We found this circuit in a 1967 American documentation. The diodes are general-purpose and the input frequency can be between 80 and 800 Hz.
This circuit was found in an American documentation for radio amateurs of the 80's. The...
Found in a Philips documentation from 1968, this circuit detects the trimpot set input voltage....
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...