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.
This circuit generates short pulses. The transistor can be a 2N2222 or BC548 and the frequency is given by...
This traditional phase displacement oscillator circuit was found in a documentation from the...
This circuit causes a set of LEDs to flash sequentially in a move that is modulated by the audio...