OK, so in an attempt to better educate myself, I thought I'd ask the experts for opinions on this. I did search, but got no real answer....
It has been recomended to put 6CA7's in place of the 6L6GT tubes and re-bias of course in the Ming-Da MC34-B amp.
Ok, I can accept that, but WHY? What is the reasoning behind this, besides more output power? I'm trying to better understand this.
As it is, the amp sounds pretty good to me. So I have been reading reviews etc. on tubes. This tube is more defined, bass is tighter, bla bla.... Man, this is confusing stuff. If there is this ultimate output tube, then why are there so many others??
"It just sounds better" is not enough for me. I need some electonics theory to back this up. Anyone want to take some of the Voodoo out of this for me?
My brain hurts....
Marc
It has been recomended to put 6CA7's in place of the 6L6GT tubes and re-bias of course in the Ming-Da MC34-B amp.
Ok, I can accept that, but WHY? What is the reasoning behind this, besides more output power? I'm trying to better understand this.
As it is, the amp sounds pretty good to me. So I have been reading reviews etc. on tubes. This tube is more defined, bass is tighter, bla bla.... Man, this is confusing stuff. If there is this ultimate output tube, then why are there so many others??
"It just sounds better" is not enough for me. I need some electonics theory to back this up. Anyone want to take some of the Voodoo out of this for me?
My brain hurts....
Marc
I am no expert, but...
Well, say you change the output tubes for the EL34's ... there are still plenty of different brands of 6CA7/EL34 around, which will, you will read, all give subtle differences in sound. And so it goes on and on and on.
The short answer for
Sit back, listen to the music and relax - and do not read to much threads: you will dispair among the different tubes used through the people around here. But if you insist, I can recommend Morgan Jones Valve amplifiers, thirf edition: reading in it you will understand the amplification step by step... and then, you will get more dispaired, as you will soon note that it is not just the output tubes that influence sound, but also the driver tubes, trafo's, power supplies, wiring, capacitors...
you have been warned 
Have a nice weekend!
Erik
Well, say you change the output tubes for the EL34's ... there are still plenty of different brands of 6CA7/EL34 around, which will, you will read, all give subtle differences in sound. And so it goes on and on and on.
The short answer for
is: there is no ultimate tube. Just like there is no ultimate sport car, no ultimate blabla... I once read, here at diyaudio, a comment by someone: 'the fact that there are so many CD players around indicate there is no ultimate - there are lots of different tastes' (or something like that). Engineering is about compromises...
Sit back, listen to the music and relax - and do not read to much threads: you will dispair among the different tubes used through the people around here. But if you insist, I can recommend Morgan Jones Valve amplifiers, thirf edition: reading in it you will understand the amplification step by step... and then, you will get more dispaired, as you will soon note that it is not just the output tubes that influence sound, but also the driver tubes, trafo's, power supplies, wiring, capacitors...
you have been warned Have a nice weekend!
Erik
Runco990 said:
There are a lot of answers that you might get. Take a look at the data sheets for the two tubes, pay close attention to any differences, then pick any that you like.
Obviously, I'm not being very serious. The problem is, any theoretical explanation as to why one tube sounds better than another (to any particular person) is useless unless it is predictive. It's not enough to be merely descriptive.
In other words, suppose you pick the fact that 6CA7's have higher transconductance (sensitivity) than 6L6's as the reason they sound better in an amp. In order for it to be a useful theory you would need to show that you can pick another tube with even higher transconductance, and that that tube will necessarily sound even better. If you can't do that, then the theory is not really a theory at all, it's just a guess. Some might call it a hypothesis, I call it a guess.
Unfortunately, I expect that all you're going to get are guesses. Maybe I'm wrong. Don't misunderstand me, I think it would be great if I'm wrong, but I don't think I am. After spending decades experimenting with these things I've come to accept that there is a certain amount of black art involved. I don't believe in magic, but black art ...
-- Dave
I have used both EL34 Svet, 6L6GC Svet and Sylvania NOS 6L6GB in my amp. Now I experiment with KT88 EH.
My experience is that the higher gm tubes give more output, are easier on the phase splitter and create more open loop gain so that the global feedback rises more and lowers Zout, noise and THD. Now there are tubes and tubes. For instance I have listened in a guitar amp RCA black plate NOS 6L6GCs killing Groove Tubes EL34. In general when your transformer reflects 6K to the primary the EL34 is going to give 40% more wattage than an 6L6GC with less Zout. EL34 sounds more rounded and 6L6GC flatter. It depends very much how your driver stage, B+, mains trans VA and global feedback are optimized. If you have say 450V B+ and 0.6A stereo (4Xtubes) capability you can push 6L6GC to 55ma and make it sound dynamic yet not rounded. For 40-45mA I would bet on a good EL34 over a good 6L6GC. But one tube that may please you very much, that retains the gain and output in an EL34 amp but sounds bigger and less distorted is KT90. Sadly EI Serbia stopped it and its NOS now, but the new KT90EH is almost as good but far more reliable than post raid produced EIs.
