We found this circuit in a 1980s documentation. Equivalent components can be used. The circuit senses temperatures in the range of 0 to 50º C and uses a transistor as sensor.
This audio stage can be used in siren circuits, sound effects and others to excite a few watts...
In the figure we have the way to make the connection of voltage regulators in series to obtain a...
This circuit was found in a 1967 US documentation. The FET is general purpose and the 6V zener....