Joule Thief: Supplement: NE-2 Voltage Threshhold Determination
Here I take one of the NE-2 bulbs and show how to find out what the voltage required to turn it on is. I used 2 x 220K resistors to limit the current and hooked the bulb and resistor across the output from the old GenRad variac, with the El Cheepo DMM monitoring the AC voltage. The bulb lights at right around 91 volts with this setup. I bought a double handful of these bulbs years ago at the old Mike Quinn electronics surplus house in the Bay Area. What a place, too bad it’s gone now. I think I paid a nickle a piece for them, or maybe just a couple dollars for the whole lot. I still have around 70 left, that aren’t in use for one thing or another. They are very handy.