Patent GB-847233-A (GB)
Title: Improvements in or relating to telephone call-answering apparatus
IPC: H04M1/65
Filed: 1955-09-19
Abstract: 847,233. Automatic exchange systems. ALLWORTH, S. L., and MURPHY, A. V. Dec. 19, 1956 [Sept. 19, 1955], No. 24028/55. Class 40 (4). After 10-15 seconds of ringing current, answering apparatus closes the loop on line 15, reproduces a message previously recorded on a magnetic drum 90 and records on magnetic tape 115 any message dictated by the calling party. The apparatus is released, with a delay, on receipt of dialling tone or cessation of speech. Control switches Sl to S4 and 6 to 9 enable the recorded message to be reproduced on a loudspeaker or fed to the telephone line. The tape can be stopped or stepped back as required during reproduction. Lamps indicate when the apparatus is switched on, when a message has been recorded, when the tape is broken and when there is insufficient tape supply. General arrangement.-A line 15 is connected in parallel to a conventional set 16 and an alternating current relay A. A speech relay F responds to speech of 600 c/s. or more accepted by a high-pass filter 30, 31. A relay G responds to dialling tone of repetition frequency 33 c/s., Fig. 2, A, and has a guard against speech currents. The operating circuits for relays F, G are described later. The apparatus is switched off, set for receiving a call (R) or set for playing back (P) by means of a three-position switch with three sets of contacts S1 S2, S3, the first two sets controlling the power supply. Buttons 6 to 9 control the magnetic tape 115 and are mechanically interlocked so that the tape run button 6 is automatically tripped if either the stop-button 7 or the rewind button is fully depressed. Operation.-If the switch is set to answer a call (R), relay A responds to ringing current at the same time as the bell rings in set 16. Relay B follows if safety contacts p4, x3, TE1 are all closed. These contacts open respectively when the recording-tape runs, breaks or is in short supply. Relay B locks until tripped by relay H at the end of the call which is signalled either by absence of speech for 10-15 sees., or by dialling tone. The H.T. power pack 12 is energized over contact b2 and motor 13 starts to drive the capstan 95. Condenser 82 charges through resistors 83, 84 and after a delay of 10-15 seconds, valve V1 conducts. Relay C pulls up and falls back again as D follows, locks to H and discharges condenser 82 at d4. Solenoid AN removes a detent 92 from the drum and forces an idler roller 94 between the capstan 95 and the drum. At the same time, the line is looped at d3 to hold the connection and the message picked up from the drum by announcing head 91 is transmitted to the line by amplifier 100 and transformer 22. At the end of the announcement, contact 70 (shown twice) on the drum closes momentarily, relay E pulls up and locks to H. Relay R follows and connects the line through transformer winding 25, attenuation pad 120 and amplifier 100 to the tape recording head. At the end of the message, speech relay F falls back and allows 82 to charge. Relay H pulls up after a delay. Dialling tone operates relay G with the same effect as release of F. Button 6 energizes magnet RP to drive the tape and operates relay P to switch the pick-up head to the input of the amplifier and the loud-speaker 5 to the output. The amplifier output may be connected through transformer 22 to the line 15 by means of a switch S4. Stop-button 7 deenergizes magnet RP to stop the tape drive but does not trip button 6 until pressed to the full. Rewind button 8 de-energizes magnet RP to stop the forward drive and energizes magnet RW to rewind the tape. Button 6 is tripped if button 8 is fully pressed. Button 9 de-energizes the magnet RP and energizes the fast drive magnet FF. Speech relay F.-Relay F operates in the anode circuit of pentode V3 when speech signals of over 600 c/s. are accepted by a high-pass filter comprising resistor 31 and condenser 30. Triode V2, which acts as a limiter, is normally conducting and is driven to cut-off by grid current on receipt of a signal. Half-cycles of speech current are repeated as pulses of uniform intensity. Triode V2 is transformer-coupled to pentode V3. Transformer 39 and rectifier 41 provide positive feed-back to speed-up operation. Dialling tone relay G.-Relay G is normally operated and is released by dialling tone. Pentodes V5, V6 are coupled by a full-wave rectifying circuit and the time constant of potentiometer 54 and capacitor 53 favours the 33 c/s. dialling tone repetition frequency and its lower harmonics. A further resistor 55 and a capacitor 58 link the potentiometer with the grid of V6. The potentiometer is adjusted so that only the tips of the dialling tone pulses drive the pentode V6 into cut-off to repeat the tone as positive pulses at the anode of V6. The syllabic speech pulses drive the pentode V6 well into cut-off and no signal passes V6. Pulses developed across circuits 62, 63 tuned to the dialling tone repetition frequency 33 c/s. or one of its harmonics are fed to a full-wave rectifier circuit 65 which in about 2 seconds builds up a sufficiently negative potential on condenser 68 to cut off V4. The contact g1 may be connected in series with h1 so that dialling tone releases the circuit without delay. Relay D may be substituted for C in the anode circuit of V1 providing self-holding contact dl comes up before d5.