Bedini SSG Tuning Index - Transistor Selection and Base Resistor Calculator

Let's compile a definitive index of transistors that work in the Bedini SSG circuit. The classic MJL21194 is highly reliable, but many are using 2N3055 with mixed results. What base resistance values are you finding work best for each?

The 2N3055 is okay but it lacks the high voltage breakdown rating needed to withstand the inductive spikes if a battery accidentally disconnects. The MJL21194 can take 250V continuously and has a better gain curve under pulsed loads. For MJL21194, I find a base resistance between 470 ohms and 680 ohms works best. For 2N3055, you often need to drop to 100 ohms to get solid switching, but it runs much hotter.

I ran side-by-side thermal tests. The 2N3055 draws about 15% more current from the primary for the same charging rate, and runs at 52C compared to the MJL21194's 34C. Stick to the MJL series if you want efficiency. Adding a 12V bulb in series with the trigger winding also helps self-regulate the trigger as the RPM changes.