Phone circuit (CB8709E)

With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a basic intercom.

12 V Flasher 4001 (CB15441E)
In the figure we show another interesting application for integrated circuit 4001. This circuit...
15W Hybrid Amplifier (CB17493E)
This amplifier, common in 1986, uses a hybrid integrated circuit that can offer some difficulty to obtain...
RF detector (CB11517E)
In fact, it is a RF field indicator with an operational amplifier equivalent to the 741. This...