Bifwynne, Your summation of Ralph's paper is pretty much synonymous with what I last posted. In general (a very important qualifier), don't try to drive a 4-ohm speaker with a tube amplifier, unless it is one humongous beast. Especially don't mate an OTL with a nominal 4-ohm speaker. The reason many/most of us (well, not me) are using multi-driver 4-ohm speakers is because they were made possible by the advent of high power SS amplifiers that use gobs of negative feedback to achieve a very low output impedance, necessary to drive a low impedance speaker, and great looking distortion measurements under laboratory conditions. The 70s phenomenon of the hi-power SS amplifier, abetted by the audio magazine industry, started this ball rolling. (Are any of you old enough to remember HP drooling over the Phase Linear 700 amplifier? 700W per channel, THD in the millionths of a percent, blew up on the odd occasion, sound like shit.) You may notice that more sensible speakers are making a small comeback in the market place, e.g., those made by Coincident, Devore, Spendor, and several others, possibly because there are guys with 10W 300B amps that want to listen to them. But the other point of my post is that Raul made an argument pro SS almost entirely on this issue of impedance matching, and it IS an issue with modern speakers but not the only issue to consider when selecting an amp to drive your beloved speakers. In other areas, SS amplifiers have faults not shared by tube amplifiers, e.g., sensitivity to a reactive load. Many SS designs cannot drive complex loads without becoming unstable, and many are generating much more distortion than a comparable tube amp under such conditions, when you're sitting there trying to listen to music. THD measurements are made driving a power resistor, hardly a surrogate for a modern loudspeaker with several capacitors in the crossover and inductive and capacitative drivers to boot. Also, don't be fooled by enormous "Damping Factor" numbers, another myth made live by the reviewers. Damping factor is the ratio between the input Z of the speaker and the output Z of the amplifier. Typically, the speaker value is assigned to be 8 ohms. All you need is a ratio of around 10. Much above that, excessive DF can have a negative sonic effect on bass reproduction. Yet, very high damping factor quotes, sometimes in the 1000s, are a bragging point for SS amplifiers, again parroted by reviewers.
Having said all that, I would be the first to admit that modern SS amplifiers are probably not so guilty of these sins, and the gap between tube and SS has narrowed. I am very interested in the First Watt amplifiers made by Nelson Pass and in the more expensive Pass Labs amps, though I have yet to get an audition of any. Look for SS amps that use no or very little NFB. Look for amps that have lowest distortion measurements at lowest power output, such that distortion increases linearly with power from less than one Watt upwards. The first Watt is the most important Watt. Look for Class A SS amps. Those will be the best sounding, I think.
I think Raul is very sincere. But I, like some others here, go for "I like it". I like it, because I just came back from listening to live music and what I want to hear in my home is something that sounds like what I just heard from a live musician, with the same dynamic range and clarity. For me this hobby should be mostly a pleasure. I happen to think that when I get a glimpse of Nirvana, the system is doing most things correctly. The better it gets, the more of my LPs sound great. Every time I make a change in my electronics designed to reduce distortion, the system sounds a little better. Isn't that a sign that Raul and I are after the same thing but by different methods? Maybe.
