Yep, I leave'em off, if for no other reason than I like to check the bias more often than I want to deal with the covers. But playing with input tubes is a more fun reason.
I'm also just paranoid enough that I prefer an unobstructed view of, and access to, the tubes in case one should give a hint it's beginning to act up; a few times in the past (not always with these amps) I've caught stuff out of the corner of my eye which likely saved me bigger headaches within moments - including smoke wisps emanating from around transformers - that you're not going to notice as easily with covers on. Have you ever done the jump-up and across-the-room-sprint when a tube started in with a light show? :-) And although I think the amps look better with the covers in place, I assume that heat dissipation - and therefore tube life - probably gets slightly improved running naked. |
Update: I just replaced all tubes (input, output, and driver) and I must say that now, triode is a lot better than it used to be. In comparison, tetrode is a little hazy and distant. But triode is crystal clear, and now, for example, the the above mentioned Brahms trio is unbelievable, with fantastic rythm to boot. Also, piano is fantastically present. Take Richter's performance of Beethoven's Appassionata sonata on RCA. You can hear every tap, all the hidden gems, counterpoints, etc. Amazing! And now triode (with new tubes installed) has the power to preserve the waveform, as that piece has incredible dynamics, from ppp to fff.
So, maybe this is what happens over time: as the tubes age and lose power, triode loses its magic, at which point tetrode sounds relatively better. Could it be that simple? |
Don't know if "it's that simple" as you say...I've never found tetrode, whatever its faults, to suffer from being "a little hazy and distant" compared to triode (whether before or after replacing the tubes). I also doubt that amps really lose all that much effective (as opposed to maximum) power in normal use as the tubes age, at least compared to how the sound changes simply from changes in the tubes' response characteristics. I do wonder if all your new tubes are broken in yet, which I find takes several days. But I'm not surprised you've already noticed improved sound overall, and I'm glad you've gotten back in good with triode, which is part of what switching to the KT-88EH's did for me. Keep rechecking the bias over the next week or so, it can take a while to settle in at a more constant level. |
Zaikesman: Thanks, I'll do that. Rechecking the bias is pretty easy to do and doesn't take much time. I guess all I wanted to convey that triode mode (with new tubes) has an incredible immediacy and clarity, which I didn't experience before. |
Are there any real triode amps, or even real triode tubes? When an amp equipped with KT88 or similar pentode tubes is opearated in "triode mode" it means that some extra hardware in the tube (grids) are just left unconnected. Can this be good? |
Eldee: I've wondered about that before myself. In fact, VTL amps always operate with at least one element disconnected, since there is no pentode mode. I think the decision not to run in pentode is probably a good one from a sonic standpoint (I say this not from hifi system pentode experience but with guitar amps), but I don't know how a similar circuit would sound with EL-34's or 6L6's instead. Triode wiring of 6550 types has also been exploited by amp makers like ARC and CAT, so VTL is not alone in considering the unused screen elements to apparently be no handicap. But to answer your first question, of course there are "real triode amps" (and power tubes, which were around before tetrodes and pentodes were invented) - for instance, not even counting all the SET designs, VAC offers high-powered push-pull amps using paralleled 300B's, and the 6AS7 output tube used by Atma-Sphere is a true triode, along with the Russian 6C33C-B used by BAT. |
Zaikesman...EL34 and 6V6 tubes are pentodes, but of course I now remember that the 300B tube is a triode.
I note that a guitar amp is part of a sound creation system, not a sound reproduction system, so sounding "nice"
is more important than sonic fidelity. |
Sorry, my rather obscure point about the guitar amps was supposed to allude to the fact they are pentode (or beam) designs (using EL-34's or 6L6's) which don't sound as natural in fidelity as my (6550-equipped) VTL's run in triode, but do seem to share some of the less harmonius characteristics shown by the VTL's in tetrode. But as you correctly suggest, for a variety of reasons this probably isn't very good evidence for anything though. Anyway, here is an interesting webpage on the main subject... |
Zaikesman...Very interesting indeed. Thanks. |
I had this same swith on a pair of Manley's 120Deluxe Mono amps, and after trying to just stick to one position (including the variable feedback option), I ended up using that unique future depending of the kind of music.
Fernando |
Eldartford: I was prompted to do further research by this question of tetrode vs. pentode catagorization. What I noticed is that beam-tetrodes, lacking the suppressor screen of a true pentode, but with the beam-forming plates (which are not electrically-connected elements of the tube, otherwise known as electrodes) between the cathode, grid, and screen on the emission side and the anode (plate) on the collection side, are nevertheless often described as pentodes or 'beam-pentodes' - even in their original manufacturer's technical description papers. This finding, though I don't know the explanation for it, does help me understand why I've seen certain popular audio output tubes variously refered to as both tetrodes and pentodes in magazine reviews and the like. (Here is a page showing helpful diagrams of the differences.) I also had forgotten that the British "KT" designation in fact stands for Kinkless Tetrode (duh!) - in other words, beam design. So obviously my KT-88EH's do not have an unused electrode element when run in tetrode in my VTLs, and the same would go for 6550's. Further confusing matters (for me) was the fact that my previous tubed audio amplifier used EL-34's (a true pentode) but ran them in ultralinear connection. The RCA 6L6 was apparently the first production beam-tetrode - see this link for the backstory. Though both suppressor screens and beam-formation plates are intended to deal with secondary emission from the anode, it does seem likely to me, as possibly alluded to in the article I linked in my post of 12/7, that the two constructions might behave somewhat differently when triode-connected. |
Update: Tetrode/triode mode appears to be speaker dependent, too. I recently switched to B&W N802s from N803s, and with the Nautilus 802s, I'm back to tetrode for most of the time. Those babies like power, and triode is fine only if the dynamic swings in the musical fabric aren't too pronounced. Tetrode gives a much deeper and wider soundstage, and preserves all of the waveform; which makes for an unflappable presentation.
