This interesting circuit uses a sodion valve that we have already described in an article on the website. The circuit uses several batteries for power. The phone is of high impedance.
Originally this circuit was indicated to be used in a garage door control, but it can be modified for...
This conventional oscillator with the 741 can be precisely adjusted to produce a 400 Hz signal. The...
This current-limited circuit was found in a Popular Electronics from the 90's. ...