You have got to be kidding me right? You are not actually going to try
and use this for a reference.

I'd be interested in hearing what your objection is to this article. The
measured differences bteween the two amplifiers were certainly large
enough
that they should have sounded different.

The discussion has been about solid-state amplifiers. This was a tube vs.
SS experiment.

In any case, your 2AFC test appears valid. The presence of the
potentiometer for one amplifier but not the other is rather troublesome (I'd
use pots for both amps).

How did you ensure that the amplifiers were operating within their linear
range?

In addition, did you measure the "important" parameters of the amplifier
before or after the test? I didn't see any mention of distortion, noise,
frequency response, etc measurements. This is rather important, because
noise issues, for instance, could have been prevalent and in fact could have
been the sole determining factor for the listeners. The source of noise
would then have to be identified. If the differences for the two amps
tested were indeed significant, then it would have to be determined if the
noise parameters of the amplifiers were typical.

As an aside, in car audio we're less concerned with noise than in home
audio. We're battling all kinds of noise from the getgo. So, even noise
levels that are considered mediocre in the realm of home audio are well
above necessary for us. The noise floor is incredibly high. This of course
is an important consideration when trying to compare the two environments.

As for the results:

Your 64%-38% "difference" vs. "sameness" comparison is essentially worthless
due to what appears to be a bias in the responses in favor of "different".

Your primary group data analysis with the 52% number didn't show any
statistical measure of confidence. Either that, or I overlooked it. Do you
have that data available?