In use telephone indicator (CB8657E)

Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be used with extensions.

Incandescent Lamp Flasher (CB528E)
This low voltage lamp flasher can be powered from 12 V supplies. Frequency is adjusted by P1 and...
Alarm Siren (CB19985E)
The transistors in this circuit, found in an American publication in 1975, can be replaced by...
Audio Oscillator 2 (CB12907E)
This circuit, from an old publication, can also use modern transistors. Note that the unit is...