I learned something interesting today, that is probably common knowledge to most welders. I have a friend that welds, mostly on marine equipment. He came to me wanting a switch installed on his tig torch to help him tig some anodized aluminum. He has an HF251-D1 high frequncy unit and a Trailblazer302. I found a schematic for the High frequency unit, but was a bit perplexed as I couldn't locate any semi conductors that I thought would be used to generate a high frequency. Well, later in this process I found out that the thing operates like a tesla coil with a spark gap to create the high frequency.
Now, in order to figure this thing out I wanted to see it operate, So the welder went on to show me and it would not work. He could not get any high frequency arc. He said it worked fine last night, Ok, "so what did you change"? He had added about 70 feet of cable, OK, so let's take that cable out. So now the HF works fine, It turns out the cable was wound up making an inductor that would not allow the HF to operate properly. Once the cable was straighted out it worked fine. So.. the HF unit uses a spark gap to create HF and you can't coil the wire and use an HF unit. I thought it was interesting. Mikek