This circuit takes 3.7vdc and converts it to about 18kv. The transistor is used for the plasma speaker. It’s basically a Single-Ended Class A Audio Amplifier. The 500-ohm pot adjusts the voltage sent to the converter. The pot must NOT go over 500 ohms because then the voltage could be too high. The circuit is currently untested but to believe it may work. Also LM338 is used instead of LM317 because of the high current draw.
Keep a lookout for when I get it built and upload photos and a video. I thank flyback for reminding me about the inductive kickback voltage so I put a diode in reverse bias across the power inputs on the converter. The converter cat# is HVS-01 on allelectronics.com
YouTube video part one Total cost:$50.21