HEADPHONE RATTLE

Radio Record, Volume I, Issue 34, 9 March 1928, Page 3

HEADPHONE RATTLE

A SINGLE CURK. Que earpiece in a pair of head telephones can easily get out of adjustment without the owner realising that it is faulty. his happens through the metal digphragm just ruder the ear cap, touching the magnet polepiece inside the cap, instead of being just clear of it. he sound from the recciver is produced by the vibration of the diaphragm, and if it touches the magnet it cannot vibrate freely, and the sound it produces is much reduced. If only one headphone is faulty the trouble is ofte’ not noticed, or if it. is the decrease in signal strength is blamed on to the broadcasting station. ‘The headphones can easily be tested. If the portion of the diaphregm visible through the hele in thie centre of the earpiece is lightly tmapcd ith the fingernail or a pencil end, a faulty earpiece will give ont a dead, metallic sound. If the adjustment is correct a characteristic hollow noise is produced by tapping the diaphragm. Much care should be taken to see that the diaphragm is not struck hard cnough to dent it. A faulty telephone can Ie readjusted often either by screw- ing the cap slightly tighter or loosening it a little. If this fails the cap should be removei and the diaphragm carefully lifted off the body of the earpiece. A light paper ring can then be cut to fit between the body of the receiver and the diaphragm. ‘The presence of this ring between the receiver and the diaphragh will hold the diaphragm clear of the magnet poles. ‘The Aiaphragm cati also be reversed, and if it is slightly bent the diaphragm will not touch the magnet.

Scientists have discovered that a piece of metal cooled to extremely low temperatures beconies almost a perfect conductor. An English experimenter, Mr. Ajan J. Bremner, has announced to his radio society that when tlhe antenna coil of a set is immersed in liquid air, while the strength of the signal is not increased, the selectivity becomes remarkably high.

A flash lamp bulb connected in the negative lead of the "B" battery makes a very good fuse. Should the battery become short circuited, the lamp will * burn cut, thus breaking the circnit, and the battery will Le saved.