Found in old documentation, this circuit can use modern equivalent components. The signal has good strength thanks to the use of a power transistor. The Q1 transistor is a unijunction of the time.
This circuit was obtained from an old American documentation, and practically any general-purpose transistor...
This circuit is intended for monitoring an environment. It fires a relay with a sound, but only if...
This circuit is from an old documentation, but perfectly current. In place of the battery, 2 or 4...