This amplifier for instrumentation with very high input impedance was found in a manual of JFET circuits. The operational ones used are current and the power supply must be symmetrical.
This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio...
This circuit indicates when the monitored voltage drops below the value determined by the divider...
This circuit, from a 1975 Motorola manual, uses a power Darlington transistor of the time. We can...