This circuit is from 1973 documentation. The transformer has 500 mA of current and the transistor can be the TIP32 mounted on a heat radiator.
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...