In a message dated 4/3/2005 10:14:04 PM Central Daylight Time, N4BUQ at aol.com writes: Isn't a dirty ground strap also one cause of PTO warble? Barry(III) - N4BUQ Yes. But in the Progressitron's case, I believe it was a quality control problem. I've owned R-390A's with 8 Progressitron PTO's, 7 of them had the bad solder joint on the caps. And, they all warbeled. Les