This audio oscillator is from a 1957 Raytheon publication. The tone generated depends on C2 and C2 and the handset must be high-impedance magnetic. Equivalent transistors can be tested.
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
This monostable circuit, from a 1977 Radio Shack documentation, uses a 7400. The time is given by the...
The circuit shown in the figure activates a small indicator lamp that will start to flash when the...