DANGER TO LOUDSPEAKER

Radio Record, Volume I, Issue 7, 2 September 1927, Unnumbered Page

DANGER TO LOUDSPEAKER

OVER 110 VOLTS RISKY. Radio dealers in New Zealand sometimes have loudspeakers Lrought to them with the wiring of the coils burnt out This is caused by using too high a plate voltage (from the B battery) without connecting a siftron or. other choke and condenser device, or transformer, between the loudspeaker and the set when more than 110 volts is fed from the B battery. ,

Ever since the advent of the power valves of the 112 and 171 type for use in the last stage of audio-frequeney amplifiers, there is an attendant danger that some damage may be done to the windings of the loudspeaker, unless some protective device be inserted in the ontpnt circuit of the nower tube. The plate voltage required by these tubes is anywhere from 135 to 180, and, in the majority of cases, such a voltage flowing through the loudspeaker windings will burn them ont, or cause some other damage. | The protective device imentioned above generally takes the form of either a 1:l-ratio transformer or an audio-fre-quency choke coil, with a large fixed condenser placed in the plate lead of the power tube. By cither of these means the high voltage is supplied to the plate of the tube without passing through the loudspeaker coils.