Originally Posted by kevin gilmore
Any class A amplifier is only class A up to a specific power level.
That power level may vary due to the load. It could be 10mw
it could be 100mw. This is not specified. No one has bothered to
ask either. Even the largest krell amplifier ever made will fall into
A/B operation at some point.
Originally Posted by rickcr42
then it is not "pure" class A.you can have degrees of class A operation but if you are claiming pure class A the operating points are consitant,non varying until you hit clipping.then it matters not what class you are running as you are out of steam anyway and it will sound like crap.
I defy anyone to prove to me and back it up with measured results where a Szekeres Amp EVER goes out of classs A up to full clipping.That my freinds is what PURE CLASS A IS !
You can bias for class a up to a pre specified level and have an amp switch over to class A/B by design but that does not make the amp a Class A amp.
You're both right, if you're describing a single-ended amplifier, which, I believe, is what the amplifier in question is supposed to be. Crank up the volume on a single-ended amplifier and at some point, the plate current will hit zero and it won't be in Class A anymore. It'll be clipping, certainly, and that's what Mikhail pointed out in the original post in this thread. That's no different than any other single-ended Class A amplifier.
Kevin's post is a perfect example of a push-pull amplifier. Run it up so far and the plates will stop conducting and it will go from Class A into Class AB mode.
An amplifier is operating in Class A mode if the plate current is flowing in all output devices for a full 360 degrees of a signal cycle. So the Krell can operate in Class A up to a point, where half of the devices are in cutoff and the other half are in saturation, then it's in Class AB. In the single ended example, once the amp hits cutoff, it's technically in Class AB, but, since it's clipping, that's sort of a useless point.