This audio configuration of televisions from the 1960s was found in a Mullard transistor reference manual. Transformers are the critical components.
In the figure we have a classic Clapp oscillator configuration for a frequency of a few tens of...
This circuit takes advantage of the inductance of the phone in the resonant circuit. The circuit is...
In the figure we have the way to increase the voltage of a 78xx by adding a zener diode. The...