I finally got around to connecting these amps directly to the Ushers using the Speltz zeroformers, and Ed's crisscross speaker connection. I went right for the max 4:1 ratio, not yet pulled back to the lesser ratios yet. The autoformer definitely gives more control and detail in the bass. Maybe slightly thinner in the mids, hard to tell. The autoformer multiplies the impedance of the speaker by a constant factor depending on which taps you connect to the amp. So with 4:1 tap, impedance at every frequency is multiplied by 4. The minimum impedance of the speakers becomes 16 ohms!
With an easier load the amps can play louder without distortion. I can use the high impedance tap on the amps output transformer, and fiddling around with feedback level further fine tunes the amps to the music at hand. I think in the end they are not quite enough power for me though it is borderline, and most of the time it is enough. Symphonies need a little more. But the autoformer makes a huge difference. Actual output impedance of these amps is 1.8ohms in PP mode.
The zeroformers don't negatively affect the sound of the amp as badly as anticable speaker wires did. I don't hear the ringing, but it's still not the JPS sound.
300B is a truly beautiful sound. Clear and powerful, but intimate and "special." The smooth relaxed sound is unlike anything I have heard before. Class A is the way for me. Same feeling I heard on Pass F5 at RMAF08 but more gain and more soul with the tubes. It is definitely warm and a bit glowy, which works well sometimes, and not others. Even though I usually don't like modern female singers after working with the primadonnas offstage for many years, I have to admit the sound of estrogen is seriously sinful on this combo, Usher and Manley 300B. No preamp.
If I crank up the feedback and use the amps 4-8ohm output tap I can play rock very convincingly, at pretty loud levels. Not as clean bass as some SS amps, but very authoritative bass, and plenty enough texture to satisfy.
I'll book a g2g after TG.
