This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. 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...