This circuit is from a 1969 Electronics World. The transistors may be modern general-purpose equivalents. The circuit is for frequency ranges between 250 Hz and 250 kHz.
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...