Fluorescent Tube Oscillator

This project is yet another spin-off from my Cosmic Ray Detector Project. I recently stumbled across this as an unwanted artefact in the detector and so I thought I'd let people know as it might make an interesting project for electronic music people.

(Yes I know the same thing can be made very cheaply with other components, it is just a kooky oddity)

When exploring into this artefact in detail, I found I could make a very effective relaxation oscillator using only a fluorescent tube and a couple of components, which will resonate at a specific frequency and with few additional components the frequency and distortion could also be adjusted.

I imagine it would make a very strange looking electric instrument indeed arranged with a number of tubes in front of a keyboard and a panel of control knobs. Where the tubes would glow and flicker as they where activated.

Here is a bench top test, the filament voltage is set between 7 to 9V in this example it is set at 8V just a very faint glow, the capacitive trigger is set at -350VDC (copper tap around the tube). the Cathode to Anode Voltage is being adjusted from 2V to 100V and oscillation begins at 47VDC up to 100 and down to about 33V where it ceases in the video (Note the distortion begins around 45V and down).

The circuit is basically a Thyratron Valve driven relaxation oscillator and emits a Sawtooth waveform. R1 is 10K ohms and C2 is 10nF (note voltages are estimates and will vary from one fluorescent tube manufacturer to another). The foil tube coupling could be replaced with wire mesh to allow the light to be seen easily.