Telephone concentrators as well as old industrial telephone hub type KD-6 and COP-6 does not have a loud call, and therefore, when use them in areas with high noise levels, the call might not be heard. I added your hub, as well as many CD-6, unit call from a standard phone call, which is included instead of the cap the acoustic signal.
The principle of operation of the device is schematically shown in the figure, is next. When a call is received at its input transistor opens. Positive impetus to the collector circuit of the transistor opens the thyristor COOK, and the call starts. Other details form simple parametric the stabilizer.
To call and power transistor is used alternating current from a separate step-down transformer. Because the thyristor enters non-sinusoidal voltage, the call should be installed in a vertical position. The polarity his inclusion is determined empirically.
Transistor MPB can be replaced by NB. The thyristor can be replaced by KUN. The R2 resistor wire.
Author: A. White, Donetsk region, Artemovsk