Now, a few comments on loading, since you mention that power might go up since the load went up to 11K. With all else being equal, as the load goes up, power goes down.
From my simple point of view, I imagine the ratio of tube output Z to tranny load Z and try to imagine what happens to a tube that is loaded with too low of speaker Z, which when reflected into the tranny lowers the load Z and pulls more "power" from the tube until it melts or blows the VC of the speaker. So I further extrapolate from that to say if a 10K tube is loaded with a 5K tranny, or a 2.5K tranny, the power through the tube rises... above design. I may be completely upside-down in my logic about that. Perhaps I should see it as if the tranny primary were a straight wire, there would be no power transfer at all, but what about current? Not sure what the result of a primary shorted to itself would be on tube current, other than the obvious reduction of DCR.
I was doing my comparison of the 7189 characteristics with EL-84 characteristics with data sheets that specified K biasing and with the EL-84 the Za-a was 8K regardless of the tap point but the 7189 rose to 11K Za-a when in 43% UL mode. That sheet didn't show a Za-a when connected to a 23% tap, unfortunately... or this question wouldn't have come up.
I really appreciate the time you take to post such thorough replies. I think it will all gel someday.
Headed for Shelby HF tomorrow.
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