What is the most powerful SET tube amplifier?

The Cary monoblocks noted 'informally' above are at http://www.caryaudio.com/cad1610se.html

Note that both the Cary and Bel Canto are driving their 845s into Class AB to get those power outputs, maybe even class B for the Cary. the 845 tube can only put out 27w in class A, at the bleeding edge (1250v), most are run at lower voltages. (1000v = about 22-23w in class A).

Fwiw,
-Ed

The most powerful SET amp I know of is the WAVAC HE-833, which is a 100 watt monoblock. That's almost twice the power of the Cary. At least one person is using this beast to drive his Sound Labs, which means the amp is quite capable of driving a very difficult load. The price is in the same ballpark as the Cary. Replacement 833 monster output tubes are quite reasonable - around $250 each last time I checked.

Here is the address of WAVAC's HE-833 page: http://www.wavac-audio.gr.jp/he833_e.html

The Cary (and presumeably the Bel Canto) drive the output tube grid into class A2 which significantly increases grid current and distortion. However, it isn't intended to stay in this mode of operation except for extreme dynamic peaks. Normal operation is class A up to around 25 watts as Ed pointed out.
Along with WAVAC, Legend Audio also makes an amp using the 833 tube with at least 100 watts (possibly 200?), but I don't know if it is actually a product or just a statement item. Wyetech has 45 watt SET mono-blocks, though they use two complete amp channels in parallel to produce this kind of power. Also, the company deHavilland makes a SET mono-block with the Russian GM70 tube that is a solid 30 watt.
Of course, there are those who feel that anything over 10 watts SET requires too many sonic compromises, but this will force the use of very efficient speakers. Hope this helps.

another set amp 100watts is siltech