This circuit was found in RCA documentation from the 90s. It consists of a power control for a load based on a thermocouple. The integrated circuits are uncommon today.
This circuit detects light variations using two LDRs as sensors. Operational amplifiers and...
The circuit shown consists of a power stage for relay excitation. 2N3053 can be a BD135 and 2N406...
This circuit was found in Mullard's 1960s transistor manual. The circuit uses germanium...