Two-input amplifier (CB21661E)

The critical component of this 1967 amplifier is the driver transformer. The circuit has both high and low impedance input.

Spy Tunnel Diode Transmitter IV (CB19428E)
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...
4-band photometer (CB8341E)
Obtained in a 1968 Electronics World, this circuit uses transistors from the time and the sensor...
Peak indicator with hysteresis (CB21973E)
The basis of this circuit is a CA3130 operational amplifier. The transistor can be BC548, and the...