Phone circuit (CB8709E)

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

Nanoammeter (CB12009E)
This circuit allows the measurement of very weak currents indicated on an analog instrument or...
Preamplifier with tone control (CB9517E)
Found in National Semionductor documentation this circuit combines a tone control with an...
RF Generator (CB7424E)
Found in a 73 magazine from the 1980s, this circuit generates signals from 3.2 to 22 MHz. FETs can be...