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.
We found this circuit with a Q factor of 25 in the Linear Applications Handbook by National...
This circuit was found in a Japanese publication from 1971. The circuit uses components from the...
When this circuit is activated the LED flashes for a moment indicating that the function has been...