NO BATTERY JOULE THIEF FLASHLIGHT (2.7V 400F SUPER CAPACITOR)
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Killer Deal on 400F caps $4.82
When you order - attach a note to shop owner stating you want the 400F not the 360F
Cheap LED bulb $5.69
The inductor is a power ferrite (black core I think) wound with (many) 18 gauge turns, bifilar. the transistor is MPSA06, but could be any NPN, likely... I should actually see if it runs hot, initially. Probably does. A TIP transistor probably would not heat up. 10k pot. Extra tiny cap on the power rail for smoothing / impedence matching.
Runs bright for 30 mins and continues on producing useful light for nearly 2 hours. 6 hours later it was still glowing away with the cap reading .420V.