Can 10W 300B tube amp drive Martin Logan Ascent i?

You`re looking at a disappointing result with this match. This speaker is far too inefficient to work with your amplifier.Low watt SET amps can sound marvelous but only with appropriate speaker compatability.You have to avoid these types of power hungry speakers.

Franz456,
The choice of output tube is just simply subjective, there`re too many variables that affect preference. You could have two amps with the same output tube and they could sound radically different.I`ve owned el34,6550/kt88 amps and the best of each breed can be excellent.

My personal favorite type tubes are the DHT(directly heated triode) . When done right the DHT as SET or push-pull has a bit more 'naturalness' and realism of actual instruments and voice(at least to my ears). But that``s just one opinion among many other preferences.The bottom line is the amplifier and speaker have to match properly,thus many different tubes can work in the right situation. For example my speaker is 94db and a 14 ohm load(minimum 10 ohm) this is a wonderful match with my 8 watt 300b amplifier.
Regards,

John makes a good point. With higher sensitivity-higher ohm(load) speakers amp quality matters more than amp power watts. I have a very good push-pull amplifier(100 watt ultra linear and 60 watts in triode mode). The PP amp has a bit more bass weight and impact(not dramatic). In all other areas the 8 watt 300b SET is the better more realistic and natural amplifier.It just sounds more like the real thing in your room.

Franz, I believe the 50 watt amp is a much better choice for your Magnaplanars than the low power SET amplifiers. 4 ohm load and mid 80s efficiency just not a good match for this type of SET amplifier.
Regards,