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 20 MHz Colpitts Oscillator (CB6506E)
Found on Popular Electronics from the 1990s, this oscillator uses a general purpose transistor. The...
1A voltage follower (CB21073E)
This circuit was obtained from National Semiconductor documentation from the 1990s. The circuit has a...
H Bridge Current Monitor (CB5393E)
We found this circuit in a 2005 Linear Technology manual. Observe the component values and...