going to tubes, just one question..

Great move. I think you have basically 2 choices in your set up depending on your musical tastes.If you value the immediate and intimate sound of smooth club type jazz, vocal presence, chamber or light orchestral works, you may want to pair a SET amp or low powered Triode type amp with anywhere from a few watts on up. Triode amps in the 15-25 W range are nice here and are usually less expensive generally than the low powered SET amps both in purchase cost and re-tube costs. The key will be a highly effecient speaker of which sensitivity should be at least 91 db at 8 ohms.
The other approach would be to play it safe and opt for a high power tube amp sufficient to drive both effecient and low impedence load speakers to satisfactory levels. You have many more options here of course both with amps, speakers, and musical preferences. The big down side here can be cost, but you still have a plethera of good amps of excellent quality to choose from. Too many to name, but 100-150W ch. with tubes can be very nice with all but the most ineffecient, low impedence speakers. Best!-Ken:)

Ditto Kehut!

My advice would be to plan purchase of amp/speakers together or have a plan you can follow through on if buying one now & the other later.

A quality push/pull class A 300b amplifier putting out 18 to 20 watts will drive most speakers just fine and sound very, very good; the Sun Audio unit of this design if very good. A quality EL34 based push/pull class A amp might be a better choice to start with as they make around 35 watts and sound very good.

The fellow that just placed an ad on audiogon offering to build custom 300b amplifiers will also build other types. I have listened to his personal 300b amplifier; it is as good as anything I've heard and I've auditioned vintage Kondo Shinri, Kassai, Ongaku and the current Kondo Neiro amplifiers. Alex could build you a lovely EL34 amp for well under 2k and a spectacular push/pull 300b amp (with a power supply that will handle anything) for around 3000 to 4000. Apparently the more power they make the more expensive they are as the parts required get more expensive!

One piece of advice for a potential new tube system owner: be sure you have a reasonably well ventilated room. A tube preamp and class A tube amplifier will generate enough heat to increase the ambient temperature at least ten degrees. That is just a guess but I know my room gets damned hot and I even take the tube amp (SET 300b) out of service on very hot days and use a solid state Bryston 2B in its place (only a few days per year).

There are more than a few high efficiency speakers available, too, so that should not stop you from a single ended 300b amp putting out 8 watts. My speakers are 96db and 8 ohms; my 8 watts plays plenty loud and with plenty of dynamics. They are Galante Rhapsody speakers and they go for 1100 to 1300/pr used. Other possibilities are the Bag end MM8, Klipsch RB5, Omega Grande 6 and Grande 8, Galante, and others. I only mention moniter speakers; if you have room for floor standing speakers there are plenty of high efficiency speakers available.

FWIW power ratings can be misleading. My Audio Note Soro (SET) is rated at 18 watts and can drive my 88db speakers to near all they can handle. The Soro sounds like it has closer to 80 watts and very vibrant and flowing it is, the music flies out of the speakers.

Speaker impedance is usually the issue with tube amps, they usually do not like to go down to 4 OHMS. This can be helped with an autoformer like Paul Speltz sells at zeroimpedance.com. You replace your speaker wires with them and can increase the impedance load the amp sees depending on which wire you use. You can fine tune the sound to tighten up the bass as much as you want, they are fun and very good.

Just my 2 cents

Spearker impedence (as indicated by posts above) is very important, not only nominal impedence but minimum impedence, as well as a fairly flat impedence curve. The output impedence of the amp is also important as well and should be as low as possible. When I last shopped speakers for tubes I settled on a speaker which had a minimum of 5ohm and nominal 8ohm rating and a fairly flat curve. Even though its efficiency is only 86dba I drive can drive it to very high levels (for a medium sized room) with only 80wts from a PP amp. It is all about proper matching of the speakers and the amp.