Triode vs. Pentode


I've been switching between Triode and Pentode modes on my VAC amp during the past week. This has been my first experimentation between the two. I'm having difficulty discerning a clear difference, and I'm enlisting the advice of you tube heads to explain what I should be listening for...

Thanks in advance!
tvad
Trelja, FWIW in my vocabulary smoother = less dynamic, but I didn't want to say something that would sound negative to many. But, as I said in my post, I think much has to do with the type of speakers you are going to be using as to whether or not triodes will make your day. I think I understand what you mean by clear, open, and detailed, but I get a little lost with the term "beautiful". Sonically speaking, just what does that mean? :-)
Newbee, it's probably just us seeing these goofy terms in different ways. I'll try my best to describe MY gibberish.

"Beautiful" is a sparkly (I know, no better) sound, where there is a lot of detail and air present, and everything takes on a shimmering tone. I can most easily equate this to brass and cymbals. They will have a tremendous amount of life to them, especially, in the decay of the note.

Smooth, means liquid and relaxed to me. Not necessarily going along with a loss of detail, but it often does. Now that I am typing this, I realize that it may well be the opposite of the shimmer I spoke of when I desribed beautiful above.

Triodes DEFINITELY have the shimmer going on for me, they have less of the "smooth" going on, but I in no way mean to say they are harsh or fatiguing, because they sound nothing of the sort. And, I don't want to say that pentode is smooth, as it is not more smooth, but that "shimmer" dissipates to a large degree. I know I probably sound like I am contradicting myself, but like that Supreme Court justice who knew pornography when he saw it...

Dynamic, to my own warped mind/ears is the ability to present the punch, the true stop/start of the musical event, and the yin and yang of the blackness of silence contrasted with the heat of the note's zenith.

Smooth can be dynamic, as exhibited by my new AtmaSphere amps, which are much more smooth, yet more dynamic than the older revision I also have. I A/Bd both on Saturday during the day and the evening, and the newer ones had great slam in the lower frequencies and were tremendously dynamic. Detail and clarity was outstanding. The older ones appeared more detailed, but a lot of listening more or less showed me that I was mistaking their forwardness for showing more detail and clarity - it was not so.

Neither, despite both being Class A triode amps, exhibits the "beautiful" sound that I was describing of triodes, which was a reflection of my Granite tube monos and other tube amps that I have been around which offered the ability to run either way. Obviously, despite these comments, I am still a tremendous fan of the Atmas, as in so many ways, I think they are the finest sounding amps made. It's more that a lot of tube amps can have a whole lot of sweetness, and it may or may not be always warranted.

Sweetness is another word that REALLY describes triode for me. Going to pentode seems to remove that sweetness, and adds a good measure of punch. Which do I prefer, definitely triode - presuming the speakers don't need more juice. In my own Granites, matched with my Coincidents, when running KT88s, I go for triode. With EL34, I need pentode, as triode doesn't pack enough wallop for me. Overall, KT88 in triode sounds best for me with these amps.

Tvad, you certainly have done a yeoman's job in assembling the system. While everything looks great on paper, I would first look into running CD direct, and secondarily, the speakers. As I said, I faced my own problem of this sort for a good, long time. At one point, two interconnects that I previously heard tremendous differences in showed none at all! It was probably just luck that I was able to work through it, but now I can hear quite meaningful differences in triode/pentode, cabling, CD players, etc.
Thanks for your thoughts, Trelja. I'm quite satisfied with the way the system sounds with the VAC in pentode mode, but I was/am curious to hear what triode could bring to the party. I think I'm going to stay put with my equipment at this stage. If I have an opportunity to audition a CD player with volume control, I'll certainly try CD direct to hear what differences that might entail.
To my ear, pentode gives me the impact on the head of the bass drum, while the triode pulls me into the middle of the tone. Pentode offers punch, while triode is seductive.

Just my 2 cent ears...
"Pentode" means that an extra grid in the output tube is being fed with a signal taken directly from the transformer secondary winding. This is "corrective" (negative) feedback for distortion generated by the output transformer. This is why the amp can deliver more power before distortion becomes excessive.

If you do not listen very loud, and your speakers are efficient, the power delivered in triode mode will be sufficient. Distortion will be higher than the same power in pentode mode, but the harmonics generated by tube amps are not unpleasant, and you may actually prefer the distorted sound.

So, the "best" mode probably depends on the kind of music you are listening to, and how loud you want to play it. Feel free to switch back and forth.