GB696885A - Improvements in telephone systems including loud-speaking equipment - Google Patents

Abstract

696,885. Direct call systems; loud-speaker systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Nov. 22, 1950 [Dec. 2, 1949], No. 30986/49. Class 40 (iv). In a telephone system including a loudspeaker substation incorporating an amplifier, a suitable balancing network is connected across the amplifier line terminals whilst a connection is being established, and at any period during which the amplifier is energized and the other party disconnected. In a P.A.X. system, a loud-speaking master station MS, Fig. 1, is able to set up a direct call over a key calling relay set KCRS to any one of a selected group of subscribers on the P.A.X. A power key (not shown) connects the amplifier power supply, disconnects the buzzer and completes a loop across the line. The master station then throws a key KL appropriate to the wanted subscriber which operates a relay SW to busy the master's P wire, start a ringing vibrator and operate relays L and SR. Contacts of the relays L and SR together complete a circuit for a supervisory lamp LP and the relay SR energizes relay H and removes the shunt from the left-hand winding of a relay PT which operates over contacts of relay H if the called party is free. The wanted subscriber is then called over contacts of relay SR which has been released by relay PT, and ringing tone is sent to the master. The release of relay SR also extinguishes the lamp LP. The called party in answering operates a relay F which releases slowly the relay PT and in consequence re-energizes the relay SR to disconnect the calling signal and ringing tone. The relay SR also completes the talking circuit over lines LC and removes a temporary balancing network comprising resistance YC and condenser QC from across the calling line. The master station may dial a further subscriber over the P.A.X. proper whilst still holding the originally called station by throwing a holding key KH which releases the relays SW and L, causing the connection of the master station to the exchange, re-connects the temporary balance YC and QC across the line of the called subscriber and lights lamp LP. If at the conclusion of the original call the called subscriber clears first, then the temporary balance is reinserted by relay SR. The master is also able to break in to an engaged subscriber and request that one of them hangs up so that his call may be established. A temporary balance connected across the input to a final selector and under the control of the A relay is described with reference to Fig. 2 (not shown). Specification 628,008 is referred to.