That can be a problem. A balled tungsten on AC has a very specific amp range where it will work. A heavier diameter pure or zirc tungsten will not run at low amps. If using a foot amp control, you are starting at low amps and ramping up. The time you are at lo amps causes the instability.
On heavier material, a quick fix is to "nail' the foot control and then back off to a good running amperage.
Working on radiators, intercoolers and other thin stuff, we do not have that luxury.
Two remedies I can recommend.
1. Use a zirc, lanthanated or ceriated (stay away from pure-it just doesn't run as well as the others) in the proper diameter for the amp range you anticipate. I've run zirc as skinny as .040 with good results-off a Miller Syncro 250, no less.
Amperage ratings for tungsten are easily available from most of the major welder mfg, or got to profusion.com
2. If a larger tungsten is all you have, grind it to a point much like you do when welding DC, leaving a very slight flat on the point. Find a clean piece of material and just use enough amps to "ball" this point just slightly.
Start your welding, the ball will start well, but only get as large as needed. If you are easy on the foot control-don't go higher than needed-you will have a "custom pointed electrode" that should work well.
I weld a number of intercoolers used on the turbo japanese car setups. For the most part, 3/32 pointed zirc works well. A few designs require 1/16.
Keep in mind that in this type of work, especially on AC, a very short arc is essential. If your arc is over 1/8" long-it is too long. Keep it tight.
Hope this helps a little. Keep in touch-let us know how you make out!!
Good Luck
brande
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