Tips and Jottings

Radio Record, Volume III, Issue 54, 25 July 1930, Page 29

Tips and Jottings

Detecting Distortion. N excellent test for the detection of distortion is to connect a milliatmmeter in series with the plate of the output valve. The needle should remain comparatively steady, the maximim permissible variation on either side of the mean being about 10 per cent, If the needle is constantly kicking toward the right it is probable that the grid bias: is too high for the amount of "B" battery current used. The bias voltage should be adjusted from time to time as the "B" voltage drops. Should the needle kick toward the left, more grid bias voltage should be applied. When Using Small Drills. QMALL drills very often cause a good deal of annoyance to the radio constructor, for many of them obstinately refuse to be gripped adequately by the chuck of the brace. In such instances the usual practice is to bind paper round the drill, ot else to pack some material or other into the jaws of the chuck. A better method for enabling a small drill to be gripped

securely by the brace is to wrap several turis of insulated wire round the end of the drill Home-made Screens. OME set builders dislike the construction of metal screens owing to the necessity of cutting fairly thick copper or aluminium sheet. A certain amount of skill in metal work is also required to make a neat turnover at the bottom of the screen without the aid of proper forming tools. A simple plan is to make a screen former from three-ply wood, and to cover it ‘with copper .or aluminium foil, which may be easily cut with Rivets may be used to attach the metal to the plywood, and small bolts passed through the top of the screen will enable connections to be made to it. If desired, bare wires may be passed through the screen without fear of "shorts." This is accomplished by drilling smail holes in the wooden part of the screen and large ones in the foil. One marked advantage of this method of screen construction is that no difficulty will be experienced in making. soldered connections, because the metal is a good deal thinner than that usually employed for screens. °