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 was found in a 2000 Poptronics. The magazine no longer exists, but the circuit can be...
This 80's circuit has an input resistance of the order of 880 M and gain 10, using operational...
This circuit can be used in a toy organ. The frequencies are determined by the capacitors selected by...