Another 6550 vs. KT88, 90, et. al.?

Trelja, I read carefully your comments on these tubes in the archived posts. In those threads there were some dissenters who seemed to be expressing basically the opposite view, but many seemed to agree with your take, although this variability could just be an accurate indicator of the importance of any particular circuit in question. This is the most part of why I started a new thread, in hopes of finding a VTL owner or two who've done this dance.

The way we are characterizing the 6550C sound here is reminiscent of the criticisms leveled at the earlier 6550 versions, which I only ever used in Marshall guitar amps. The rep of the "C" is that it is supposed to correct these tendencies. Then again, I've listened to VTL's small stereo EL-34 model in direct comparision to my old EL-34 equipped C-J and not heard any brightness, hardness, coolness, or lack of body in either, though neither possessed the overall fidelity of these mono's.

It is quite possible that the manufacturer's preference for the Svet 6550C is based largely on dependability. I found that I preferred the Svet's to the JJ's when it came to EL-34's (with Sovtek last), both in sound and dependability, but I note you reverse this preference for the KT-88's. I like the sound of EI small-signal tubes but have never heard a power tube of theirs. It would be great if I could find someone in the DC area who's got either KT-88's or 90's and who's curious to do a temporary swap if they've never run the 6550C's as an experiment, but I suppose that'd be a real long-shot.

Zaikesman, if you ever travel up the road to Philadelphi, you are welcome to give my 4 KT90 tubes a spin,
Joe

Trelja, thank you (I do get up to Philly from time to time, my bro lives there), but unfortunately each one of the monoblocks requires 6 power tubes. We could swap 4 of my 6550C's into your Jadis, but of course that wouldn't tell me what the KT-90's would sound like in mine...

Since I've taken the conversation (what there is of it - it seems like maybe I'm not going to find a VTL owner who's done the swaps) away from just a discussion of the various tube merits and into the realm of triode vs. tetrode in the VTL, I want to come clean about something I've glossed over in my response to Mejames. I mentioned that the only two aspects of the sound I thought were superior in triode mode were evenness of tonal balance throughout the range (excepting the frequency extremes where response falls off in comparision to tetrode) and smooth texture (mostly this makes itself apparent on transients such as vocal sibilants).

Things would be simpler if this was really all there was to tell, but that is not true. I left out what is arguably the most important advantage triode has over tetrode, but I did so for a reason. This advantage is in the way triode presents the harmonic structure, which is subtly but distinctly more ear-friendly than the emphasis given by tetrode mode. In this sense, think of flipping the mode switch as somewhat analogous to the idea of changing the nature of the light illuminating the subject of a photograph, its angle and diffusion. The cast lent to the harmonic series of overtones for any sound when in triode mode is perceptably more consonant, tetrode more dissonant. The result is that timbrally, triode sounds more natural.

The reason I chose to omit this distinction above - and it is a separate observation than the simpler question of overall tonal balance - is that I don't expect that this difference between the two modes will fundamentally change even if I install alternate power tube types. Rather, I suspect this phenomenon is inherent to the mode of tube operation. Don't get me wrong - the amp is still plenty listenable in tetrode mode, the slight harmonic hardness (compared to triode) not being obtrusive by itself, and less than other amps I've heard, tube or SS. I do think possibly a different tube type could alter this quality for better or worse - just not change the basic relationship between the two modes relative to one another, but again this is just what I suspect until I do the experiment.

If you haven't already guessed this by now, the total result of my auditions involving the mode switch have yielded paradoxical findings. I can summarize them this way: In all qualities 'physical', tetrode mode is the more convincing of the two. If, when you play a good recording, you try to imagine to what degree the sound reminds you of what it must have been like to be present at the recording session, triode will sound more like you're in an adjacent room to the music-making, listening through a fairly large aperture in the wall, while tetrode by comparision sounds more like you've walked through the door and entered the main room. BUT - and this is the paradox - the tonal and timbral quality of the music you hear in that main room (tetrode) actually sounds a bit more 'electronic' and less 'acoustic' than it did when you were on the other side of the wall (triode). Life is complicated...

Zaikesman and Trelja: I have both a pair of matched quads of EI KT90s, unused (add them to Joe's 4 and you've got your dozen), and a hoard of MO Valve/GEC Gold Lion KT88s, some slightly used. If you're really interested in trying them out to hear the differences (and, like Joe, I think that either of these tube types would be better than the 6550s, but that's personal preference), I'm sure we can work out some arrangement. Let me know, on or offline.

Nice to hear from you RCP. Just like in the majors, 3-way trades are pretty complicated to pull off...Besides, it doesn't sound like either of you guys has any questions about the Svet 6550C's you haven't already answered to your satisfaction? Since Trelja's using his KT-90's, I wouldn't presume disrupt his listening. Russ, if you are saying you're open to something like letting me give a 'workout' to 6 of your spares (for one monoblock - this would actually make for an easy comparision, as I can quickly swap one amp for the other and leave all the tubes in place, and believe it or not I actually prefer to make some critical auditioning tests in one-speaker mono) in exchange for the cost of shipping and a draft pick to be named later, I couldn't refuse. But if you are going to eventually sell these tubes and I don't wind up buying them from you, I wouldn't want to be the cause of you not being able to advertise them as brand new unused. Mail me if I'm in the ballpark...(apologies for corny running metaphor!)