GB492368A - Improvements in or relating to telephone amplifiers - Google Patents

Abstract

492,368. Substation equipment. HUTTER, E. JONTOF-. Dec. 15, 1936, Nos. 33897/36, 10671/37, and 19862/37. [Class 40 (iv)] An amplifier and loud-speaker are fed with speech from an ordinary telephone receiver by means of a coupling device comprising a speech coil carried by a permanent or energized magnet with a gap adjacent the diaphragm of the receiver. The device may also be used to transfer to the receiver, speech from the loudspeaker operating as a microphone, or a separate device may be used for outgoing speech. A single amplifier may be used for both directions and manual or automatic switching means may be provided to control the connections to the input and. output of the amplifier. The telephone receiver 15 is placed on a stand against a perforated plate 12 covering a casing containing the coupling magnet 16 and speech coil 17 which may be connected to a manual volume control 18 in the base of the stand. In the automatic switching arrangement shown in Fig. 3, the combined loudspeaker and microphone 21 is normally connected over transformers 31, 33 to the input of the amplifier 20, the output transformer 36 being connected to the coupling device 19 which, however, is normally open-circuited at relay contacts B controlled by winding 44. On speaking into instrument 21, the output of the amplifier is applied to valve 43 energizing the winding 44 so that contacts B complete the circuit of the coupling device 19 and disable a valve 46 which by means of winding 47 controls relay contacts A. When incoming signals are applied to the coupling device 19, valve 46 energizes winding 47 so that contacts A disconnect transformers 31, 33, connect the coupling device to input transformer 33, and connect output transformer 36 to the transformer of instrument 21 which now operates as a loud-speaker. Automatic volume control may be provided, and additional dual-purpose instruments 21 or separate microphones and loud-speakers may be located in different rooms and connected up selectively by a switch. Specification 343,625 is referred to. The Provisional Specifications also describe the use of a microphone, an ordinary receiver or a moving coil instrument for picking up signals from the telephone receiver ; the use of separate amplifiers for the two directions of transmission; and the application of the amplifying arrangements to the telephone receiver of a crystal wireless set. Reference has been directed by the Comptroller to U.S.A. Specification 1,842,190.