solder hack pin
I love steampunk and also tubes, brass etc. and some years ago I played a lot with joule thief circuits. Not only to drive a LED with just 1.5V but also to ignite little plasma inside of neon bulb lamps. There are many sites describing these high voltage joule thief circuits. I found this one from high power joule thief https://overunity.com/6123/joule-thief/15015/ and played a bit with this circuit on my breadboard. You can find also a nice article from Alan’s Lab but I was too lazy to wind a triple coil: http://www.vk2zay.net/article/30.
You can see the result in the circuit picture.:
Circuit of the “I can
solder hack” pin. The windings are twisted in their polarity. So you have to try in which polarity it works. The neon bulb lamp has no polarity. Due to the fact that you use a DC voltage only the gas around the “negative” pin inside the neon bulb will glow.
The main differences compared to the circuit from high power joule thief are:
The transistor is a BC574 instead of a MJE13007
My toroid has more windings. First I wound the secondary coil with 0.3 mm isolated copper wire around a 13 mm outer 6 mm inner ferrite toroid with 6 mm height, then over the secondary coil the primary with 0.5 mm isolated copper wire.
The capacitor is bigger with 0.068 µF/250V.
The dark side of the pin. Battery was removed. The toroid is the biggest part, to spare some space on the backside the BC547 was inserted into the toroid. To have a GND rail, a part of the outer tin track was cut and directly used as connection for the capacitor (orange) the emitter of the transistor and as ground for the neon bulb. The original battery holder was replaced by a short u shaped wire with 0.8 mm in diameter. Positive pole of the battery is up (the wire).
Funny was the behaviour of the circuit. After building I inserted a fresh LR44 cell (but I missed to measure the voltage), the neon bulb was glowing. After some minutes the neon lamp starts to blink due to the voltage drop by a high current. With a lab power supply the circuit needs 320mA with 1.5V. The blink frequency is also changing over the time from fast to slow or vice versa. Sometimes
If you have a look on the output, measured with connected neon bulb lamp you can see this in the oscilloscope:
Output of the circuit measured direct on the neon bulb lamp. The voltage of the battery was 1.158V
In the end it was a nice Sunday afternoon project with a lot of fun and also a bit of debugging.