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.
The signal from this circuit found in a 1968 Electronics World is sinusoidal and depends on the...
This circuit uses a sensitive vibrator that can be made with a reed-switch to activate a relay from...
This amplifier can be powered with voltages between 2 and 5 V with power up to 100 mW. The minimum...