Watched this one today: EEVblog 1409 – The DANGERS of Inductor Back EMF.

I learned about back EMF, freewheeling, snubber, flyback, or clamping diodes…

In this video I also learned that BPJ transistors have a storage time, or switch off time, in the order of microseconds, e.g. 5 μs. That probably explains what I saw when I tried to measure the frequency response of my DTL OR GATE.