This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
This variable oscillator with power step for alarms was found in an American documentation from...
This circuit was found in a 90s Radio Electronics. It produces an ultrasonic signal in a special...
This circuit is only used for resistive loads such as incandescent lamps. The bridge diodes can be...