What Sensitivity with Tube Components?


Hey,
I am interested in upgrading from 100 watt Solid State to Tube components. I've been told that my 89db (sensitivity) B&W speakers will not work all that well with tubes and that at best, speakers should have at least a 90-91db sensitivity to used with tubes.
Any comments or suggestions regarding this question? Thanks.
wcc10
Thanks for the replies,
B&W CM6s speakers (for now)
Speakers situated on solid bookcase/cabinet about 7 feet apart right to left. Listening position about 7 feet from speaker position. I listen loud enough to hear it! (no distortion!!)
Room is about 24x24 feet with banks of windows on two sides.

Listen to a lot of Blues/Adult Rock, some Jazz and some Classical.

Look forward to any suggestions.

24 x 24 room - nice....
On a bookcase - against the wall ? 
are one or both speakers along one bank of windows ?
CM6s2 ?  like these 

http://www.u-audio.com/shopimages/gmosp156/0000000045302.jpg

what are you looking to improve upon and whats the current amp? 




About 6 inches from rear wall both speaker have clear field horizontally. Windows are about 3-5 feet from speakers.
Current Amp/Receiver is Yamaha R-S700.
Yes, speakers like those.
I have decent cables but system sound "bright" to me. Granted, there is room for improvement all the way around. Looking for more "warmth."
You can see, this is a "budget" system compared to many. I'm open to suggestions.
Those speakers are extra hard to drive - inefficient - due to the small box and B&W trying to make more bass with it.

B&W Manual
88dB spl (2.83V, 1m) its not a straight 88db spl (1.00v, 1m) comparison.
So they are actually worse.
Do the windows have curtains ? if so have you tried closing them.
The manual also says they need to be at least .5 meters 1.6 feet from the back wall and side walls.
A Big TV between them makes it worse too - not sure if that is the case. 

Your amp makes 100 watts at 8 ohms. and only 120 watts at 6 ohms. Your speakers go down to 3 ohms to make their bass.
The speakers are making your amp struggle imo with the bass. This throws off the tonal balance. Makes the speaker therefore sound bright.

If you buy a SS amp make sure the specs show doubling going down - 100 wpc 8 ohms, 200 wpc 4 ohms.
if you buy a tube amp makes sure it has 4 ohm connectors on the back.
I would go with as many watts as you can afford which ever way you decide to go.
important.
try to bring the amp home for trial. if you can't do that bring your speakers to the store and listen there set up as close as possible to your home.

my 2 cents.
All makes sense but you are saying that these speakers should be connected to a 4 ohm output? The Yamaha R-S700 has an impedance switch on the rear which allows for 4-8 ohm speaker set ups, bi-wire & not. (see page 13 manual)
I have not tried this setting in the "Low" (4 ohm) setting but maybe it would be worth a try?
Also, These speaker are at least 1.5 fee from the rear wall but I've always felt speaker stands would help. (The wife is not into this as much as I am) So on the built in book case the remain!
As for tube, you suggest as many watts as I could afford. You can buy a Jolida 100 watt Tube for under $2,500.00. So price does not always seem to dictate great sound.
Do I consider Class A, B, AB Tube amplification?
Thanks.