Metal detector receiver (CB22457E)

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

1-Transistor Amplifier Stage II (CB19570E)
Unlike the previous one, this circuit uses only one resistor in the base polarization. The...
Mechanical reverb (CB22208E)
We found this circuit in an English documentation from the 80's. Transistors can be modern...
Temperature Relay (CB24076E)
Found in the August 1970 Radio Electronics magazine, this circuit uses a CA3018 with the trigger...