What is the characteristic of diff. Triode Tubes?

Disclaimer: Just trying to help so be aware that this is very subjective and I've only been into tubes for about a year with limited experience.

Matching an amp (with various tubes) to a speaker with the appropriate sensitivity and characteristics is, I expect, an art and only comes with experience but here are some starting points that I found useful.

TUBE - AMP - POWER - SPKR - "SOUND"
2A3 - SET - 3.5 watts - 93dB - magic; refined
300B - SET - 7 watts - 90dB - magic; clear/natural
KT88/triode - P/P - 15 watts - 88dB - warm; solid
KT88/pentode - P/P - 25 watts - 86dB - ?
(P/P = push/pull design)

I started with ASL Wave 8 monoblocs (P/P) which are a great place to start (bang for buck and they're resellable). I tried KT88s in the AES Super Amp (P/P) and liked that better (Svetlanas were my favorite). I then got an AES SE-1 (SET) that can use either 2A3s or 300Bs. I liked the Sovtek 2A3s better than the 300Bs that came with the unit. Then I tried Sophia 300Bs (300/pr) and have found the sound I was looking for. Since the speakers I use have a sensitivity of 89dB, is reputed to be tube friendly, and I listen at moderate levels, the 300B has been a good match.

The main point I'd make is that I have enjoyed owning all three of these amps (and they satisfied my curiosity about these tubes you are asking about). Listen if you can to amp/speaker combinations before buying, but if you cannot (like me living in the sticks) stay with amps in your price range that have a good resale value here on Audiogon and enjoy.

I am confused a bit.. so is the ASL MGSi15 DT integrated amp (http://www.divertech.com/mgsi15dt.html) a SET amp or not? Looks to me like it is a SET in a triode mode and not if it's in another mode. Please correct me if I am wrong.

ake

Sorry for the confusion. I was referring to the AES Super Amp that I owned that was a push/pull design. It had 15w/ch in triode mode with KT88s. According to Divertech, the ASL MGSi15 DT is a SET design with KT88s. I have not heard that so I was trying to relate the KT88 sound that I had with my AES. The ASL will no doubt sound different using a SET design (hopefully have some SET magic).

I took another closer look at the Divertech site.
The ASL MGSi15 when running in triode mode is only 5w/ch. The 15w/ch is for pentode mode. If you want to use it in triode mode, you'll need fairly efficient speakers (say 92dB/w sensitivity) if you want more than polite levels. I'ver read some reviews that suggest pentode mode gives tighter bass but is not as refined as the triode mode (I never ran mine in pentode mode since it required an internal wiring change on the AES).

Before delving into the subjective differences in the three named tubes it might benefit us to answer the first question which is what are the characteristics of the three tubes. The 300B and 2A3 are true triodes or three element tubes, without getting too technical they consist of a cathode, a plate and a control grid between the two. When operated single ended the inherent distortion signature of these tubes is that distortion, although high, diminishes linearly as the harmonics of the fundamental increase. The KT-88 is a different beast. It is a beam power tube. A beam power tube is a pentode or five element tube; the elements are the cathode, control grid, screen grid, plate and supressor grid. The additional elements are used to collect and concentrate stray electrons flowing from the cathode to the plate into beams thus substantially increasing efficiency but, some would say, adversely affecting the distortion spectra of the tube. Such a tube, the 6550 is a similar power tube, can be operated without using the additional elements and then can be said to be a pentode tube operating as a triode. One problem with this is that the additional elements are still in the physical envelope of the tube and certainly affect the path of the electrodes from cathode to plate and are two more elements to resonate causing distortion. Although many would argue that the the distortion spectra of a pentode is subjectively improved by only connecting the three elements many also believe the the distortion spectra is still several orders of magnatude less consonant with the musical structure than true triodes.