My speakers are 97 db (Classic Audio Loudspeakers T-3) and I find 30 watts to be about the minimum, but I like to listen at higher volume levels (95db peaks).
A 45-based SET makes about 1 watt. You will have about 10% distortion at that power level, IOW you will not be hearing what the amp really can do- you need a speaker about 10 db more efficient than that (104db)! If you drive SETs hard, the qualities that they are known for will not manifest. A 2A3-based SET will only make about 3-4 watts, so you will still be limited by the power levels. Now if you had a P-P 2A3, then you would be making about 15 watts, enough to make things more life-like.
A 45-based SET makes about 1 watt. You will have about 10% distortion at that power level, IOW you will not be hearing what the amp really can do- you need a speaker about 10 db more efficient than that (104db)! If you drive SETs hard, the qualities that they are known for will not manifest. A 2A3-based SET will only make about 3-4 watts, so you will still be limited by the power levels. Now if you had a P-P 2A3, then you would be making about 15 watts, enough to make things more life-like.