Question about set amps and low sensitivity spkrs

Hi, In about 3 weeks I will take ownership of an 18wpc SET integrated. I currently run an Arcam SS amp with B&W 602 S2 speakers and I'm still undecided about new speakers (more sensitive, tube friendly) to mate with my new amp. My question is, can I run my current 90db sensitive B&W speakers with the SET integrated without doing damage, or shortening the life of my new tubes? I'd hate to have the amp sitting in a box waiting for me to decide on new speakers :) I frequently see that B&W speakers don't mate well with tubes...why is this?
Hi Michael,
One reason B&W speakers might not work well with SET tubes is not necessary the efficiency, rather that the impedance swings on B&W speakers in general are wide, a 8 ohm nominal speakers can be down to 4.6 ohms. And most SET do not like wide impedance swings.
I was using Cary 300SE signature (15W SET) driving B&W CDM1SE for a long time, extremely happy with the result, now granted, my listening room is small (11X14). I recently changed the speakers to ProAc Reference 8; love the ProAc mid-ranges.
So, all said and done, I think it really dependent on what type of music you generally listen to, and how big a listening area you have.
Good luck!
Many tube amps do not work well with B&W's (and a lot of other speakers) because of their impedence, both nominal and min/maximum, not because of their efficiency (so much). Optimally, tube amps like to see flat impedence curves about 8 ohms or higher. Speakers with dips below 4 ohms can be a problem and speakers with big swings in the curve as well can be a problem.

Speaker efficiency is not as important except as to volume potential. Actually 18w will give you some moderate sound levels in a modest sized room BUT you might no like the sound at all.

Your new amp will probably have 4ohm out put taps. Hock up to this, don't overdrive your speakers, and you'll damage nothing. BTW, be very careful in your selection of new speakers. Many folks advertise how their speakers are tube friendly when in fact they may not be at all.

Hope it all works out for you, you've taken a difficult approach to getting a good system(to your ears) by buying a small SET amp without having specific speakers to match it with. :-( IMHO of course.
I agree with both Mr N and mr T: You won't hurt the SET at all listening to your B&W's. You may even be surprised by the levels it can achieve(though I wouldn't get too ambitious). Just don't try to match the SPLs the Arcam delivered. It'll start to sound bad before you get that far anyway.
Thanks for all the informative, helpful responses, very much appreciated. Well, the amp has both 4 and 8 ohm taps...the speakers are rated at 8 ohm, so I would still use the 4? Or should I sue the 8 ohm amp taps? It's funny everyone tells me I'm going about this the wrong way, by buying the amp first! I just figured I could choose the amp I liked and try to match speakers to it, but this seems to be a beginners mistake! Thanks again!
No real mistake was made. You wanted, and found an SET amp. You already knew you'd need more efficient speakers to go with it. You'll be able to listen to what you have until you get the new speakers. As long as you are building your system based on accurate information, you'll achieve your goal, regardless of the purchasing order.
The short answer is yes you can use the SET with your B&W without doing damage (though your tubes will work harder than they would with a different speaker, but that isn't damge, just wearing out tube life), but the specs suggest a match far from ideal. Like others have said, the sensitivity per se is not too much of a problem at most listening levels, though measurements I saw in audioXpress suggest the real sensitivity is really closer to 88db. The real problem is that speaker has very large phase angles (large swings in impedance) which are not so hot for hot for SETs or tubes generally (why many B&W speakers don't always match well with many tube amps). So, you should be fine for now, but if you love the amp, you do need a different speaker to hear it at its best. With 18 watts I would look for 92db minimum and smooth 8ohm or higher impedance curves.
No harm in trying both 4 and 8 ohm taps and going with whichever ones sounds best. I have found 8ohm taps to sound better than 4 ohm taps with 4 ohm speakers- but it is a case by case basis.

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Having owned B & W loudspeakers before with similar sensitivity and impedence, 90db/watt and 4 ohm, I can say that mine craved a good deal of power. If mine were like yours this impedence value may drop to 3.6 ohms, as it was listed in the manual- NOT the sort of load I would want to pair with an SET.
Only problem with the 4ohm tap is that you are going to drop the wattage quite a bit - I think.
Do not forget Louis's Omega line of SET-friendly speakers. Outstanding!
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Tvad, I thought that was they way SS usually works, but not tubes (but I'm no expert).I know when I owned the RM10 Roger Modjeski said I would loose power if I used the 4 ohm tap versus the 8 ohm, but there were advantages in terms of dampening and distortion. By the way Mbleming, what amp are you using?
FWIW most tube amps put out the same wattage at 4 & 8 ohms. It neither doubles nor halves. 18w at 8 ohms is going to be 18w at 4 ohms.
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Thanks again guys, very much appreciated. As far as speakers go, I have been giving serious thought to the Devore Gibbons, but I'm still not sure. Thanks again!
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Newbee, I agree that a tube amp generally puts out the same power into different impedance loads of the speaker, but I'm talking about the output taps (4ohm, 8ohm etc.) of the amplifier. I thought that into the same loads, the 4ohm tap and the 8 ohm taps put out different power. That was my understanding with the Music Reference gear (I think he said a 3db drop using the 4ohm tap into a 8ohm load versus the 8 ohm tap); but I could be wrong.
Pubul57, Don't think so, but I've never owned or researched a MR amp. Nice stuff though.

FWIW the only thing I know of that halves power output of an amp, accross the bandwidth, is (for example) an amp which uses multiple types of power tubes and, say, is designed for max power from using 2 6550s/KT88's/KT90's per channel and putting out 80wts +/-, but the amp also allows for substitution of EL34s/6L6's. Putting in the EL34's etc will about halve the power output. Lest someone get anxious, this is not so with amps that are very conservative, such as Primaluna which doesn't seek max power from the principle tube, therefor doesn't reduce much more than a few watts when the smaller power tubes are used.