Beware of main curent loop diode capabilities.horizontal output line Booster-Damper diode is a device created to operate under such conditions and is a nuber one candidate for this job (typical reverse blocking spike will hit around 1kV when good quality parts are used.)
Transistor current transfer quality factor (alpha parameter) is not so important here having very little effect on performance. Even very low alpha HV power bjt's (like mje13xxx popular power transistor family)will perform nicely.
High power efficiency came from tuned load that make perfect use of transistor extremely high resistance gain that give a max possible power transfer from source to load using as a driving signal sum of return currents that give required base loss resupply plus safe excess charges for maintain hard driving positive feedback capable to deliver 99% of saturated power.
The transistor power loss is only represented by integrals of CE voltage drop times main current plus base curent times BE junction voltage drop. As transistor is in most simple basic configuration there are no loses for extra bias circuits and turn on/turn off loses are almost not important cuz when care is taken to maintan low impedance for base ground point transistor gains impresive turn on/off times due to unblocked path for stored charges capable to discharge from base area straight to ground freely not disturbed by any nast ohms that create "road blocks" on route slowing things down
This device will work way much better when a momentary starter Button became pressed for a second or two ;) thank you for u attention ;)
