This circuit can be used as a lockable shield. A pulse activates the relay that remains on even after the pulse disappears. The transistor is general purpose.
This circuit is from a Popular Electronics from the 90s. Its gain is 22 dB and can be used as a...
This simple source is suitable for audio amplifiers providing an output voltage of 32 V with a...
This circuit is from the 80's but uses common components today. The relay is voltage sensitive...