Notes of Interest

Radio Record, Volume II, Issue 36, 22 March 1929, Page 31

Notes of Interest

The Importance of Good Contact. Too much stress cannot be laid upon the importance of good contact, and, as with the crystal set every iota of energy must be utilised, the importance of good contact is paramount. When strong signals are received on a powerful receiver, it is possible that quite a deal of current be lost through bad contact, and yet the station be received at quite pleasant volume. However, with the crystal, the-case is altogether different, for if any energy is lost the signals become painfully weak. All the wires should be securely attached to terminals and, in cases where there are no terminals, solder should be applied. A case was recently brought before the writer clearly examplifying this point of good contact. The receiver in question was causing a great deal of crackling noise in the ‘phones, and the signals were very weak. On examination it was found that of the three terminals two were loose, and one joint was most insecure. Another fault in this receiver that was causing very much trouble was that the ’phone tips had broken off, and the wire nearly twisted round the terminal, with the result that every movement of the listener caused a crackling noise.

Where a sliding contact has to be made, both sides of the contact should be perfectly clean. If the slider is operating on a coil the surface should be touched up occasionally with emery paper. Fixing New Telephone Tips. AFTER a little use, the tips of the telephone cord may break away, or become so damaged that a very bad contact is made, and it thus becomes necessary to replace them. ‘This is quite a simple job, and can be done without a soldiering iron, and yet make a very firm contact. If the tips are still available, they may be used, otherwise new ones will have to be purchased. Clean the wire thoroughly for a distance of about one inch. Now. heat the tips in the flame of a candle, or in a hotter flame if available (gas, for example). A red heat is unneces~sary, and may cause great damage. When properly hot the solder already in the clips, if they are old, will come away bringing with it the remainder of the old ’phone coil connection. Now take a roll of resin for solder, and with a pair of pliers cut off about half an inch or a little more. This will just go inside the ’phone clip. Heat this over a flame until it becomes molten. When in this state insert the clean cord tip, and, when cool, bind the end of the insulation with cotton to keep it from further fraying. A little insulation tape now wound around the connection between the cord and the tip will give added strength and durability. Crystal Breaks Down. AN interesting case in which the breakdown of a permanent crystal caused some deal of doubt as to the origin of weak signals has been very recently brought to the notice of the writer. For some considerable time, the strength of signals had been falling off, and everything was blamed, from loose connections to the local station, but all were perfectly innocent. The tuning, too, was very flat, and very little difference was noticed between any two positions of the condenser. Finally the crystal was suspected, and a simple test revealed this to be the case. One end of the crystal was attached to a battery of 22 volts, and the other end to one tip of the télephones. The other tip of the telephones was connected to the end of the battery and a loud click was the result, showing that current was being passed in that direction. On the reversal of the erystal an equally loud click was heard, which showed that current was being passed in the opposite direction, showing that the crystal, passing current in both directions, was not rectifying. 7 English Carborundums. N the past all carborundum crystals have been manufactured in America, but an English firm has now commenced their manufacture and these are now on the New Zealand market. They are proving equally as good as the American crystal, and certainly nothing could be finer for the listener who desires loud sgnals with a minimum of trouble.