Most 300b amps are good for about 7 watts.
The distortion goes up and begins to include the odd ordered harmonics at powers over about 20-25%. So you might have about 2-3 watts of really usable power- over that, you don't really get to experience what the amp is all about (despite many remonstrations you may hear to the contrary; keep in mind that many people with SETs often put them on speakers that lack the efficiency needed; this is **the most** common mistake made with SETs)!
So I would not consider any loudspeaker that does not involve either a high efficiency full range driver (like a Lowther or Feasterex) or horns. The exception would be if you are in a very small room or only doing near field listening. In most average rooms, you will want a speaker that is **at least** 98 db 1watt/1 meter.
The distortion goes up and begins to include the odd ordered harmonics at powers over about 20-25%. So you might have about 2-3 watts of really usable power- over that, you don't really get to experience what the amp is all about (despite many remonstrations you may hear to the contrary; keep in mind that many people with SETs often put them on speakers that lack the efficiency needed; this is **the most** common mistake made with SETs)!
So I would not consider any loudspeaker that does not involve either a high efficiency full range driver (like a Lowther or Feasterex) or horns. The exception would be if you are in a very small room or only doing near field listening. In most average rooms, you will want a speaker that is **at least** 98 db 1watt/1 meter.