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So my favorite power tube these days is the Genalex KT66 re-issue and I'm wondering how some of the other new production KT66/6L6s sound.
I have the Tung Sol 6L6GC STRs and they have a nice richness to them but I find that the bass is over emphasized (like their 6550 and, to a lesser extent, their KT120).
I'm particularly interested in impressions and thoughts on the following:
Shuguang KT66
Mullard 6L6GC
Tung Sol 6L6G
Sovtek 6L6WXT+
Electro-Harmonix 6L6 EH
TIA
Follow Ups:
The Shuguang Black Treasure KT66 are excellent.
I was worried they might sound a bit lean in the PrimaLuna Dialogue 4, but there is a lovely fullness, without ever sounding bloated. Beautiful detail of timbre. Percussion instruments, including those in the background, have real dimension. Excellent soundstage, side to side and front to back. Bass is very good but not exagerrated.
These follow Genelex KT77, which were extremely good, but the BT KT66 are another step ahead.
nt
I'm surprised that you are using the 6L6 tubes in your Rogue amp. When I called Rogue service, I was told not to the use the 6L6s in my Stereo 100 amp.
Did they say why?
I know I told them I was using the KT66s and I'm pretty sure we discussed 6L6s. The Cronus was originally designed around the EL34 so it could have different parameters than the Stereo 100.
Nick from Rogue said that the voltages used on the ST100 were too high and that he advised me not to use the 6L6. Granted these are two different amps but I thought I would bring it up nonetheless. Dave
Use 6L6GC rated tubes for higher voltages.
TungSol 6L6GC and TungSol 6L6G are good.
Both are GC rated.
DanL
When I said 6L6s, I meant 6L6Gs and 6L6GCs, not the original 6L6s.
6L6GCs are rated to 450V.
Are you higher than that?
KT66s are just 500V.
DanL
I don't know; I should check. I do know that I discussed these tubes with Rogue and they didn't have a problem with them.
Edits: 03/24/15
Hi:
I have used the TS 6L6G in a TAD 60. Great tube. Strong bass, detailed mids, and good treble. From your description of the TS 6L5GC STR I would say these two tube are very simular sounding. Though for me the bass seemed to even out over time. Unfortunately one of them red plated within a year. I went back to my GL KT66s. One other person's account I read on the Tube Store's site is that he had 3 out of 4 tubes go bad. Any way the TS 6L6G bias like EL34s in the TAD 60. 350-370. You may need to check with Rogue about the Chinese KT66s. I think they may have different electical specs than other KT66s. I had NOS Chinese KT66s and the bias was at the very end of the bias range in the TAD 60. I Think the GL KT66 in a great tube, and I doubt you will find a better one from that list. IMVHO. I ran my amp in triode mode.
Good luck.
Michael
Just wondering, have you ever performed any actual frequency response tests when changing tubes? There are many reasons replacements sound different, including the need to retune the amplifier.
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Buy Chinese. Bury freedom.
No. How does one "re-tune" an amplifier?
What TK is talking about is,to really optimize an amplifier when using different tubes,you really should tweak the feedback and the bias for lowest distortion and the best and flattest frequency response..I'm glad he recognizes the importance of audio analyzers and test gear because it really does give you a leg up in performance when you do this.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Ok, got it. I adjust the bias, of course, but I have no way manually to adjust the feedback on this amp and I'm not technically knowledgeable enough to test and change parts.
At some point I'd like to order a custom integrated amp: I'll have to include adjustable feedback as one of it's features.
Thanks!
In addition to feedback and bias, many amplifiers use frequency compensation networks that need to be tweaked when tubes are changed. This all means that the audible effects of tube rolling are really only appropriate for the specific amplifier used to test them. It's not fair to say that this tube or that has better bass, better mids, more air, etc. in a general sense unless each was tested in an optimized environment. Further, it's very possible to overlook the tubes that are actually a best fit if the amplifier isn't retuned for each type. That's the real shame when someone performs tube rolling without test gear. Of course, in the end, tube rolling is about finding the sound you like best. There's still a potential benefit, measurements or not. :)
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Buy Chinese. Bury freedom.
In addition to feedback and bias, many amplifiers use frequency compensation networks that need to be tweaked when tubes are changed. This all means that the audible effects of tube rolling are really only appropriate for the specific amplifier used to test them
BINGO!
You have to admit that the analyzer has showed you a lot of things we took for granted when we rolled tubes..Even hooking a pentode up in triode is going to change because the tube now has a more linear loadline, lower plate resistance, lower gain, and higher transconductance.The problem is,the amp wasn't designed to run this way so when you take measurements in the Pentode designed amp that is wired as a triode,you will see the distortion go up while open and closed loop gain changes significantly.Distortion almost triples in many cases so tube rolling does have its drawbacks even in the smaller tubes because as you say,the values have to be tweaked when you change tubes.
We often hear people say,I put these different number tubes in my amp or preamp and I was floored by results and to their ears that may be the case however,the changes they are hearing may be a rise or dip in frequency response at different parts of the spectrum or maybe a different distortion number..Once they see this behavior on an analyzer,they don't seem to like that tube(s) anymore..Funny how that works..
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Edits: 03/20/15
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