Hi Alan,
I think it's a good idea to stay focused on one thing at a time. High powered single ended amplifiers are notoriously difficult to get right, and I think probably it's easier and more cost effective to begin with a push-pull design. Incidentally, class A push pull can also perform well, you could change your existing design to full Class A without even losing much power, and then sleep better at night. I've certainly never looked into the theoretical operation of tubes in class AB with this level of scrutiny, but the questions you're asking do make sense. I do look forward to seeing how they're eventually answered.
Over the holidays I decided to change the capacitors on one of my amplifiers which happens to be class A push-pull, with 807s (similar to 6L6) and I put them into my system a few days ago. It's nice to have the high power reserve, and I can't really say for certain it sounds worse than my single ended amplifier.
-Max
At this point, I think I am right about the gain match ONLY if the internal plate resistance is 0ohm. Take a look at post #19, the higher the plate resistance, the more it is mismatch.
I gave it a lot of thoughts on post #19 to use equivalent circuits to simulate the 3 conditions.
I know people think this is a waste of time to dig so deep into the theory, much easier just build and listen. I just disagree with this idea. I believe digging down as deep as possible gives a lot of insight to the advantage and pitfall of a design. Really understanding the circuit is the key to a good design. One needs to start with a good sounded foundation. This, I am surprised after like two months of studying tubes, that people in tubes just don't go deep into theory. At this point, I really read ( at least scanned through a lot of books and articles), there are HOLES in the the theories, big holes. It's just too bad there are so few people that are interested in tubes these days that nobody actually stop and spend the time to look deeper and cover the holes from the theories of the 40s and 50s.
I know this might be offensive to some people, but I can only say one can never get away in the modern SS world. Everything is analyzed and understood in SS power amp design. Every circuit has explanation WHY it is what it is. I really believe if people would stop and give the same scrutiny to the tube theory, there are room for improvement. It is not about "tubes has so much distortion, that the change are very graduate that you won't notice...". It's about knowing what's the short coming and make the best out of it.
Yes, I thought about that I can get more class A power using PP rather than SE also, it's true. It's just an alternative way of thinking. I am not worry about how difficult it is to implement the parallel tubes SE amp. This is where I really feel differently on this whole thing, and I feel quite strongly about this. Getting circuit to work, tame the circuit from oscillation is just a process. It'll get done one way or the other. It's just take the time to fix it to get it working according to the design. BUT if the foundation is wrong, there is nothing you can do to fix it. As for the implementation part, you just handle it. I am not going to say I can make the 3 tubes SE amp work nicely as I have not try it. But I have never failed in implementation in my years of career. I just handle it as it comes. There's a will, there's a way.
Case in point. I have not seen anyone design like my SS amp. Believe me, I read tons of schematics to make this statement, some in diyaudio came close but not close enough. I went for ultra low distortion, I maximize the forward gain to the extreme by maximizing the gain of each stage. You are talking about over 60dB feedback gain in audio band and bandwidth of over 330KHz. Nobody do this because it's so so hard to tame it from oscillation. I did it in 3 weeks. I tame it even with 20,000pF on the output connector of the amp. To put it in perspective, the famous Nelson Pass Stasis Nakamichi PA-7 BURSTED into wild oscillation with only 1500pF on the output connector. Getting it to work is just a process. Getting it right in theory is the harder and the most important part of the design.
Alan