This circuit was found in a 1969 Mullard documentation. Used transistors can be replaced with modern equivalents. Output transistors may be BD135 and 136 with heatsinks.
This is a simple voltage tester for voltages from about 2V to about 15V with the indicated...
The gain of the Operational Amplifier in the figure is given by the ratio between R1 and R2. In...
This electrochemical circuit monitors the conductivity of the oil indicating when to change it. The...