Hi. I just opened up a HF TIG arc starter made by 21st Century (brand Power Kraft). It works fine, but makes too much EMI noise. Some of the causes were evident: no HF chokes on the mains transformer secondary and no line EMI filter.
What I was curious about was the absence of a HV capacitor. Most TIG arc starters have a large HV capacitor, usually mica or doorknob type. This one only has two 0.1 uF 600 V film capacitors. One is a bypassing cap between the power leads, so it sees a smaller voltage drop. The other is connected across two leads of the air core coupling transformer. The other two leads go to the spark gap, which is customary. The secondary of the transformer is placed in series with the welder power supply, which is also customary.
Is anybody familiar with this design? Is the resonant circuit the alternate winding operating at a lower voltage, or is the air gap transformer self resonant?
Such a design would save the expense of a HV capacitor, with the additional (possibly slight) expense of a specially wound coupling transformer.