EL34 vs. KT66 output tubes

I've had the recent opportunity to compare EL34 and KT66 output tubes in my AES sixpac monobloc amps (the amps come with the EL34's). I am surprised how much more I like the KT66's. Male vocals in particular seem to really reach out much more with the KT66's. Although bass might not be as deep as the EL34's, it has a warmer rounder feel. Is the KT66 known to be a warmer sounding tube? Does anyone have experience with both of these tubes?
WHICH '34? WHICH '66? I suspect there are more variations among brands WITHIN the tube type as between the 2 types.

"Male vocals in particular seem to really reach out much more..." means male vocals are more forward?

I would be interested in which KT66 tubes you rolled. I have the Six Pac's and have not yet rolled any of the power tubes.

The EL34's are the Ruby EL34B STR. I'm not sure who makes the KT66's; the writing on them is "Electron Tube KT66 Made in China". I thing the brand might be Shuguang. I got the first set of KT66's from Cary, and the 2nd from Upscale.

What I mean about the male vocals reaching out, is that they just seem to have more presence, like they are closer to me and a little more gutsy. Maybe the KT66's have a bump in the lower midrange? Anyhow I really like the effect. It actually sounds more realistic to me, like I am more in a concert hall. I had to go back to the EL34's for a while until I got a new set of KT66's, and I thought there was definitely a bit of lost 'magic'. I would love to try a more 'exotic' KT66 like the Genelax, but holy cow, are these expensive!!

Matty, if you decide to try the KT66's, I would be very curious to hear your comments. Be aware though, that you lose a bit of power; I think the KT66's provides around 35wpc as opposed to the 50wpc from the EL34's. No problem for me as I am using fairly efficient speakers, and it goes as loud as I need.
By the way, it was the folks at Cary that suggested the KT66. I called them asking for suggestions based on my comments and the type of music I mostly listen to, and they thought the KT66 would work well... they were correct!
Well, that's why they make vanilla AND chocolate.

Most people, me among them, prefer the EL34 over the KT66 (and 6L6/5881), but the important thing is that you have found YOUR best tube!
For Push and Pull tube amps,
I always prefer 7027, KT66, 7591 and EL84 over EL34.
The vocal always sound richer over all than EL34.
The bass on EL34 is not neccessary better. It really depends on which brand/type of the tube and the amp you installed them on.
Always prefer the NOS tubes over the modern Chinese and Russians.
Yes, 'richer' is the correct word for what I am hearing. I little more forward as well. I like the bass with the KT66's; it seems a little rounder and fuller than with the EL34's, although maybe not quite as deep.
"Most people, me among them, prefer the EL34 over the KT66 (and 6L6/5881)"
Trelja, I wouldn't say most.
9 out 10 audiophiles I know around NYC prefer the KT66 ( none chinese nor Russian ) over the EL34 ( all types )
Amp has a lot more to do with the tube.
Maybe most of the EL34 amps I've heard are less musical to our ears than the KT66/7027/6L6GC type of amps.
The only exception to our ears is the Vintage Marantz 9 PP amp from the 60s. That's the only EL34 amps we really like. Powerful yet musical ( except for the price tag.)
However, we did easily find many other KT66/7027/6L6GC and EL84 amps ( use it on higher efficiency speakers ) that sounded much better than the rest of the EL34 amps.

One should focus on the amp design and not the tube choice.
Trelja, I'm curious as to why you and others prefer the EL34 over the KT66. What are the characteristics of the EL34 that you prefer.

Chang, you mentioned a couple of times about not using the Chinese or Russian KT66's. Which brands to you recommend? Are there really good KT66's around that are not astronomically priced (I need 12 tubes)? What are the sound quality differences over the Chinese or Russian versions?
For Push and Pull application,
I got great results replacing KT66s with NOS 7027A for my application.
The 6L6GCs lacks control in lower frequency when compared to 7027A. Some might like the rounder and fuzzier sound of the famous black plate 6L6GCs.
The Russian and Chinese KT66s sounded even worst than the NOS 6L6GCs. A bit harsh which cause long term listening fatigue.
I don't really hear much difference between the RCA/GE/Sylvania tall/short bottle 7027As. Some of my buddies thought the RCA/GE sounded slightly warmer then Sylvania but we can't tell the difference during blind test.
Been trying to post to this thread for several days with no luck. Not sure why...

S23chang, while I do not doubt your assertion, the number of EL34 tubes/amplifiers sold compared to the 6L6 variants shows that people do prefer the EL34 tubes as we are voting with our wallets. One of my amps can run 6L6, EL34, KT88, KT90, 6550, and while I personally run KT88, I have also used EL34s, but will not be buying any 6L6/KT66/5881 in the future.

