To Prevent Noise

Radio Record, Volume III, Issue 12, 4 October 1929, Page 31

To Prevent Noise

S$ a rule it is usudl to employ a variable condenser on the short waves for controlling reaction. It is impossible to keep such a condenser completely free from dust, and any small particles which become lodged between the two sets of plates will cause a crackle and scraping noise as the condenser spindle is turned. This trouble may be removed by inserting a fixed condenser in series with the variable one. The value of this fixed condenser may be in the neighboyrhood of .001, although a much smaller one can ‘be employed if the variable reaction condenser is found to be too large. Incidentally, such a condenser acts a8 a safeguard for the valves in the event of thé variable céndenser becoming shorted, in which case it is possible for valves to be burnt out.