We found this precision circuit in a manual from the 80's. The operational amplifier is of a common type at the time, and equivalents can be tested. Transistors are general purpose types.
We found this circuit in an English documentation from the 60s. The integrated circuits are the...
This circuit was found in a 90s Popular Electronics. It generates tones given by the oscillators and...
This amplifier circuit applies its signal to an ordinary audio amplifier to pick up signals from a...