Smeyers, for me, the midrange purity of the EL34 does it. In some amps I have heard, experiencing what feels like the perfect reproduction of much of the music is a tremendously endearing (and fleeting) quality. Neither tube is as good in the treble as you can find, though I will still opt for the EL34 in the high frequencies. And, also neither tube is particularly special in the lows, I will give credit to the 6L6 variants being superior there.
FYI, I should clarify that I'm using only vintage gears because I prefer the sound from vintage gears much more than the modern gear.
I do agree that the modern EL34 amps sold a lot more than the modern 6L6 variants because no manufacture makes any good modern 6L6 amp these days but it does not imply that 7027/KT66/6L6GC are not as competent.

Also, not all 6L6 tubes are equal. 7027/KT66/6L6GCs are the high output tubes in the 6L6 family. They can produce same amount of power as the EL34 type.

The 6L6 variants were used for many guitar and organ amps.
There are abundant supplies of NOS 6L6 tubes. I'm not sure why manufactures today didn't pursue making the KT66 amps these days. Profit margin or it is hard to design a good KT66 amp these days since there werern't many clone circuits and good transformer available?

As far as EL34 vs KT66 tube goes for the modern home audio equipment, the modern EL34 has much higher demand and longer history than the modern KT66 due to hard to find NOS EL34 mullards and Telefunkens. Therefore, the Eastern European EL34 tubes has come a long way to make something decent when compared to its KT66 line.

I would not buy any modern KT66 amps in the future either.
I would buy the vintage PP KT66 amps.

Our friends here in NY definitely prefer the KT66/7027/6L6GC and EL84 over EL34 because the mids sounded more full bodied. Not sure if that was the reason why they use these tubes for guitar amps. They seemed to match our speakers much better than EL34s.
The EL34 might be more balanced for rock music but not the string instrument, vocal, saxaphone and drums just don't have the authority and tonal quality we like ( again, except for Marantz 9 mono blocks from the 60s.)

Again, just my opinion. I couldn't stress enough about amp design.
S23chang, I don't think we disagree.

Having laid out your case well, along with things that most people often neglect to include in the mix such as type of amplifier and speaker as well as musical preference, it's easy to see where you are coming from. I don't doubt the 6L6 variants are best for you and your associates.

On my own end, I should submit to you that I am using amplifiers from the past decade, with speakers of the same vintage, and tend more to rock, jazz, and popular music. And, to be honest, when all is said and done, so far, I have hitched my wagon to the KT88, though we'll see with a new amp coming whether or not I will revert back to the JJ E34L.

While our means and ends seem to be different, we both are looking for the best possible way to enjoy the music we listen to. In the end I guess I have to repeat my assertion, that's why they make vanilla AND chocolate.
Trela and S23chang.As you both well now, there are terrific examples of each of these tube topologies. Saying one tube is better than the other is like saying "a ferrari is better than a benz". Like Trela says "Some preferr vanilla to chocolate". S23chang alluded to his preference to vintage amplifiers over the more modern designs and I can understand his anology here as many of the better vintage amplifiers of the day employed top shelf output transformers when compared to the standards of today. However....chang also mentioned the marantz model 9. An obsenely expensive amplifier in it's day, the sota amp of the era that would still be competetive with the top shelf stuff being offered today.That said: The marantz 9's were never really sold with el-34's as the output tube per sey, The tube employed in them was actually the genelex kt-77, a beam power tube that would electrically sub for the el-34 [a pentode]. And once the comsumer got a taste of the Kt-77, many of Marantz's customers would also purchase the kt-77 as a more expensive option for the Marantz model 8b as well. The kt-77 is a beam power tube similiar to the kt-88 and possesses a kt-88esque like bass quality combined with the more liquid mids of a good nos el-34 and the air,purity and finese in the treble region of a nos el-84. It mainly comes down to output power and the amplifiers ability to drive a given load. Ever heard the Conrad Johnson premier 8XS with el-34's in it? Obviously not your typical el-34 based amplifier and sounds nothing like your typical el-34 fitted amplifier based on that tube topology regardless of vintage or modern. Some of the more recent amplifiers designed around the el-34 are very very good indeed in that they capture the frequency extremes as well as the endearing qualities of the midrange in a way the older designs failed at.Have a listen to the German made Klimo Kent,a 35 watt el34 based amplifier that been around now for 10 years or more. World class by anyones standards to be sure! or the decade old el34 based amplifier by Beard in England to name a few. The kt-88/6550/6L6 family of amplifiers introduced in that era were really brought to the market primarily because of their higher power offerings. Speaker design was making a radical shift away from the large high efficient speakers to smaller design's that required more power. Given the proper speaker load on the amplifier.... all things being equal here....and personally speaking here.... In most any given push/pull circuit, I would choose the qualities of the el-84/6bq5 family of pentodes over any of the el-34,kt-88,6L6 family of tubes because,like the kt-77.... it possesses and combines the best qualities of each of those tubes. I have heard some mediocre,some good and some great sounding amplifiers with each one of the above mentioned output tubes. All things being equal.... and like s23chang,dollar for dollar I would lean toward the fine vintage amplifiers of yesteryear. That said: Many of the great [read expensive here] modern tube amp designs of the last decade are becoming available on the used market at prices below the very best of the vintage years.