This 1965 Philips circuit uses old company transistors like the BFY51 and BFY50. The circuit is powered by 12 V and the power gain is 8.9 dB.
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...
This circuit is from an English publication from 1973, but can be easily assembled today. 2N718 can...
The figure shows how to connect a relay to obtain the latch effect. The circuit is from an...