TOM, I've encountered simuliar problems with those old TIG machines, the main problem is the old Dial Arc machines do not have square wave arc design and in those older machines do not have a real good HF arc compared to the modern machines. There are some things you can try, first and foremost is cleanliness in TIG welding aluminum is the single most important step, a clean stainless steel brush is mandatory!!!!!!! Don't forget to clean your filler metal ( with 00 grade stainless steel wool )and a clean shield cup as well. I also had a better chance at a stable arc and better tungsten ampacity with 1 or 2% TH and balling the tip, 3/32 dia.. At those amperages you should not have any arc starting problems, Check the gap in your HF unit, take them out , clean ( with 220 or 260 grit emery cloth )and reinstall, I believe the gap is .050 inches, you might want to consider using a run tab at the weld start, at half your weld amperage, start the arc and use the HF to give your weld one last cleaning before starting the weld. If you have the opportunity, try Argon 75 - Helium 25%. You can get more heat to the weld and travel faster because of the properties of the Helium in a welding arc. Helium is an excellant conductor of heat. The main consideration is I don't know all your welding variables and do not have and accurate evaluation of everything. Hope this helps in some small way, work at it ............
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