Integrator with bias compensation (CB20991E)

This circuit was found in a Popular Electronics from the 90's. It can be implemented with equivalent operational amplifiers.

Power Failure Alarm (CB25348E)
This circuit triggers an alarm when the mains power is cut off. The circuit was found in the July...
Tuned null indicator (CB22314E)
This acutely tuned circuit was found in American documentation from the 1960s. The transistors are germanium...
MW Transmitter (CB20809E)
This small AM transmitter was found in American documentation from the 1980s. Transistor support...