Extremely easy extremely powerful flyback driver

2N3055?

You tested that voltage with a meter IRL?

What?

VCE peak = 1 MV

And does not oscillate for long

Now base voltage is 10v max and the oscillations lasts for a long time. Thank you for making me notice that! ;-)

won't work well with 2n3055, it won't switch that fast and it's hfe will drop to around 20 or so. above 16kHz the voltage doesn't build on the secondary winding due to the capacitance on it, so it won't get more than a few thousand volts and the power is absorbed by the core instead. if you do manage a spark across the secondary, the massive DC current unloads this energy out of the core, pulling a huge current up the primary side through the BC and EC junctions in reverse. 2N3055s don't last long in circuits like this sorry. they're nice old transistors, great for audio circuits and current mirrors, they don't tolerate abuse and they're expensive for what they do. use a power mosfet instead if you want to make high voltage sparks

And if i use some of those big transistors from crts?

Or from an atx like 13009 or 13007?

Niki, it was your recommendation!!!! Do not be like Buggzy, and recommend things you never tested!

Build it ; test it ; simulated it and make your recommendations to the community!

Ok ok i got the lesson :-)