When an amp puts out 90 watts....

Ralph, re your post about 4-16 ohms at various frequencies not being a problem if the tube amp has 10db or high NF seems correct. As you know, I posted links to Soundstage and Stereophile bench tests of the ARC VS-115 and Ref 150 tube amps. Both amps use similar amounts of NF (about 12 to 14db) and have similar output impedances of about 1 ohm off the 8 ohm tap. The output FR of both amps was about +/- 1 db over the audible FR spectrum when driving a simulated speaker load that had similar impedance fluctuations as staed above. Atkinson said the output FR might even be tighter off the 4 ohm tap where output impedance was 50 to 60 percent of the 8 ohm tap output impedance.

Got it Ralph. But outside of the few exceptions like your OTL type amps, a pure "Power Paradigm" amp that doesn't use NF and that has a somewhat high output impedance will likely choke on speakers that were designed to be driven by low output impedance high current SS amps. Especially if the speakers have wacky impedance and phase angle curves.

You and Al used a jackhammer to get through my thick skull to get me understand the basics of these various interactions. And . . . thanks to the Soundstage and Stereophile bench test reports on the ARC VS-115 and Ref 150, I finally got to see numbers wrapped around the theory.

Folks who are interested in tube amps should keep this stuff mind. Not sure how Zobel networks works, but for folks who are interested in tube amps like yours, or other zero feedback tube amps, it might be worthwhile for those folks to get up to speed on that EE variation.

Regards,

Bruce