Found in a 1980s American documentation, this circuit operates with 5 V signals requiring 55 cycles of 500 Hz for tone recognition. The circuit can be adapted to operate with other frequencies.
This circuit turns on a lamp after the time set on the potentiometer. The circuit is from a Radio...
This signal amplifier for ATV in the 427 to 439 MHz band was found in a magazine 73 for radio...
This amplifier has a few Watt output, using old transistors. The speaker is 45 ohms, but with...