why does triod mode sound better than ultralinear?

Can someone give us the basic circuit design differences and theory behind ultra-linear and triode? I have heard the two and it is clearly a trade off, but what I do not know is the circuit operation and how it directly affects what I am hearing. (clearly tube amplification is not my area of expertise--but I do enjoy dabbling in tubes).

Thanks for the info... Most of my question is just because I'm a EE geek and new to tubes. I to am interested in the circuit design. I have ProAc Tabletts which I think are somewhere in the 87 db range. I use these with a HGS-10 subwoofer which is not some peoples favorite but it's size solved a huge placement issue for me. I love the sound of this amp in ultralinear but I just gots to know....

The "ultra-linear" configuration was developed by Mullard to sell their EL34 pentode. It generally differs from a typical SET in that the SET usually has two tubes per channel - driver (eg 6SN7, 6922) and output (eg 2A3, 45, 300b). An ul amp will usually have four tubes per channel - an input pentode (EF86), a triode phase splitter (ECC83) and two output EL34 tubes - and it splits the signal. This is a push-pull type confuration whereas the SET is a straight-thru amplifier. The difference is that the SET sees fewer signal manipulation than the ul, similar to Class A transistor vs Class A/B push-pull ss amps. The "ultra-linear" name does not describe signal linearity but instead describes the way the EL34's are connected to the transformer (both the anode and the screen grid are connected - to stabilize the whole setup).

The trade off is power for the signal linearity of the SET (I agree with Marakanetz, SET signal path is usually shorter). Of course, it does not mean one is better than the other - there are excellent ultra-linear designs (Mullard 5-20) that can give the best of both worlds.

Btrvalik -- as you are driving Tablettes, I wouldn't change to triode if I were you. Tablettes are not very sensitive (as you note) &, if I remember correctly, they're not the easiest of loads...

I posed a similar question to the folks at Rogue Audio concerning the set up of my Rogue Audio Magnum 88 amp. Here is the response I received, "with speakers that tend toward the bright side, the triode mode may sound smoother and more natural.For speakers that tend to be laid back, UL may give it a bit more dynamics and or punch. It depends on the characteristics of the speaker".