This circuit is from an Electronics World of 1968. The transistors are of the time and the power is supplied with a voltage of 40 V. The circuit is high fidelity.
This circuit can test quartz crystals from 3.5 to 90 MHz. Its supply can be made with voltages from 8...
With a touch of the sensor, the output of the 4013 changes state from high to low or vice versa. In...
Using comparators, this circuit can be used in a measurement bridge. The balance indication is...