VTL Tetrode/Triode

Hi Hgabert

In my experience (Manley 200/100 Mono's, very similar circuit to your MB's)), in absolute terms, the amps always sound better in triode: much more refined sound, better detail, less grundge, etc., etc. Tetrode becomes advantageous when your system, wether because of your speakers' efficiency, or your preamp's gain characteristics, benefits from the extra power. If your speakers are efficient enough to meet all of the needs of every type of music that you listen to, at every loudness level that you listen at, with the amount of power that triode has to offer, triode may always sound better to you. It sounds like they are not; few are.

I found that in my system, with many speakers, tetrode not only allowed the speakers to play louder, with more bass, but more importantly, it let the speakers unravel complex orchestral passages, it let a string section sound like many individual players as opposed to one large mass of "string" sound; probably why the Vivaldi sounds better in tetrode. Most reggae, while "bassy", is not particularly complex music; so will probably tax the amps less. The problem became that I missed the purity and sweetness in the highs that triode offered. The solution for me was two-fold: get used to listening at slightly reduced volume; this taxed the amps (and my hearing) less, in triode mode, and experiment with the input tubes. I found that with the right NOS 12at's (for me it was W.German Amperex or Tele's), there was enough of an improvement in the detail and treble extension departments, in tetrode, to bring the sound close, if not quite, to the level of triode sound with run-of-the-mill 12at's. This allowed me to enjoy tetrode mode when I absolutely had to have the extra watts. Of course, the sound in triode became that much better also; and this is why it is called "audiophilia nervosa" :)

Good luck.

The 6350's affect the overall sound less than the 12at7's do. It still pays to experiment, though. This is an American made tube and there are no exotic versions available, to the best of my knowledge. My favorites are the Tungsol's and the earlier RCA's. The RCA's that I have (two different vintages/two different internal construction), sound a bit more relaxed and romantic. The Tungsol's sound a bit more dynamic and alive, with a more prominent top end; this better suited my system. The differences are relatively subtle; but a definite improvement over the GE's that came in the amps. Try "Antique Electronic Supply" as a source of 6350's.

As far as 6550's go, I really don't have an opinion since my amps use 6L6GC's. I will say that the Sovtec 6L6's that the amps came with sound less refined than the NOS GE's that I have. The GE's are not a particularly great tube either, but in my system, a better sound. I hear good things about the Svetlana's; maybe worth a try. By the way as far as the 12at7's go, the Telefunken CCa (a super-premium version of the 12at7) is supposed to be THE tube for these amps. Very expensive, though.

Have you experimented with power cords? My amps definitely benefit from upgraded power cords. I use the old Tiffany "reds". Recommended by the Manley's themselves as the chords for these amps. This is going back several years, however, and I'm sure there are better cords out there for these amps, by now. The improvement over the stock chords was unmistakeable, however. Gutsier sound, with larger soundstage and more refinement. My amps also like to be placed on hard cone-type footers. The soft type makes the same a bit ill-defined and tubby. And finally, VPI bricks on the transformers are a very worthwhile tweak; the tighten up the sound, and make the spaces between instruments cleaner.

Good luck.

Try listening at reduced volume, and I think you will find that triode has a decided advantage over tetrode, even with large-scale, complex orchestrations; the issue is simply that to unravel and amplify a complex signal, more power is needed. It's not that tetrode ever has an advantage, per se, it's that when the music is more demanding, the extra power makes up for any loss in transparency that triode provides under ideal circumstances (higher speaker efficiency). Conversely, try turning the volume up, higher than normal, while playing small cale jazz or classical. I think you will find that you lose the detail and purity.

I think that we can all agree that filet mignon is a better cut of beef than sirloin; but if the budget only allows for one pound of filet, and we are trying to feed six adults, would it not be more satisfying to buy two pounds of sirloin, than one pound of fillet. Poor analogy, perhaps, but the point is that I think that if you were to compare tetrode to triode, using something along the lines of a Klipsh corner horn with it's extraordinarily high efficiency, it's unlikely that there would be any advantage to tetrode mode; unless, perhaps, if you were trying to fill some incredibly large space with sound.

By the way, it is not necessary to turn the amps off to switch between the two modes. You simply have to be sure there is no signal running through them: mute the preamp.

Yes, it is true that you don't HAVE to turn the amps off; according to Manley. However, by turning them off, I suppose the problem of forgetting to mute the pre becomes irrelevant. NO SIGNAL THROUGH THE AMPS WHILE SWITCHING!

Again, I found that if the goal is the purity and detail of triode mode, that any kind of compliant isolator sent the sound in the opposite direction. For me, hard cones between the amps and sandstone slabs(on the floor) gave the tightest and cleanest sound. Sorbothane tended to blur images and make the amps even more "tubey" sounding.

I'll stick to my comments about triode/tetrode. IMO, given the same circuit, triode operation is always superior. Does one then have enough power for the speakers being used, however?

Lastly, make sure that your tubes are biased properly! This will definitely affect the sound.

Happy listening.