***SET***What Is Your Experience With Different Flavors***

@jond you can keep design, execution, output transformers, power supplies, etc. the same, and simply run different tubes - 45, 2A3, and 300B, for example, to hear the differences in tube types.  Yes, they may use different filament voltages, but using a power transformer that can accommodate it provides the solution.

In an SET, the 300B makes the most sense.  The other tubes just don't make the kind of power to drive even the typical high efficiency loudspeaker.  Larger triodes, tetrode and pentodes can also do well when used as triodes, but triode tubes of the previously listed ilk, including the 6AS7 Ralph's amplifiers employ, normally make the best sounding amplifiers.

If the product uses a push-pull configuration in a traditional transformer coupled amplifier, the number of loudspeakers it can suitably drive increases most significantly.  I feel the 2A3 can drive most typical loudspeakers, and sonically outshines the 300B in these cases.  The 45 may sound even better, but as it still only puts out about 5 watts in this configuration, it's still limited in what you can pair with it.  Obviously, Ralph's amplifiers use the 6AS7 for logical reasons, and to very good effect

+ 2 to me it's less about tube type or topology and more about design, execution, output transformer, and power supply quality. I had well regarded 300B monos I didn't care for, I have an EL34 triode wired Class A pushpull amp that sounds fantastic.

^^ +1

Speaker matching is pretty important, as a general rule of thumb the speaker should have enough efficiency so that the amp never makes more than about 20% of full power. This is so if you want to really hear what the amp is about.

With SETs the smaller the amp, the better. This is because it is very hard to get bandwidth with single-ended output transformers. Initially, the 300b was king; by the late 90s the 2A3 took ascendancy; now days the 45 is highly revered.

I have heard "real" triodes (300B) and pentodes wired in triode (EL34) both sounding great and both sounding poor.  It is very hard to generalize as many factors come into play such as negative feedback, circuit design, power supply, capacitors etc etc. 

Notwithstanding the above, I have had more success with true single ended triode tube amplifiers paired with a correct speaker sounding the best.