This low frequency oscillator circuit was found in an Electronic Design from the 90s. The transistors are common types, and the frequency is given by the crystal.
The operational amplifier for this circuit found in a 1979 documentation may be the 741. We can...
The UM3562 integrated circuit (not very easy to find) synthesizes three types of sound that...
This stethoscope or amplifier for hearing aid using a crystal headset and microphone was found in a...