Suggested by Philips documentation from 1968, this circuit uses components from the era that can be replaced by modern equivalent types. The double transistor can be replaced by a matched pair.
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...