This is not a song from Kraftwerk but a real little Geiger counter...
While wandering around once again, I came across this kit, with the specificity "Arduino Compatible", which I bought.
I figured it must have a UART and it would be fun to interface it with a PC or something.
No UART in sight, not even a microcontroller, just an open collector output which is briefly grounded at each sound signal.
The kit arrived assembled (:-() and is very clean.
The assembly is based on a cheap Chinese tube.
The high voltage, supplied by an oscillator and a charge pump, is adjusted via a potentiometer, with measurement on an incorporated divider bridge. Convenient.
The only thing, the tube supports were not at the correct center distance, a modification was necessary.