Why to use 7 separate transistors in SG?

[Oscar]

I am a beginner and read about these both SG books. My mind is open for new things like these Bedini inventions. One thing is circulating in my mind concerning the use of 7 transistors in SG instead of one big IGBT or mosfet. Since John has selected 4 MHz fast transistor, is it faster to switch off than one individual e.g. IGBT? I assume IGBT has always bigger internal gate - source capacitance causing slower switching times. Is this a reason to use separate 7 transistors? I understand that one of the most important thing is to perform a fast switchings to release radiant energy before the electrons start flowing in circuit. I looked at the datasheet of one IGBT and switch off times are somewhere couple of hundreds nanoseconds.

[John_Koorn]

IGBTs or FETs are not good with switching large inductors, the radiant spike gets into the junction and can kill the gate. You also can't get around the gate capacitance problem. Save your IGBT or FET for dumping capacitors.

if you scope an MJL21194 that is switching a coil using the SG circuit, you'll see that it switches pretty fast.

John K.

[Oscar]

Thanks John about quick reply --> I am surprised! OK, this explains the reason to use MJL21194 transistor.
And it is almost twenty years I visited in Lilydale near Melbourne. Good memories...

Kind Regards
Oscar