Switchable Tetrode - Triode please explain

I am using a VTL ST-150 which is switchable from 175 watts tetrode to 80 watts triode . Can anyone please explain the pluses and minuses of these two modes ? Thanks!
It's all inside the tube logic:

Tetrode mode is needed when the dynamic music needs to be reproduced: large orchestras, brass bands and has certainly larger gain than triode.

When the triode mode is used when you need maximum transparency listening to the small instrumental bands, vocals.

Also VTLs having that switchable feature can be used to match different types of speakers depending on their efficiency.

Do not forget to turn it completely off before switching modes!!
The tetrode tends to give the music a more forceful, forward presentation. It also has more dynamics and deeper bass in Tetrode. Triode, on the other hand, may be a bit more laid back and at first may not seem as seem as appealing. Give it a chance. I have been spending a fair amount of time listening to small jazz ensambles and acoustic blues in triode and the sence of realism and of "being there" cannot be matched by the tetrode mode. Acoustic instruments are 3-d and the vocals seem a lot more real. I also get a better sence of the room environment the recording was made in in triode. Triode also works well with string quartets....basically acoustic music in general. The dynamics in triode mode won't take you by storm but if you are critically listening the triode should bring a smile to your face with the less dynamic music. I've left it in triode for some large rock band CDs and it fared well there. As far as using it to match speakers with the amp, i'm not too sure about that. Its an apple and oranges thing. The two different modes produce a different feel to the music as a result of how the tubes work and the amount of power produced. Since triode produces less power it may not work as well with low efficiency speakers if you have a low power amp but if you have a pair of Wotons i really don't think it would matter what speakers you used with what mode. I'm actually starting to think about the VTL 250 triodes. I have the VTL 185 signatures and the 5.5 pre-amp driving a pair of dunlavy athenas now. It's an easy audition so check it out but do power down first or you will fry some tubes (watched the guy at the local shop do just that).
Hi Weiserb; would you mind telling us what differences in sound quality/character you've noted when switching from tetrode to triode mode(s) with your amp? And maybe what speakers you're driving with it? I've been thinking of the VTL 150 myself. Thanks. Craig
why do you have to power down to switch? i can switch mine back and forth without missing a beat. triode is less rated power but i have found it to sound even more powerful than tetrode.
I agree with Kirk930. I have found that triode mode, even though it has less actual rated power, generally sounds more dynamic than a tetrode. It is similar to the way a 300B triode at 7W can sound more dynamic than a 35W push-pull.

I listen to mostly symphonic works and find my 7W Amp more than dynamic enough with my speakers (91db)

If I do not power down the amps I can hear and see how speaker drivers are poppin'.
just don't like to have my speaker blown. even when I place a cartridge needle on the groves I do mute my phono before.
The System I am using ...
CJ Premier 14
Linn Lp-12 with lingo , Grado
Sonic frontiers SFCD1
Aerial 10T 's

I listen to Pop rock , Jazz , Blues and Classic rock. I like to play mostly at concert levels !
I think the Tetrode mode produces more forceful bass and is a little more lively. Powering down as per VTL does make it more difficult to compare. I like the VTL amp very much! I just think the explaination of this issue on the VTL web site is weak.
I find myself about to write what Piezo described so I ditto his excellent description... I also find triode (I use VTL 450s) to be lush, exuding a luxuriant 'thereness' and beautiful instrument separation - particularly notable in massed strings, and choral works where individual voices both make up the group and somehow seek to escape it. On SACD, triode can be downright scary. I appreciate tetrode however for 'live' rock music played at 'concert' SPLs, where it seems to better convey the sense of being too close to the stage for one's own good. I used both modes evenly at first but use it in triode most of the time now - more shivers and stupid grins (though tetrode on music with BIG dynamics can leave me breathless).

Piezo, have you used a different preamp with your system? Do you find the 5.5 affects your choice of use of triode or tetrode? Would you recommend it (or another preamp)? I use a passive attenuator and wonder if that is one reason why I lean to triode so much...
I have used Manley Reference 200/100's for the last few years with either Maggie MG3A's or Stax F-81's; both wonderfull combinations in most respects. Luckily, I don't listen at particularly loud levels so this dilemna is tolerable: In triode mode both these power hungry speakers benefit from a much more refined presentation as far as timbre and microdynamics. Instruments seem a bit leaner, but with their harmonic structures much better preserved, and their leading edges more incisive in a natural way.The soundstage appears to be somewhat smaller, but the dimensions of it are far more obvious, and there is a lot less texture in the spaces between instruments. Microdynamics are actually more natural, although ultimate dynamic range is compressed. On those occasions when I feel like listening at louder than usual levels or the music is extremely complex and dynamic (big orchestral works and some rock) the music reaches a dynamic ceiling sooner than it should. Since on those times, I'm usually not doing serious listening (working out or running around the house), switching to tetrode is the ticket. I can play the system at louder levels without obvious compression, and although I find that the sound, in general, gets a bit thicker than life with less harmonic detail, the increase in bass drive makes up for it. I am always reminded of when I switch between my Vandenhul MC and my Grado. Overall, I much prefer triode mode.

By the way, from Evana Manley herself: "You can switch between the two modes without powering down, but MAKE SURE THAT YOU MUTE YOUR PREAMP FIRST!"

Hope this helps and Happy New Year.