Found in an American documentation from 1969, this astounding circuitry makes a relay operate on 3 Hz cycles. The relay is of the high voltage type of the time.
For those who still listen to vinyl records, but because they are old and worn, they have a lot of...
The oscillator shown in the figure generates a 1 kHz tone that is reproduced on the speaker with...
This circuit can be used as a residential doorbell. We found it in an English publication from...