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The output telephone signal is more powerful then the signal fed to base of the transistor T 1 . The output signal from transistor T 1 is fed to pin no 3 of power amplifier LM386 which amplify up to necessity level and output is obtained from pin no 5 is fed to speaker through capacitor C 9 . The V CC is given to IC 1 through pin 6. The telephone signal is fed in to circuit through two ways. Direct supply telephone signal from telephone line to the point where coil L 1 is connected as shown in figure 2. Or connect this peak up coil L 1 and so adjusted near telephone set where excellent voice be able to single out.  Simple Telephone Amplifier Circuit Diagram PARTS LIST Resistors (all ¼-watt, ± 5% Carbon) R 1 = 100 KΩ R 2 = 39 KΩ R 3 = 2.2 KΩ R 4 = 680 Ω R 5 = 100 Ω VR 1 = 4.7 KΩ VR 2 = 10 KΩ Capacitors C 1 = 27 KPF (273) C 2 , C 4 = 2.2 µF/16 V C 3 = 22 µF/16 V C 5 , C 10 = 100 µF/16 V C 6 = 10 µF/16 V C 7 = 100 KPF (104) C 8 = 47 KPF (473) C 9 = 220 µF/16 V Semicond...

This circuit will illuminate a LED if one of your telephones is in use. It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC. Please note that it is illegal to make a physical permanent connection to your telephone line in some countries (this includes the UK and Ireland). If building this circuit it is advisable to use a plugin cord so that the unit can be unplugged should a fault occur. If in doubt consult either your telephone or cable operator. If all extension phones are on-hook and the line voltage is around 48 V, Q1 will conduct thus effectively shorting the gate of Q2 to its source, so it will be off and the LED will be disabled. Lifting the handset of any phone on the line causes the line voltage to drop to 5-15 V. The gate voltage of Q1, equal to some 6% of the line voltage, will then be too low and Q1 will be turned off. So Q2's gate is now biased at approximately 1/2 of the line voltage, Q2 turns on and the LED indicate...

This is a Simple Telephone In Use Indicator Circuit Diagram . With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause the FET (2N4360) to turn on and also turn on the transistor (2N2222). When the transistor turns on it will allow current to flow through the LED and make it light. A blinking LED could be used to make the effect better.  Simple Telephone In Use Indicator Circuit Diagram