Leak Detector (CB22456E)

We found this circuit in a Popular Electronics from 1992. The transistor is general purpose, assuming equivalent.

Logical Probe (CB5908E)
The transistors of this circuit may be general purpose and the power supply comes from the TTL...
Audible TTL Probe (CB5907E)
This circuit was found in a 1980s documentation. The IC is the 7400 and should be powered with 5...
Electronic Machine Gun (CB17369E)
Touching the sensor with your fingers, this circuit produces a machine gun sound. The circuit must...