The speaker/amplification wars continue

Triode mode can not produce slam when needed, as in Elliott Carter vocal work, Whats Next operetta.

Yes, you need enough power and this is probably true of your amps but not of all triode amps :)


But if you have enough power from a triode amp there isn't any going back to pentodes. Of course, triode power is more expensive than pentode (pentodes trade off linearity for more power) which is why higher efficiency speakers are useful!

I would guess each has tube has their pluses over the other.

That is correct. Triodes makes less power but are more linear (allowing them to sound better). Pentodes wired in triode (that switch to which you referred) aren't the same thing! Triode P-P amps are available in a variety of power levels.

ith respect to tube types in pushpull amps, I tend to like 6L6, KT66, EL34, and EL84 tubes over the likes of 6550, KT88, KT120 and KT150 tubes.

You might consider what push pull *triode* amps can do. Triodes are a lot more linear than pentodes and tetrodes.

@mozartfan While I am also a fan of easy to drive speakers, regardless of your conclusion I really should point something out. The Defy 7 is a rather large amplifier and a 211 SET is not. In a nutshell if you want to know how PP does against SET, to start with maybe both amps should be the same power!

Another way to look at this is if you really want to know the difference between the two, how about eliminate some variables, like make sure both amps in the comparison use the same output tubes at least.

If you want to know weaknesses of SETs here are a few:

1) Because SETs make about 10% distortion at full power, if you really want to hear what they can do the amp should be driving a speaker that is efficient enough that the amp **never** makes more than about 20% of full power. This prevents the higher ordered harmonics from becoming audible; if they become audible it will be perceived as 'dynamics'. IOW the 'dynamic' character of SETs is caused by distortion and nothing else.

2) Obviously the speaker choice must be done carefully as outlined above. The output impedance of any SET is fairly high and the amp does not act as a voltage source, so your speaker choices are limited.


3) The higher the power of the SET the more its bandwidth is limited by the output transformer. This is true of PP too, but isn't really a problem until you are making over about 100 watts, as opposed to about 6 or7 with an SET. This is why the lower powered SETs like the 45s are preferred, but a 45 can only make 0.75 watts!

4) One advantage of SETs is that as you decrease the power the distortion goes down to the point that its unmeasurable. Distortion obscures detail; this is the source of the 'inner detail' that read about in so many SET reviews. But this property isn't limited to SETs, there are a number of PP amplifier topologies that allow this as well. 


5) You'd think an SET would have the simplest signal path but that isn't always the case. There are amplifier designs that have only 1 gain stage; SETs have 2 or 3. In an SET distortion is compounded from one stage of gain to the next in the amplifier. If you have a PP design and in particular if that design is fully balanced from input to output, you can cancel even ordered harmonics in each stage as the signal progresses through the amp. This results in dramatically lower distortion (smoother sound with more detail) even if feedback is not used.

I've yet to see a situation where an SET could sound better than a PP amp **when the variables are more controlled**. Its very safe to say its an antiquated technology which has been sidelined by succeeding arts.