Patent GB-490825-A (GB)
Title: Improvements in and relating to sound recording and reproducing apparatus, applicable to telephone systems
IPC: H04M1/65
Filed: 1937-02-18
Abstract: 490,825. Substation equipment. SOUKUP, J., ZERNER, F., HOLMES, A., and WARMAN, W. H. Feb. 18, 1937, No. 5013 /38. Divided application. [Class 40 (iv)] In equipment for recording and reproducing messages received during the absence of a subscriber, the substation loop includes the recording and reproducing instrument and auxiliary devices such as a reply pick up and signalling device some or all of which are normally short-circuited over contacts opened in turn by a shaft driven by the motor. The exchange line A, B is switched from the telephone set Y to the recording &c. equipment by contacts Ur1 operated by a control handle which also closes other pairs of contacts or, the left-hand pair of a set of three all bearing the designation U. The current supply circuit N, rectifier 22 and control relays HA, Z, for the motor M and amplifier W form no part of the present invention. The arrival of a call operates H which starts the motor, and when normal speed is attained, governor or the like G closes contacts G1. After a predetermined number of revolutions, contacts M2 close to trip the exchange circuits followed at appropriate periods by the opening of contacts M3 shunting a reply pick-up Q, M4 shunting a syren S, signalling microphone or other device giving an audio frequency signal, and M5 shunting the input circuit F, C, P. of the recording and reproducing amplifier. Contacts M5 may be omitted. The signalling device indicates the state of preparation of the equipment and gives time for the amplifier valves to heat up. The meaning of the signals, which may also occur during recording, may be explained by the reply record, or another pick-up and record may be used. Instead of a siren, the blades of a fan for removing record shavings may be used to induce audio-frequency currents in the line and if the speed is too high some of the fan blades may be magnetic and others not. The switches 7U-10U control the connections to the input and output of the amplifier of the combined recording and reproducing instrument D. The line input is controlled by potentiometer P and the instrument D is controlled by potentiometer R, potentiometers being also used if required to control Q and S. The amplifier may have automatic volume control. When the recording period terminates, contacts M2 open the substation loop. When the subscriber returns, he moves the control handle U to the intermediate position in which the telephone set is re-connected to line. The other U contacts may also be changed over or the handle may require to be moved fully to change the connections of amplifier W to the instrument D and loud-speaker T. By suitable modification of the switches, reproduction without amplification may be heard in an ordinary receiver If the calling party does not hold the line until the motor circuit is opened after the recording period, e.g. if he does not want to record, a circuit G2, M2a, l, Fig. 1 (Comp.), controlled by a line relay L and motor controlled contacts closes, on relapse of L, a busy signal circuit from ground E to one of the exchange lines.