My experience is that the higher gm tubes give more output, are easier on the phase splitter and create more open loop gain so that the global feedback rises more and lowers Zout, noise and THD. Now there are tubes and tubes. For instance I have listened in a guitar amp RCA black plate NOS 6L6GCs killing Groove Tubes EL34. In general when your transformer reflects 6K to the primary the EL34 is going to give 40% more wattage than an 6L6GC with less Zout. EL34 sounds more rounded and 6L6GC flatter. It depends very much how your driver stage, B+, mains trans VA and global feedback are optimized. If you have say 450V B+ and 0.6A stereo (4Xtubes) capability you can push 6L6GC to 55ma and make it sound dynamic yet not rounded. For 40-45mA I would bet on a good EL34 over a good 6L6GC. But one tube that may please you very much, that retains the gain and output in an EL34 amp but sounds bigger and less distorted is KT90. Sadly EI Serbia stopped it and its NOS now, but the new KT90EH is almost as good but far more reliable than post raid produced EIs.
Here's someone who did what you are suggesting:
http://audiokarma.org/forums/archive/index.php/t-35775.html
Jeff
http://audiokarma.org/forums/archive/index.php/t-35775.html
Jeff
Sal Brisindi said:
After much reading, apparently it can. My guess is they just used the same transformer from the MC34-A, which takes EL34's as well.
While they MAY use different OPT's, I doubt they'd make a different main transformer for a product so similar.
Guess I'll find out. I decided to pick up a set of winged =C= tubes and listen for myself. I would have replaced the chinese tubes anyway, so why not. I'll also pick up a set of =C= 6L6GC's just to do some listening tests. I guess it really boils down to that.
Marc
Hi Marc,
Sal got to the heater current issue before I did. Worth mentioning for sure.
Now, 6L6GC has a max. plate dissipation of 30W, EL34 and 6CA7 are around 25W. I think the design of the circuit determines the best output tube for it. I would tend to stick with 6L6's and try the 6L6EH. If you go for EL34 types, I have found a 6CA7 tends to sound better. At this time I'm using 6CA7EH's and I'm very happy.
-Chris
Sal got to the heater current issue before I did. Worth mentioning for sure.
Now, 6L6GC has a max. plate dissipation of 30W, EL34 and 6CA7 are around 25W. I think the design of the circuit determines the best output tube for it. I would tend to stick with 6L6's and try the 6L6EH. If you go for EL34 types, I have found a 6CA7 tends to sound better. At this time I'm using 6CA7EH's and I'm very happy.
-Chris
The reason why some people like pentodes while other people like beam tetrodes is largely a matter of personal taste and sometimes prejudice or peer pressure.
The reason for the existence of both types of power tube in the first place came about when the beam tetrode was developed to get around a patent that had already been taken out by rival manufacturers on the pentode. Beam plates were found to be a practical alternative to the suppressor grid for overcoming the tetrode 'kink'.
Once the beam tetrode was established, its manufacturers naturally carried on producing it and endeavoured to gain and maintain a good share of the power tube market. The pentode manufacturers did likewise. Hi-Fi amp builders seemed not to be particularly devoted to one tube type or the other, but guitar amp builders were somewhat polarized, e.g. Mashall liked pentodes (EL34) and Fender liked beam tetrodes (6L6).
Pentodes and beam tetrodes do much the same job but are not always plug-compatible, because they have different needs. In general, pentodes can tolerate higher screen voltages and higher values for grid leak resistors than beam tetrodes. This can make pentodes a bit easier to drive. If beam tetrodes are subsituted in amp designed for pentodes, without making any circuit changes, it could cause poor performance or tube damage.
The reason for the existence of both types of power tube in the first place came about when the beam tetrode was developed to get around a patent that had already been taken out by rival manufacturers on the pentode. Beam plates were found to be a practical alternative to the suppressor grid for overcoming the tetrode 'kink'.
Once the beam tetrode was established, its manufacturers naturally carried on producing it and endeavoured to gain and maintain a good share of the power tube market. The pentode manufacturers did likewise. Hi-Fi amp builders seemed not to be particularly devoted to one tube type or the other, but guitar amp builders were somewhat polarized, e.g. Mashall liked pentodes (EL34) and Fender liked beam tetrodes (6L6).
