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Tetrode vs Triode mode in Tube amps

Below is an explanation of tetrode vs triode mode in tube amps from the VTL website. I've never owned a tube amp before.....If they do not all have this switching ability, which mode do tube amps usually operate in generally speaking? Or is this an individual thing per user.
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VTL Tetrode-Triode Switching Capability

The VTL range of power amplifiers offer a unique feature that makes them even more flexible: On-the-spot switching between tetrode and triode modes of operation that is easy to reach and user switchable.

At lower volume levels, and with efficient speakers, the sound of the triode mode offers a level of delicacy, liquidity, and sweetness to vocals, chamber and jazz instrumental quartets and solo instruments with 3-D imaging in the mid-range that will get you even closer to the real event.

Tetrode mode offers the detail, soundstage width and depth, and weight to the music that on large-scale orchestral or big band will transport you to the concert hall with all the visceral power and detail rendition of your favorite music.

A changeover switch is provided on the back of the VTL amplifiers to make changing between the two modes a breeze - just power down the amplifiers, flip the switch to the desired mode, and power the amplifiers up again.
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marakanetz's avatar
marakanetz
5,473 posts
 
Dmoffitt,
It's quite opposite:
Tetrode has cleaner and more linear power.
Triode has sweeter midrange.
tlcklp280e
2 posts
 
I disagree about tetrode being "cleaner". No doubt that tetrode has an edge to it which triode doesn't, but I find that edge to be the grain associated with pentodes (or tetrodes) not true musical detail. Triode is indeed smoother and sweeter, but I find that its simple, pure sound to be more direct and cleaner, once the "razzle dazzle" tetrode grain has been eliminated.

With VTL I do prefer the bass in tetrode mode - seems like not enough feedback (my guess here) is available in triode mode (feedback drops when you throw the switch because the output tubes have less gain in triode mode)
eldartford
4,262 posts
 
What is a "Tetrode"? Is it a Pentode, with one grid not connected?

Anyway, in the "Ultralinear" design, the "extra" output tube grid is excited directly with the signal from a winding of the output transformer made for this purpose, and provides the simplest and most effective form of negative feedback around the output transformer. Output transformers are highly nonlinear and do not have flat frequency response, which is why you can't get much poiwer through them in triode mode. The Pentode connection lets you drive more power through the transformer before distortion becomes excessive. That's why Pentodes were invented.
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