Phone amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony
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This amplifier is designed for those who are hard of hearing, it is effective even when the signal on the line is weakened for some reason.
The amplifier is mounted on a board measuring 20 x 25 mm and placed in the handset under the telephone capsule, if the device is of the old type, or in the middle of the handset, if the device is of the TA 11320, TA11322, etc. type. The outputs of the amplifier circuit, marked with the corresponding color, are connected to the contacts on the microphone holder. As VD1 - VD4, diodes of the type KD102, D226, D223 can be used.
Instead of VT1, you can use transistors MP40A, MP26, capacitor C1 - type KM, resistor R2 can be both variable and constant. The value of the latter is selected by the disappearance of the acoustic connection between the microphone and the phone.
Author: L.Ponilov; Publication: N. Bolshakov, rf.atnn.ru
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