrequency instability which masifests itself in a tendency to produce howling. When‘searching out the cause of this trouble the set owner should bear in mind that this parficular form ofannoyance may sometimes be traced to mechanical vibrations passed from the’ speaker itself to the receiver. Especially is this the case, of course, when the speaker is mountéd on top of the receiver. . . Choosing a B Battery. [THE B battery is generally regarded as one of the chief sources of troubles. In general, the sole reason for this is that as they are in many

cases incapable of supplying the currént requiréd of them, and corisequently they are always overworked arid thus rapidly run down. The correct way to choose a B battery is to ascertain how many milliamps your set is taking in B current, and to choose a battery which is able economically to Stand up to the current drain imposed upon it. If a milliammeter is connect: S ocshatstesantatnteeaneenbasietantemtetedememt eto

ed in the séet’s B lead you can actually measuie the B battery consumption of the set. If it is anything up t6 12 milliamps, the ordinary standard B battery is adequate. If, however, it is more than 12 milliamps when the proper grid bias, etc., has been applied, a double-capacity battery is required, and, of course, if the B. consumption is more than 20 milliamps a double-capac-ity type Will be inadequate, and one of the triple-capatity variefy will be necessary. . 6 0 Cleaning Condensers. UNWANTED noises are. frequently caused in a receiving set by dust collecting on the vanes of the variable

condensers; the’ dust ‘particles provide. minute leakage paths between the fixed and moving vanes. The usual method of cleaning by inserting a feathér between the vanes is not very satisfactory, especially if the condensers . are built up into a set and are in inaccessible positions. A much simpler and more éfficient way of cleaning out the dust is to blow it away with a strong blast of air. A pair of ordinary bellows may be used for this purpose, and indeed for cleaning any part of a set. The bellows should be "worked" a few times before applying the nozzle to the set, to ensure that any dust inside them is blown out.

RADIO ENTHUSIAST HONOURED

QUR short-wave correspondent, Mr. F. W. Sellens, was recently made the recipient of a silver cup presented by short-wave station P.C.J., as a mark of appreciation of the reports which he has been regularly sending in respect of local reception from that station. It is a great honour for a New Zealand amateur to be thus siigled out from listeners all over the world, and we congratulate Mr. Sellens on his splendid achievement. The presentation took place at the monthly meeting of the Wellington branch of the New Zéaland Amateur Radio Transmitters’ Association, held last Thursday evening. Mr, Fitt, who made the presentation, commented on the great service which Mr. Sellens is carrying out in the interests of radio, and added that frequently station PCJ (Holland) made mention of the excellent work which Mr. Sellens is doing.