Metal detector receiver (CB22457E)

Found at Popular Electronics this receiver is used with a transmitter for quadrature-coil signals.

Tunnel Diode Audio Amplifier (CB13337E)
We found this interesting configuration in a 1976 technical documentation. Equivalent diodes can...
Full wave rectifier with an operational amplifier (CB8070E)
Indicated by the Maxim Engineering Journal in the 90's edition, this circuit uses only one...
Photodiode Amplifier (CB15651E)
The gain of this circuit is given by the value of R1 that depends on the current in the...