Found in a 1965 CQ magazine, this circuit uses period components. The unijunction transistor can be a 2N2646 and the relay has voltage according to the supply.
This circuit multiplies the input resistance of an operational amplifier. As the indicated...
This conventional flip-flop configuration with two transistors was found in documentation from the...
The input impedance of this amplifier is of the order of 1014 being the same indicated for pH...