Which device is high-voltage but low-current and commonly provides assist at relatively low cost?

• A. Spark-gap oscillator
• B. Transformer
• C. Induction coil
• D. Rectifier

Answer: (A)

When starting a TIG arc, you want a brief, high-voltage pulse to ionize the gas path, but you don’t need much current. A spark-gap oscillator does exactly this: it charges a capacitor from a low-voltage source and, when the voltage across the spark gap reaches breakdown, a rapid discharge creates a short, high-voltage pulse with very limited current. That combination—high voltage for initiation, low current, and simple, inexpensive construction—makes it a common, low-cost assist device.

A transformer is designed to deliver controlled welding current, so it isn’t just a quick high-voltage pulse. An induction coil can generate high voltage but is bulkier and not as straightforward for a cheap arc-start; a rectifier converts AC to DC but doesn’t provide the necessary high-voltage pulse for initiating the arc.