The magazine tells about the amps that make the sound in the handset louder ("Radio", 1996, No. 6, p. 36). Described below is another such an amplifier, which is used in industrial telephones.
The amplifier circuit shown in Fig. 1. It is powered directly from the chains phone and doesn't have an output transformer, which made the device is small-sized.
Variable resistor R1 to adjust the volume. Instead, you can install constant at the same value, and parallel to it to mount the toggle switch. When the closed contacts of switch the gain is at maximum.
The amplifier is applicable to any transistor series MP structure R-n-R. Permanent resistors - MLT-0,125, alternating from small receiver. The Capacitor C1 - K50-3, C2 - C50-6.
Details of the amplifier are mounted on a printed circuit Board from folgirovannaya fiberglass (Fig. 2), which is placed directly in the phone the handset. The capacitor C2 is mounted on the Board in the lying position.
Author: L. Poroshenko, Chistopol, Tatarstan