VTL Tetrode/Triode

What are your speakers/cables? To reiterate, I'm listening through Thiel 2.2's and either Satori or Au24 cable (though these impressions were formed only with the Satori, as I'm still evaluating the newer-to-me Audience cables).

Anyway, I'm not sure I can put a tag on which presentation is 'most realistic' so easily. I think it depends a lot on the recording and type of music. As I said above, in general I find tetrode more realistic in terms of qualities I would call 'physical'. But I think triode is more 'accurate' in its tonal and harmonic presentation. I've had some recent success in transforming the tetrode tonal balance more to my liking by both changing input tubes (the previous ones had become microphonic, and were brighter) and by placing tube dampers on them. However, I'm not quite done sorting this all out yet, because I've also gone from Svet 6550C's to EH KT-88's, and on top of that I haven't yet carefully evaluated again the tetrode/triode question with all the new tubes in place. Not to mention that I'm auditioning these speaker cables, which sound perhaps more transiently accurate but less warm than my reference, and I also just had a tweeter and crossover resistor replaced and that speaker is still breaking back in...it never ends :-)

Anyway, yes, my physical impressions are pretty much the opposite of what you describe in your second paragraph above, so apparently our 'clones' are 'slightly off' in different ways. Where you say triode gives you more detail, room ambience, palpability, walk-around transparency, and is more pinned-down in space, I feel tetrode does all those things better, with triode being the mode giving more body/fullness (if less extension and tautness). It's enough to make me wonder if our mode switches are wired-up the same way or if one's reversed! But I guess I envy anybody who's come to the comfortable conclusion that one mode is usually best for them...at some point here I'll revisit this question with the new tubes and post my findings.

I'm using Dunlavy Athenas, a VTL 5.5 pre, ARC CD-2 with harmonic tech pro silways between the CD and the pre and truth links from the pre to the amps (i needed 22 ft so budget had to fit in there somewhere).

I re-read your original post and noted where your switch had to be reinstalled...Putting it in 180 out could be the reason our interpretations are opposite.

As to the conclusion which is best it depends on the music, my mood and whether i have the ambition to get off the couch and monkey with the switch. If i had to live with only one it would be tetrode though...got to have that power when the application calls for it.

I was kidding about the switches being reversed - that's pretty unlikely with two monoblocks, and besides you can't mistake which mode has less power. Last night I did my first listening tests between the two modes with the KT-88's installed. I'm not ready yet to report with certainty, but preliminary results suggest that my impressions will be different with these tubes...

Zaikesman:

I'd be curious to get your report on the KT-88 tubes vs. the 6550s. I called VTL a couple months ago and they advised against any tube-rolling (at least for my amp). So long.

Hgabert: I have been posting my ongoing findings regarding the output tube question on this archived thread, but my comments there do not touch yet on the differences between tetrode and triode with the KT-88's installed. VTL has told me that they've auditioned their amps with KT-88's and liked the results, especially in the bass, but preferred to stick with the 6550C's for the vocal-range reproduction. I don't know what KT-88 versions they've tried to date, but I suspect the EH's were not yet available at the time of the trials Bea described to me, and assume they were Svet's. In my auditioning with the KT-88EH's, I have detected no penalty on vocals compared to the 6550C's, and in fact am now hearing more vocal detail, but as I will shortly go into more specifics about on the other thread, I am reluctant to draw any final conclusions since my 6550C's are over a year old and my KT-88EH's are almost new. Nevertheless, I am tempted to wonder whether VTL's preference for continuing to employ the 6550C might not have something to do with the cost factor - though it's a good enough tube, I am thinking the KT-88EH is better in this application (particularly in the bass), at least in my system and to my ears. I also am currently investigating whether it may possess comparitively greater significant advantages over the 6550C when the two are compared running in triode... :-)