This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
Epson SG 8018 Epson Crystal Programmable Oscillators Available from Mouser Electronics, these...
When the lights turns off this circuit will produce a sound like a cricket. When the lights are...
This circuit appears elsewhere on the site. The circuit shown is from an American 1980s...