Tips and Jottings

Radio Record, Volume III, Issue 16, 1 November 1929, Page 29

Tips and Jottings

To Cure Distortion. MILLIAMMETER is invluable to all those whose aim it is to secure distortionless reproduction. The meter is inserted .in circuit between the "B--" lead to the last valve, and the loudspeaker or choke terminal to which this lead goes. The object is to attain an adjustment of signal strength which does not produce needle "kicks." It is usual to permit not more than a variation of 10 per cent. of the anode currént in the form of "kicks," and if the ‘needle fluctuates more than this amount the B battery and grid bias supply should be increased. Another remedy is to insert. a more suitable ‘power valve in the last stage. A suitable milliammeter for most purposes is one having a reading of 0-25 milliamps.

‘High-frequency Chokes. ITH the application of more modern forms of tuning, many constructors probably have in their workshops a collection of discarded plug-in coils and sockets. These are quite suitable for use as high-frequency chokes, and can ‘be used for short-wave purposes, as well as for the broadcast band. For the medium broadcast band, a 250 or 300-turn coil is adequate, while for usé on the higher frequencies, a 60 or 70-turn coil is quite large enough. Aerial Coupling. DP2BAD spots (ie, frequencies at which the receiver does not oscillate) in short wave reception are generally due to over-tight aerial coupling. A very small-series condenser or a detuning coil in series with the aerial (50 turns on a 8-in. former is ample) will usually cure the trouble. In some eases, however, the trouble. may be caused by a circuit. which happens to be tuned to a frequency within the range of the receiver, though situated two or three feet away. Metal-Working. WHEN drilling holes in thin sheetmetal constructors will no doubt have. noticed that it is not an easy matter to ensure the drilling of a good clean hole. This is primarily due to the fact that the drill bites the metal when just on the point of emerging. The diffieulty is best-overcome by backing the thin sheet of metal against a piece of hard wood, or, better still, a thicker sheet of metal, The sheet. must be tightly clamped to the backing. material, otherwise no real benefit will result. To Clean Terminals, NYONE who has dismantled an old receiver in order to use the parts for a more modern set will have met with the difficulty, of removing nuts from terminal shanks to which connections have been soldered. A certain amount of solder usually remains in the end threads of a terminal shank when the connecting wire has been pulled off, so that the nut becomes fixed so tightly when an attempt is made to unscrew it that it has even-' tually to be cut off, A die of the correct size for the terminal shank is invaluable on such occasions. With its aid the thread of the shank may be cleaned up in a few moments, making the removal of the nut a simple matter, and leaving the terminal as good as new. . ‘ or 4