I gleaned a bit of incidental information while studying up on the ol' PRRI and it's ancestry. I can't recall where, but during a read on the cathodyne-style phase inverter, I read that at best that elusive swirly tone can be had, while at worst that nasty doubling effect will occur without sufficiently augmented grid resistance - and somewhere in the middle, most of us live with neither artifact. Well, call me crazy, but I'm in for the swirl. The only time I've experienced that heavenly condition was with my first build, a 5E3 clone (at or near "12") that I assembled using Hoffman's catalog and a Weber Blue Dog. I remember first switching it on using a broomstick as I sought defilade behind a chair lol. In fact, it was that sound that would eventually precede my rectifier or Brimar 6v6's melting down and taking the PT with it. There's gotta be a way to ride that edge without going nuclear. Have any of you successfully gotten a cathodyne PI to intentionally and safely behave this way? Is this swirly goodness simply the "double frequency" blocking distortion occurring while both frequencies are ever-so-slightly misaligned or out of phase? Or is it just the nature of the TwdDlx and it's marginal filtering? I've never had that sound at my fingertips since that amp melted down and it's making me wonder what's possible with this PI configuration. I dont plan on modding this PRRI; I've got a Univibe clone for the swirly stuff. Maybe another 5E3 is in order.