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My question up front:
- What are the technical differences between a EL34/6CA7 tube vs the KT77?
- What are the sonic characteristics of a KT77 vs the EL34/6CA7?
I've been playing with different power tubes lately in my Rogue Cronus Magnum integrated and I'm curious about the KT77 types.
First, I assume [correctly or incorrectly] that the 6CA7 will sound similar to EL34's? I was told long ago that the 6CA7 is like a more rugged EL34. So I've had a couple different brands of current production 6CA7 in my amp and they sound nice enough to me. I do prefer them over the larger KT120's.
In my email exchange with "Nick" at Rogue about bias settings he mentioned the KT77 as being a nice sounding tube to try but he didn't go into any details.
Thanks!
Follow Ups:
The beam tetrode KT77 has a sound that is more in line with what you're already hearing in the KT120's. I was never a fan of that tube. In short the KT will not bring out the midrange that a EL34 can offer. The newer EL34's have also managed to bring more extension to the table.Also look into the TungSol EL34b as recommended to me by Jim M. A very rugged tube. It also has some of the best extension both top and bottom I've heard in an EL34 while still maintaining that midrange magic.
Edits: 03/14/23 03/14/23 03/14/23
Thanks! With all the EL34 variants I could go broke trying them all. I'll keep the TungSol EL34B in mind and I believe JoshT likes the JJ EL34II in his Cronus Magnum.
For my CM I have:
- JJ 6CA7
- EH 6CA7
- KT120
this link has some great information about the differences in the old production 6ca7 beam power tubes vs. the el34 pentode tubes.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/13/23 03/13/23
Thanks for that Wikipedia link. Did you see all those PDF downloads in the References section at the bottom? Many of them are complete scanned book PDF's on vacuum tubes. No, I haven't read them! I just skimmed a couple.
Hi Abe,I've now spent over a week comparing my JJ EL34IIs to my JJ 6CA7s in both my Rogue Cronus Magnum II and my ST-70 modern build amp.
My conclusion is that the JJ versions of these two tubes sound very similar, but the EL34II wins in the ST-70 / Devore Super Nines system and the 6CA7 wins in the CMII / Klipsch Heresy II system. I find that the EL34II is a bit more expressive - it is more detailed and forward from the midrange up to the treble, and has tighter, "pluckier" bass. On the other hand, the 6CA7 strikes me as a bit more linear from top to bottom, with deeper bass and an overall rounder, more laid back sound. Also, the 6CA7 *looks* better in the CMII because it's closer to the width of a 6550 so it doesn't completely vanish in the recessed sockets like the EL34II does. Since the ST-70 doesn't have recessed sockets, the svelte EL34 profile looks less tiny and more elegant. If that matters, lol.
You might want to check out the link below from the JJ site. It's pretty fun in that they describe the technical aspects as well as the sound profiles of their various EL34 types narratively.
I've put their descriptions together below so you need not click on each tube type to see them:
"EL34 is an octal power tube with a maximum plate power of 25W. Very robust and reliable due to its internal construction."
"E34L is a more powerful EL34 with more headroom and deeper lows. It is a little more aggressive than the EL34"
"EL34 II [which I have] has fuller low mids and low end but does not lose headroom in the high end. Stronger than regular EL34 but not as aggressive as the E34L."
"6CA7 [which I also have] is a beam power pentode with octal base. It can be used in most EL34 amplifiers. Even more powerful than KT77, and very similar to 6L6 sound. The 6CA7 provides a typical American sound."
and
"KT77 is a beam power pentode with octal base. It can be used in most EL34 amplifiers. It has more power, fatter bass and more headroom than the EL34 and E34L while providing very detailed tones."
I was surprised to see that they describe the 6C7A as more powerful than the KT77. YMMV, naturally, as may similar tube types from other manufactures, but I found the descriptions pretty interesting, though I suspect they might be more oriented towards guitar amp users?
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."
Edits: 03/13/23
Anyway, thanks for the nice comparison.
Open up your mind, in pours the trash. - Meat Puppets, 1987
"beam power pentode" and "beam tetrode" are interchangeable language.
Also "beam power tube". All three have been used over the years to describe a tetrode with beam forming plates between the screen grid and the plate of the tube.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
But doesn't the pentode have an additional beam forming plate, so the the two aren't exactly the same; tetrode with four elements (cathode, control grid, screen grid and anode) and pentode with five elements, the fifth being the suppressor grid? If there are only four elements in a KT77, why would you want to call it a pentode? Do you believe the two function in exactly the same manner?
Open up your mind, in pours the trash. - Meat Puppets, 1987
No, a true pentode (el34) has a cathode, control grid, screen grid, suppressor grid and a plate. No beam forming plate at all. Just a cathode a plate and three grids in between.some people call a beam power tube a pentode because they consider the beam forming plate to be a fifth element.
A beam power tube does not function exactly like a power pentode but close enough that it can be a direct drop in replacement. 6ca7 for a el34 for instance.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/15/23
Yes, you are correct in that regard.
Open up your mind, in pours the trash. - Meat Puppets, 1987
Must be a typo on the JJ website because I cut and pasted in their language, but I should have flagged that. Interesting.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."
Thanks for summarizing the sound of the various JJ tubes, and for the link to their website. I have the JJ 6CA7 back in my CM and I'm liking them more now than what I heard initially. They seem to have a richer sound overall than my EH 6CA7. I tried the KT120 again too. None of these are bad sounding tubes but the KT120s seem tighter (faster?), a little less robust or rich, but powerful and snappy.
If the KT77 offers fatter bass, I might have to try those out. I enjoy a fatter more robust sound when it comes to tube amps.
Have you set your CM to 4 ohms or 8 ohms? I know the former sounds tighter than the latter, which is why I ask.
I switched mine from the 8 ohm setting to the 4 ohm setting a few years ago to run mine with a pair of vintage Ohm Model L speakers, which are 4 ohm nominal, and it was a noticeable improvement (the Model L has great deep bass for its size but can be a bit loose, and the switch tightened it up without thinning it out).
I figured I'd want to switch back to the 8 ohm setting when I paired it with the Heresy IIs since they're a bit bass light, but actually they've never sounded fuller or deeper so I'm not touching the setting. And that's a good thing because it's a PITA to do so with that amp. ;-)
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."
I tried the 8-Ohm and 4-Ohm taps when I initially setup the amp over a decade ago. I decided that my CM sounds better overall on the 4-Ohm taps with my 6-Ohm nominal Tannoys.
One channel was easy to do but the other side was very confined and difficult to reach. I believe Rogue added a Triode/Ultralinear switch in newer models but still no 8-Ohm/4-Ohm toggle.
I am following along with all this tube info. Good stuff! My CM2 is not going anywhere.
Mine was set to 4 ohms because my Usher speakers were 4 ohm. Just changed it back to 8 when I got my Fritz Carrera Be's, 8 ohm min 6 ohms. They have a benign impedance so back to 8. Yes it's terrible changing the CM2 over. Mark needs to put in some kind of switch!
Abe,Josh keep your observations coming.
Edits: 03/16/23
but I can put in a good word for the JJ KT77. A nice sounding tube in my Rogue Stereo 90, although I would not call them "rich" sounding. More a linear sounding tube with nice detail, but with a little more midrange bloom than the Tung Sol KT120s.
KT66 the best sounding tube in that amp in my opinion.
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