Well, anyway, I thought I'd post this, I'm just glad VTL provides both modes. With other speakers, it will be different, no doubt. |
Larger woofers to control at the least, and maybe a more difficult impedance, I don't know. The 802 was always my favorite B&W, over the 801, although I haven't really auditioned the N-series. But I never heard one with tubes. Your experience is another bit of evidence suggesting that where tetrode is superior, the extra power may be the main or even the only reason. |
Agreed with Hgabert post entirely, in a way the Triode/pentode switch could be a Hi-End Equalizer for audio setups.
Fernando |
To the extent the switch may act as a bit of a de facto equalizer, that's exactly what I *don't* like about it. As I probably stated somewhere way up above, the fact that an amp can have two subtly different sounds at the flick of a switch just points up the reality that neither presentation can be trusted as accurate. Of course we already knew that, but with amps that don't offer two different-sounding modes, at least the subject isn't put on a platter for us.
I once owned a DAC, briefly, that offered externally-defeatable 'upsampling', in a choice of three different frequencies chosen from moveable jumpers inside the unit. Objective testing by a rather involved methodology I worked out to help me evaluate the effects showed that performance was most faithful to the signal fed the DAC with the upsampling switched off. However, I couldn't deny that there were disks whose sound I subjectively prefered with one or another of the upsampling rates switched-in, even as I could hear some areas of fidelity being compromised. But I wasn't happy that the machine editorialized the sound at all, and luckily my (non-'upsampling') reference DAC outperformed it anyway and I sold the thing.
With the VTL's, I think the ultimate answer would be to get one of the very high-powered Reference models and run it in triode. Answer, that is, if you're a richer man than I...
On a related subject, I spoke with one the technicians at VTL not too long ago and learned that it's perfectly OK to run the amps with tube pairs subtracted, equally from each bank (same number of output tubes removed respectively from both the left and right sides of the chassis, though it's not important that the tubes be from particular corresponding positions within each of the banks, due to the way the amps are wired). This will simply have the effect of reducing power output, with everything else, like the power supply capacity, held constant.
In the case of my 185's, with their three tubes per bank, I can run them at full power (all six tubes, three pairs), 2/3 power (remove one pair), or 1/3 power (remove two pairs, leaving just one pair in the amps). And I have tried this with no problems at all. But for 450 owners, with four tubes per bank, one of the available choices is 1/2 power (two pairs removed, leaving two pairs in) - a close approximation of the same power reduction you get when switching to triode mode. So a 450 owner could compare tetrode mode with only two tube pairs installed, vs. triode mode with all four tube pairs installed, and the prevailing differences would presumably be entirely due to just the different operating modes, without being confounded by different output powers. Just in case any of you 450 owners are feeling curious and experimental... |
Zaikesman: thanks for the above, informative post. I'll try that, as this will be a more "fair" comparison. But in any case, I suspect I will continue needing to run with full banks in tetrode, unless I upgrade to a MB-750, or to the Siegfried (yeah, right!).
I also agree with you that being able to change the sound at the flick of the switch is perhaps "unsettling." But with other amps which don't have a switch like that, the problem just isn't that apparent, but present nonetheless.
Any amp, whether tube or solid state, has a certain sonic signature, let's not kid ourselves. So the VTL amps have two sonic signatures, that's all. |
Exactly right. I got over the 'unsettling'. The 'useful' remains. |
What is the difference between the on/off rocker switch and the on/off rotary switch used on VTL amps? Which is the newer design? Thanks |
If I'm not mistaken, the knob is only used on the double-decker Reference amps, the rocker on the single-deck Signature models and below. I would assume that the rotary switch is heavier duty rated for the higher power; maybe it's a 20 amp part. But I don't know this, and I suppose it could also just be a cosmetic difference. I don't think I recall them always using it on those models, but that observation doesn't prove anything, as they might have recently upgraded the part, just as they've upgraded their fusing in recent years. Call and ask. BTW, VTL has recently upgraded the input stage on the Signature monoblocks to a differential design as in the Ref's, but haven't seemed to advertise the change or its benefits. (Unfortunately, for owners of previous-gen Sig's like me, there is no upgrade retrofit possible.) |
I'm not sure whether or not the upgrade of the input stage to the differential design has any sonic benefits IF one's cabling is all unbalanced, single-ended, with conventional RCA connectors. But it does make a difference if you're running balanced components with XLR connectors (or so I've been told).
Anyway, with my setup, which is unbalanced, it probably doesn't matter. (And in my system, unbalanced actually sounds better, there is more of a texture to the music, whereas balanced conveys a more bland, "bleached-out," sound. I gleaned this from having compared Transparent super unbalanced to Transparent ultra balanced - - but this was, of course, with the old input stage). |
I agree that running XLR into the previous gen VTL amps sounds no better, and maybe just a tad worse than running RCA, even if the preamp is fully-balanced. It has been my experience that between true-balanced components, running XLR usually does sound better - certainly no worse - and I would expect this to hold true for the new VTL's.
It is possible to design a balanced input stage that does benefit from lower noise and distortion even if an unbalanced input is used on the RCA jacks. Converting a single-ended input to balanced before amplifying (not needed for the XLR jacks) can still lower both internally-generated noise, and even to some degree noise picked up by the interconnect, depending on its configuration, although this may not be as effective as if a balanced connection is used. I believe this advantage applies in the case of the new VTL input stage design. It did not apply in the case of the previous gen VTL's XLR jacks, which were included only for the sake of convenience. |
