Phone circuit (CB8709E)

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

Bass and Treble Control (CB11159E)
This Baxandall tone control was obtained in an Argentine publication from the 70s. The circuit uses...
Bistable Neon (CB10505E)
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
35W Transistorized Amplifier (CB1322E)
This powerful amplifier with output in complementary symmetry is from an old documentation....