quote debe:
Did some tests on the 3 original Atom modules I dismantled switching transistors. Using a Digitec Component tester. All test as NPN darlington, & Hfe is not accurate due to B-E resistor of 2.2K, all have internal protection diode C-E. Two of the modules had a custom transistor marked A1, Hfe 8 Ic test 2.5Ma B-E 1V. Other one marked A2, Hfe 9 Ic test 2.5Ma B-E 1V.
I’d always assumed higher gain was needed. Here are some current "ignition darlingtons":
