Lidmotor's Penny circuit help needed.

[Dark Alchemist]

1us

[Dark Alchemist]

10us

[Dark Alchemist]

50us

[Dark Alchemist]

100us

[TinselKoala]

Weird. Thanks for doing that, even though it leaves me a bit more confused about what is going on.
The _average_ value of that oscillation is at your 0.5 volt supply voltage, and the peaks never seem to go high enough to overcome the LED's forward voltage. So this signal could not be lighting up the LEDs, especially not 4 in series.

Could you please try this now: Set your trigger voltage to some value decently _above_ the peaks shown in the traces above. Try setting the trigger to +2.0 V, and the timebase back to 1 millisecond per division, and wait a bit to see if anything shows up.  What I am thinking is that perhaps your circuit is oscillating in bursts and we are missing the voltage peak that lights the LEDs.

I've rewired my JT testbed to correspond to the circuit in your schematic, except that my inductance is still a bit low and I don't have the right transistor. But with 2n2222 I get this: the circuit flashes both the single LED or the 24-LED 2series-12parallel array at about 1 per second. The flashes are fairly dim. If I use the MPSA18 the flash rate increases to perhaps 2 per second. I've got a bunch of low-voltage "dead" batteries and I found one that indicates 0.7 V open-circuit, and this battery powers the circuit fine, but another one with under 0.4 volts won't. I don't have an easy way to provide a precise 0.5 volts supply at the moment, but later on tonight I'll try to make one.

Now, I've just used the "single shot" capability of my Link DSO to capture the waveform of a single flash. It's pretty interesting.