Diathermy machines have 2 poles, and they usually use a pancake coil for output at 150,000 V. But they also come with intermediate settings to have D'Oudin voltage and a lower voltage too, but at high current. You easily cook meat with the low voltage terminals.

Rife simply used the first transformer only of the 3. He custom wound it in order to have an output of 5,000 V.
That is just a little above the requirement to get helium full spectrum down to soft x-rays.
If you were to use argon, you need a much higher voltage (15,000 V should suffice).

The good advantage in using air, such as in violet wands, is that you can have a very broad spectrum. CO2 naturally has a broadband spectrum that resonates with microorganisms.