This circuit is from a Radio Electronics from February 1959. The circuit has a speaker output and good sensitivity. Power is supplied from a 9 V battery.
We find this circuit in an old documentation, but it can be implemented with modern equivalent...
This circuit eliminates transients that are 10% above the zener voltage. The transistor must be in...
A solution for using more than 6 channels in a tone-modulated system that uses LM567 as decoders, is to...