GB873139A - Telephone subscriber station - Google Patents

Abstract

873,139. Substation circuits. GENERAL TELEPHONE LABORATORIES Inc. Feb. 11, 1958 [March 20, 1957], No. 4447/58. Addition to 858,678. Class 40 (4). A subscriber's subset is provided with pushbutton operated contacts which connect up loud-speaking facilities and disconnect the handset, the push-button being restored to remove the loud-speaker by a linkage associated with the cradle switch when the handset is taken down. The substation circuitry is shown in Figs. 1 and 2 where the receiver and transmitter of the handset are connected in the anti-sidetone circuit of hybrid 20 with switchhook contacts 30 and a calling buzzer 52. The impulse transmitter controls off-normal and impulse contacts 54 to 56. The push-button operated contacts are shown at 40 and divert the line 11 from the handset to a socket 63 which also takes the leads to a loud-speaker 61 housed in a separate cabinet. A plug 64, mating with socket 63, connects line 11 to twostage transistor amplifier 160, 170, for speech outgoing from microphone 101, and to twostage transistor amplifier 180, 190, for incoming speech to loud-speaker 61. The amplifiers are powered from the exchange over a rectifier bridge 70 such that voltages applied to the transistors remain of the same polarity when voltage on the exchange line is reversed. As the bridge 70 always takes D.C. from the line it provides a path for speech currents to and from the hybrid 85. The D.C. supply for the amplifiers is protected from speech by a filter comprised by capacitors 77 and 89 and the coil 75. To adjust the supply in face of varying lengths of exchange line a variable resistor 76 is provided. The microphone 101 is matched to its amplifier by a potentiometer 104 and the volume of the loud-speaker output is controlled by a potentiometer 131. All the components of Fig. 2, with the exception of the microphone 101, are mounted on a plate with the four pin plug 64 so as to be detachably secured to the base of the subset. The exterior casing of the subset carries a grille, behind which the microphone 101 is mounted, and a control knob for the volume control 131, see Fig. 4, not shown. As well as the cradle switch plungers 34, 35, Figs. 6A, 6B, two push-buttons 44 and 45 are provided on the subset. Depression of pushbutton 44 operates the spring set 40 to connect up the loud-speaking system and disconnect the handset and is sufficient to answer a call. Providing the handset is in place the pushbutton 44, once depressed, will stay down, as shown in Fig. 6B, and can be released by depressing button 45 which, by pivoting lever 236, raises button 44 from between the spring-set arms 242. Should button 44 be depressed and the handset be lifted the cradle switch pivot arms 215, 216 move from the positions shown in Fig. 6B to those shown in Fig. 6A, and a spring 254, the portion 261 of which slides in a hole in the end of lever 237, is drawn downwards to engage the lever with a hook 262 and raise the button 44 to connect up the handset.