This two-transistor circuit consists of a powerful industrial-use siren. The circuit is from a Radio Electronics from November 1963. The powerful power supply is included.
This circuit is from 1957 Raytheon documentation. The phone must be high impedance with 600 ohms...
This circuit can be applied to several logics. The circuit is from an Electronics Now from the...
This circuit was obtained from an American publication of 1982, but can be assembled with ease...