This high impedance amplifier is from 1985 documentation by General Electronic. The amplifier with FET at the entrance is from the period and the source is 9 V.
The circuit in the figure is based on an LM101A; diodes can be replaced with equivalents. The...
This circuit, with magnetic sensor, uses an operational amplifier of the time. The circuit is from...
Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is...