Speaker noise - hissing

50 watt power amp and tube pre-amp. I hear the noise when source is off as well as pre-amp being off. Maybe it's just time to replace the output tubes? ... 6SN7GT x 4.

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.

Newbee, The amp is an Audio Aero Capitole. It has four 6SN7GT tubes, four E34L tubes and four 6550C tubes. No loss in clarity just the hiss.

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! :-)

The noise is new...same amp and same speakers. I can hear the hiss from 3-4 ft but, not really from my listening position of 9-10 ft.