I got my Zana #12 the day before Headfest and have done a good bit of rolling of the 6sl7. I included the AT ad2000's in the title because I think there is a great synergy with these cans and the ZD. I started with 8 tubes but half of them were lesser versions of the final 4 that I picked up for cheap hoping to find a bargain tube to recommend ( when talking about a $2k amp saving a couple of $10 didn't make much sense though). These tests were with the Tung-sol 6dt4 rectifiers Craig supplied with the amp. The amp has well over 200 hours on it and the source is my modded Technics rs1500 reel to reel tape with orchestral and acoustic jazz recordings.
the finalists were; Sylvania Jan-CHS-6sl7GT/VT229 1950's, Tung-sol CTL SU7GTY 1950's, National JAN-CNU-6sl7GT/VT229 1940's, and RCA 5691 red base 1940's.
Sylvania-seemed the most detailed. I would characterize this tube as fast and clear. Easily the most transparent of the 4. Imaging was precise but the soundstage wasn't quite as wide and deep as the others. It was a bit lean though and personally as an all rounder, I prefer a bit more meat on the bones( fuller sound ). Tied with the National on treble extension.
Tun-sol; this is the tube that I expected to be my fav' after reading lots of posts on tube forums. It was the one that I used at the National as I didn't have time to burn in more than one. It is, in fact, probably the most balanced and all-rounder of the bunch. Wonderful soundstage, punchy bass, and a full smooth presentation. It isn't as resolving or transparent as the Sylvania or National though and seems a touch veiled.I think that this is a perfect example of the failings of A/B testing. If I'd never heard the other tubes, I never would have thought that it was veiled at all. I think it does have the best bass>lower mids of the group. I really like what it does with brass instrument, bringing them a bit forward and showing a lot of texture. I think if I listened primarily to jazz, this would be the tube I'd use,.. if it weren't for the National!
National-this was a huge surprise! The above tubes are easily the most highly touted 6sl7 types. The National was mentioned here and there as right up there with them but never raved about. The freq. response is balanced with no obvious peaks or dips. The transparency is very close if not the same as the Sylvania but the bass and mids are fuller. It doesn't quite have the bass extension of the Tung-sol but unless your looking for it, I'd never notice. It is smooth but not creamy like the RCA. What it does, that none of the others do, is magic! It puts a spotlight on musical line and follows the melody though whatever instrument the conductor chooses. This is apparent with concertos when there is interplay between say, the solo violin and the oboe, then the oboe and the french horn, to the french horn and the violin again. With jazz, the soloist pulls himself out of the crowd and there is more air around him till his solo ends. This tube is just heaven with female vocalists too. This tube in the context of my system, is musical to the extreme so I really had to force myself to evaluate what I was hearing. It was the last tube I tried and I thought that the Zana had gone through some milestone in burn in so I went back an forth with it and the Tung-sol and Sylvania.
RCA- this one's almost in a category all it's own. A little background first. Some folks have said that the ZD is not a tubey sounding amp. I agree. Neither is any of the tube gear in my speaker rig. It is the best, musical amp that I can afford though. I've had some very good ss gear ( Pass Labs X350) which sounded very good and does some things better than the tube gear I have now ( Conrad Johnson Premeir 140 ) but the tube gear has strengths which I won't do without. That said, the RCA breaks the mold and lends some of that classic tubey sound to the Zana. As said before, it has a smooth, creamy presentation. Highs never hurt, even if it's on the recording, and the bass is rounded and rolled off. This give it that phatt tube sound that musicians love in their instrument amps. It has great depth and a slightly narrow soundstage and is more veiled than the Tung-sol. But, it is a very pleasing sound and reminds me a little of a super, upgraded ASL mg head. A much more relaxed and laid back sound than any of the others that hails back to the classic Marantz tube gear. This tube does the most to change the overall character of the Zana and would be perfect for listening to when you really need to concentrate on something else at the same time.
I could easily live with any of the above but my preference for the National is obvious. I could offer opinions on which is better with rock or other electronic music, but I hate it when folks step outside of their realm of experience.
Once again, these impressions are with the ad2000 only! And with the 6 dt4 rectifiers ( although, I'll follow granodemostasa's lead and start to roll it as well).
