This circuit was obtained from American documentation from the 1990s. The transformer can be a car ignition coil that works like an autotransformer. Q2 must be equipped with a heat sink.
This circuit with unijunction transistors was found in a documentation from the 80's. The trigger...
In this circuit of an old American documentation, the input impedance is the same as the output...
In the figure we have the way to obtain a voltage of 18 V from a 6.3 V transformer with central...