Moving Coil Speaker Operation

Radio Record, Volume III, Issue 36, 21 March 1930, Page 31

Moving Coil Speaker Operation

Overloading Rectifiers ANY moving-coil speaker users energise the field from a battery charger which includes a dry rectifier. The output of such a device is, of course, unsmoothed, but the heavy inductance of the field windings is generally sufficient to provide practically all the smoothing required. ‘In some eases, however, and particularly with moving-coil speakers which really go down below 100 cycles, there is still sufficient hum to be annoying, and it has been discovered that this hum can be removed completely by connecting one of the very higheapacity electrolytic condensers across the field windings. What is not generally known is that the presence of such a condenser greatly increases the load upon the rectifier, and may in some cases seriously overload it. Take, for example, the case of a loudspeaker which, when connected to a dry rectifier, giving six or seven volts output, takes just under an ampere, which is not too much for the particular rectifier. , The connection of an electrolytic condenser across the winding will mean that the rectifier is called upon to give not only the one-ampere field winding, but a very considerable additional current, which will flow into the electrolytic condenser at each puisation. In such citeumstances the load on the rectifier may rise considerably above one amperé, and this point should be carefully watched by those who are running dry rectifiers near to their safe limita,