Tips and Jottings

Radio Record, Volume III, Issue 26, 10 January 1930, Page 26

Tips and Jottings

Adjusting Grid Bias. Hu importance of switching a set off before adjusting the grid-bias voltage of any of the valves is not usually realised. While the grid-bias plug is out the valye has absolutely a free grid and the resistance of the valve drops considerably, with the result that the emission increases, and this may, in less time than it takes for you to take the plug out and put into another hole, rise/to a value far in excess of the intended maximum emission of the valve, and thereby do the valve a tremendous lot of damage. All grid-bias plugs should be adjusted with both A and B batteries switched off, ; Uses for Old Files, KEN the worst and most dilapidated of files can often be made use of for doing jobs very different from those for which they ‘were prinarily intended. A half-round tapered file, for example, makes a useful D-bit when its filing days. are-over. The tongue fits quite well into the jaws

of the brace, and used in this way an ancient file will provide a ready means | of enlarging holes drilled in ebonite, One often needs something of the kind. When,. for example, jacks have to be mounted on an ebonite panel, 7-16 inch or #4-inch holes are needed ‘in many.cases. The biggest drill in: the average home constructor’s outfit is the 8-8-inch, which will not, of course, make the holes needed. Put this through first of all, then use an old half-round file in the way suggested, and the job is very quickly accomplished. If you possess an emery wheel you can grind old flat files into useéfil scrapers, whilst round ones may de turned in the same way into cenite punches or nail punches. Preparing Ebonite Panels. PY HEN ‘it is desired to rub. down ebonite panels to produce a.matt surface in lieu of an existing polished surface, many home constructors find that unless extreme care is taken in the operation. the result of using, ‘the usually recommended emery powder, is ° a scratched surface. This effect is naturally not pleasing to the eye, and an improved finish to the work canbe secured if resort is made to the use of "cream grit," This is the material used by monumental masons when rubbing down lead-lettered inscriptions, and. is to be preferred to the usual | emery powder, A Pilot Lamp. N order to reduce the risk of leavs ing a radio set switched on all night, it is advisable to fit a warning lamp to indicate when the filaments are switched on, A _ flash-light bulb,.. having a low-current consumption and | a suitable holder, should be procured and wired directly across the filament terminals of any -convenient valveholder in the receiver. If the set has provision for gramophone reproduction arranged in such a way that the radiofrequency stages are automatically switched off, precautions must be taken to ensure that the lamp is operative when the gramophone pick-up is ‘in use. .