Speaker noise - hissing

Not to be picky but I assume you mean the small tubes in the power amp? That is a logical source of hiss. And 6SN7's are not power tubes.

From what you have said yes. Now if in addition to these small tubes you meant the big power tubes as well, if you've lost some clarity as well as having hiss, after you replace the small tubes it doesn't return, then yes the power tubes as well. One way to tell is to have a spare set on hand (a good idea in any event) and substitute them in and see if you hear a change. No change - take 'em out and check again next year.

Yes. Most probably the small tubes. If the hiss is annoying you will need to get 'low noise' tubes. They are usually a bit (or a lot) more expensive so be careful not to buy 'more' than you actually need. Also consider that changing tubes, unless you stick with the same brand, might well changes its sound a bit (or a lot).

OK.

Now, that I think about it, have you ever heard the amp operate dead quiet? Or is it a new amp to you and you are just noticing it. If you heard it operate dead quiet, was it with the same speakers or at least speakers with a high sensitivity level.

I ask for several reasons - one is that I don't know this amp (biggie) and of your speakers are high efficiency and the amp is new to you, you might just be hearing the amp's noise floor. But since noisy 6sn7's are not hard to find, perhaps/most likely that it the problem.

BTW, How far from the speakers can you hear this hiss? Can you hear it in your listening position? Or only when you put your ear next to the tweeter. If the latter, be happy! :-)

I'd bet it is the 6sn7's if it annoys you get some recommendations for some good low noise tubes. The new production EH's are quiet but I don't know if you would like them in your amp. I use them in some Cary amps and compared to some NOS RCA's I have they have a tad more edge, whereas the RCA's are a tad soft/mellow - depends how you look at it, and probably how they blend with your amp and the power tubes.

Rockyboy, When you changed out the tubes, did you replace the tubes with tubes tested for low noice? Lots of NOS, and new production tubes are not all that 'low noise' in demanding applications like your AA.