This circuit is from a 1977 Signetics integrated circuit manual. The output transistors can be BD136 and BD237 and the symmetrical supply can be from 6 to 12 V. The voltage gain is 10.
Using an operational and a transistor according to the maximum desired current, this circuit...
In this circuit R1 has 2M5, R2 and R3 are 5M obtaining a detection current for the diode of 0.5...
Found in 1966 General Electric documentation, this circuit uses solicon unilateral switches (SUS)...