SET for Orchestral , Big Band etc.

The magic one gets from SET amps is achieved usually with high-efficiency speakers that can generate high SPLs at low power inputs. What's the sensitivity of your new speakers?

If you don't need ear-damaging peak levels, one can use a lower-sensitivity speaker, but that combo still needs more power than the flea-powered (ie 2A2, 845, 300B) SETs can produce. Until I fell in love with a pair of Eminent Technology 8s, I used 50-Watt 805-based SETs, Antique Sound Lab Exp. 805s, with 86dB-sensitivity Quad 989s in a fairly large (c. 3200CF) room. Peak SPLs tolerated by my ears is c. 95dBA, and that combo satisfied that. I ran them full range--no filtering and no subwoofers--and the combo sounded excellent. See Art Dudley's review of the ASL 805 in 'Stereophile' here http://www.stereophile.com/amplificationreviews/304antique/index.html . The 805s proved to be a few dB underpowered for the ET8s so I'm now using Quicksilver V4s.

My significantly improved pair of 805s is for sale.
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What speakers are you going to get?

Provided you have highly efficient speakers with a reasonably high minimum impedence (95 db.+ efficiency and minimum 6 Ohm impedence), a very well built single-ended amp that puts out 15+ watts/channel will generate high sound pressure levels. You will likely not have the bass tightness you want, however, as single-ended amps have little damping (unfortunately, you have to spend a ton of money to get a single-ended tube amp with the kind of output transformers and power supplies that will really control a speaker -- think Wavac or Lamm).

Will such a combination do justice to full-blown orchestral? It will be about as deficient as 99.9% of the standard (non-single ended) high-end stereos out there, meaning that it will sound pretty decent, but poop out when the going gets rough and also obscure the instruments and voices (very few stereos can realistically reproduce eighty people arrayed on a stage, playing instruments together).

Someone is selling a pair of Coincident Total Victory II's right now in the Audiogon classifieds. This is one of only a handful of non-horn type speakers that is full-range and built for low output single-ended tube amps, and will get you about as close to orchestral music with a single-ended amp as anything will (each speaker has eleven drivers -- they can go really loud, cleanly). The Coincidents are very well built, too. Here is the link to the ad:

http://cls.audiogon.com/cgi-bin/cls.pl?spkrfull&1134675623

to my ears the 300b is a bit too lush for orchestra, but then again, i own and 845 so i may be biased. to me everythihng is subjective

Depends on design as regards the sound of a 300B amp. But as everyone knows, the speakers must be an easy load - higher and steady impendance (6+ min. without going much over 11-12 ohms), efficient (87db at least), and an easy phase angle through the crossover (which also contributes to impedance). Get these three things in a speaker (plus musicality) and the 300B should put an orchestra in your room. I use a room of almost the same size, 11 x 13.5 x 8, and currently use an Air Tight 300B to damn good effect.