GB1257776A - - Google Patents

Abstract

1,257,776. Substation equipment. GENERAL ELECTRIC CO. Ltd. 3 Feb., 1969 [3 Nov., 1967; 19 July, 1968], Nos. 50120/67 and 34571/68. Headings H4J, H4K and H4X. [Also in Division G5] A tone sounder for use in place of the bell of a subscriber's set comprises a pair of acoustically and electrically coupled transducers which are caused to "sing" when ringing current is applied thereto. The microphone is of the carbon type so that during each half cycle of ringing its polarity of energization is changed whereby the resonant frequency of the coupled transducers alters, e.g. from 1200 to 1800 c.p.s. The transducers may be the normal microphone and receiver of the set (Fig. 1, not shown), an additional carbon microphone coupled to the normal receiver (Fig. 2, not shown) or an additional receiver coupled to the normal microphone (Fig. 3, not shown). In Fig. 4, both transducers 21, 22 are additional to the normal ones. Thermistor 9 prevents "tinkling" due to line noise and, when the handset is on-hook, prevents speech signals in the vicinity of the set from being sent to line, i.e. an anti-bugging device. The sounder may be coupled to line by a transformer (not shown). Incoming speech signals may be applied to a transistor amplifier (not shown). Transducer assembly (Fig. 5). A plastics moulding 42 in the form of two shallow, roundended boxes interconnected by a slot 46, has a carbon microphone 44 and a rocking-armature receiver 45 mounted in apertures in two of its major faces. The volume of sound emitted by the assembly may be adjusted by varying the area of holes 48 with the aid of a shutter (not shown). The assembly is a direct replacement for the conventional bell and the lower face "48" is secured to the base of the set.