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.
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?