Pentodes and beam tetrodes do much the same job but are not always plug-compatible, because they have different needs. In general, pentodes can tolerate higher screen voltages and higher values for grid leak resistors than beam tetrodes. This can make pentodes a bit easier to drive. If beam tetrodes are subsituted in amp designed for pentodes, without making any circuit changes, it could cause poor performance or tube damage.
Runco990 said:
Marc, you're in the wrong hobby then! Tubes will never measure up to solid state. I think you need to take a leap of faith here and realize that for all of our technology - we can't measure the numbers that actually represent what makes one amp sound better than another.
Tubes are constructed differently and with different materials and thus sound different, just like a paper woofer sounds different from kevlar one.
As for 6L6 vs. EL34 -- it is a matter of personal taste. I prefer the EL34 in my guitar and audio amps myself, but others like the 6L6. However, if I had to choose between chinese EL34s and NOS GE 6L6s.... I'd take the 6L6s because they would be a much better tube! Again, tube construction matters! As for choice, there seems to be a good selection of both tubes in production. You can try both in your amp and see which you actually do prefer! That's part of the fun! Let the tube rolling commence!
Probably the best advice I can give you is have patience. Tube amp building and learning is something you really acquire over years... not days. The good thing is, even poor quality tube gear still usually sounds really swell.
Also, one addition as was noted above --- the 6CA7 and the EL34 are electrically equivalent tubes, but not constructed the same. Obviously the plates are completely different -- inside the EL34 is a true pentode and the 6CA7 is a beam tetrode. So while they are plug and play exchangeable... they will sound different!
Runco990 said:
Fact is: you're not gonna get any "real answers" simply because psychoacoustics includes a considerable amount of variables, and no one really knows what to measure. Look at the specs: 807 Class AB1 has a THD figure of 1.8%, and the 6V6 comes in at 3.5%. So 807s must sound better, right? So how is it that the raves for the sonics of the 6V6 are universal? Some folks have doubts as to how 12AU7s sound, but I haven't seen anyone say that 6V6s sound bad.
I did a project using 807s, and found that the THD spec was spot on. However, running completely open loop, with no feedback of any sort, the 807s had an edgy nastiness in the upper mids and highs that was very annoying and would quickly wear you out. I included both local NFB (indeed, the inventor of the type (O. Schade) recommended lNFB) and gNFB to tame that, and make for a really good-sounding amp.
The latest project was based on the 6BQ6GTB horizontal deflection power final. The loadline for that came in with an h(3) estimate of 5.0% (although it measured more like 3.0%) but still higher than the 807 amp when running open loop. You'd think that the 6BQ6s'd sound worse. However, that wasn't the case, as there was hardly any outright pentode nastiness unless the volume was set too high anyway. For this design, based on what I heard while playing it open loop, I decided to not install any local NFB, and rely on gNFB only to take the edge off the highs, and for improved woofer damping. How does something like this happen? How is it that the "superior" audio VT needs more help from NFB than a type that wasn't intended as an audio final, and whose spec sheet includes no data for audio useage. Indeed, the 6BQ6 sounds like a 6V6 on steroids from what I can tell. Good thing no one has discovered this since 6BQ6GTBs are widely available, and at a price way lower than any "audio" VT, and it can certainly hold its own with the 6L6s/6V6s/EL84s/EL34s/KT66s/KT88s/ad infinitum.
Then you have the whole true pentode/beam tetrode/pseudotriode/triode controversy. The wrangles over topologies (PP vs. SE; Ultralinear vs. parallel lNFB vs. no NFB) Classes, and who knows what else. And that's before you even get to the small signal VTs. I figure that the best thing to do is say "T'hellwiddit" and put that "evil" gNFB to good use for what it was intended to do: make the end performance less dependent on the open loop performance and components.
Sandy amp designers have it a good deal easiler, since there aren't these fusses over transistor or IC types ( and there's a reason for that as well).
Hi Miles,
LOL!
Have you looked at the Bob Cordel threads? There is a high amount of voodoo and snake oil in every audio pursuit. There is even talk of how good the old Germanium transistors sounded in the SS forum.
Then there are the classes and output stage configurations, input stage configurations. It never ends. So, it's about the same as here.
-Chris
Ahhhh, I disagree.
LOL!
Have you looked at the Bob Cordel threads? There is a high amount of voodoo and snake oil in every audio pursuit. There is even talk of how good the old Germanium transistors sounded in the SS forum.
Then there are the classes and output stage configurations, input stage configurations. It never ends. So, it's about the same as here.
-Chris
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