SET vs OTL

I have the Tannoy Turnberry SE

That speaker seems a bit on the low side of efficiency (93dB) for an amp of only 7-10 watts! Nice speaker though. I'd be putting at least 10x more power on that unless the speaker was in a small room.

This is what I know about the Tenor (we had a few in here for service some years back): It is a differential design but using a circuit similar to what is in the BAT VK-60, which is to say two cascaded gain stages driving the output section. That is how our very early amps worked but back in the early 1980s I realized that there were too many problems with the approach (in particular DC Offsets which would result in unequal drive to whatever stage was succeeding, resulting in distortion, especially the 2nd harmonic).

The 2nd harmonic suggests a quadratic non-linearity is present. The differential design suggests a cubic will be present also. Further that amp employs feedback (although not nearly as much as is needed) while the WAVAC does not. I would expect the Tenor to be fast and transparent but a bit dry, perhaps a bit bright and less engaging compared to the SET. Do I have this right?

You are correct @atmasphere that Tenor had the better PRAT. But it did not control my speakers as well as the 10 watt Wavac. That was wierd. It also did not sound as illuminated from within as the Wavac. I have again noted this difference between typical SET vs Push-Pull amps. SETs illuminate the entire spectrum evenly (DHTs more, non DHT) but push-pull amps have a darkness to the presentation. Can't explain it well. That is also one reason SETs sound more vibrant & energetic compared to Push-Pulls.  

That is also one reason SETs sound more vibrant & energetic compared to Push-Pulls.  

Actually what is happening is how the SET makes distortion. The energetic quality is due to higher ordered harmonics showing up on the transients when you ask the amp to make any significant power. Those higher orders are interpreted by the ear as 'louder' although if you were to use a sound level pressure meter, you'd find that its an illusion. They are a sign that the speaker isn't efficient enough to take advantage of the better properties of the amp. Any time you ask an SET to make more than about 20-25% of full power these higher ordered harmonics are in the mix.

What Atmasphere is exactly what we experienced in our comparisons. Takes a bit of time to figure this out, but all 5 of the participants eventually came to the same conclusion. 2 of us heard this within moments.