2N5657 is cheap and available - very-high voltage transistors in TO126 or TO225 are not "common"(*) - I found KSC5026 as a possible replacement, but it has higher gain and is more expensive.
(*) The package pin spacing is rather dubious for 350V.
(*) The package pin spacing is rather dubious for 350V.
Many thanks. I should have said there is no real packaging limitation, as I just have the PCB and the pads are right along the edge for heatsinking.
Any reason I couldn't use a TIP47 through 50? It's TO220 and the pinout's reversed, but again that can be overcome by the physical mounting.
Any reason I couldn't use a TIP47 through 50? It's TO220 and the pinout's reversed, but again that can be overcome by the physical mounting.
If you want cheap TO126, use KSC2752. Made for low power electronic lighting ballasts, therefore cheap and plentiful, but also works well as an amplifier.
TIP50 is my go-to at higher currents and if I actually need to pull heat out of it.
TIP50 is my go-to at higher currents and if I actually need to pull heat out of it.
From the schematic, the transistor needs to have 360V Vceo as a bare minimum (in practice, 400V would be half-reasonable).
The pic is tiny, but I think I can see a 370V spec in chinese: this would mean specially selected 2N5657.
The TIP47 doesn't qualify; the TIP50 would be just OK at 400V.
Small mosfets could also be used, but with a gate protection