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.
This circuit was obtained in a 1985s English magazine. The circuit can still be assembled with...
This circuit was found in a 90s American documentation. The circuit uses an LED that can be of a...
The circuit presented is from the National Semiconductor's Linear Applications Handbook of 1994. We...