Here is a very old unregulated (1960's) dc to dc converter (switching mode power supply) circuit using two 2N3055 transistors to generate about 300 volts from a 6 volt battery
. This circuit uses a standard 60-Hz transformer, and the switching frequency (determined by the resistor and transformer inductance) is several hundred Hz.
This evolved into the Delta Mark Ten kit about 1968. The Delta kit had a pot core transformer instead of a standard 60-Hz transformer.