Motorcycle headlight monitor (CB9117E)

This simple circuit was found in Popular Electronics from the 1980s. The circuit uses an LED as an indicator.

Source Follower FET stage (CB4687E)
In the figure we have an amplification stage with FET in the source follower configuration. The circuit is...
Relay Drive (CB13907E)
This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by...
Nonlinear Gain Amplifier (CB6130E)
This nonlinear gain circuit was found in a 1965 Electronic Design. The configuration can be used...