Phone circuit (CB8709E)

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

1 to 100 mA Shunt Regulator (CB15573E)
The shunt type regulators are connected in parallel with the load, deflecting the current to...
Precision Power Supply (CB21573E)
Using the LM317 (or LM350), this circuit is based on precision regulatory components such as those...
Solar Frequency Standard (CB21951E)
This solar cell powered circuit generates a standard 100 kHz signal. The circuit is from a 1960...