You are quite the mixer and matcher of good tubes Lon. I can imagine how the pinched waste 7062, being quite powerful/fast/clear but smooth for a 12AU7 variant....feeding the grey glass RCA 6SN7s, notably warm and a little slowish by contrast, yet having quite good space and resolution within that....and then the powerful, extended, warm, yet also resolving 300-Zs. It makes sense that these could well compliment one another with a magic beyond any one of them. Maybe a little too dark and full for me, but maybe not with the additional 7062 in the ZRock and careful gain balancing... and I can totally get it how this combination is singing in your room!

Yes, finally so dependent on conditions... but thankfully we can recognize basic sound characteristics of tubes, cables, components...  and imagine how those traits will work in our system/rooms.

I always like reading your tube set posts. They often remind me of tubes I have not in the past ever fully gotten, but having recognized compelling traits, now and then I like to check in with them as the system changes... Or maybe you remind me of tubes I may not have used in a while... Or your explorations trying combinations of nice tubes with different inherent signatures, especially extra warm and a little slower along with extra clear and faster, sometimes the balance between being really good.

I guess the latter is most the case for me just now. I have always really liked the Amperex 7062 pinch waste, but my components and room have been so progressively tuned for easy revelation, speed, space and resolved clarity, that this tube usually ends up too strong in all the good things it does...overstated.

But now, burning in some powerful and bass/warm balanced Linlai 845-DGs, driven by Linlai WE300B replicas which are a little warmish but mainly spacious and resolving, and some clear but smooth Raytheon short bottle 6SN7 GTBs in front of the 300Bs... The 845-DGs still could overwhelm on darker recordings, their darkish and thickish bass leaking up into the low mids... They sounded truly amazing on less bass oriented recordings though, so I really want to get through the burnin with more consistent beauty across recordings, knowing the bass on big powerful tubes often takes a long time to resolve.

So I opened up the CSP3, replacing some very neutral and resolving Valvo E88CC/6922s as power tubes, with some milder but also clear, fast, and resolving Amperex ECC189s. By reducing the power of the output tubes some, it opened up the CSP3 nicely.

In the ZR2 I replaced a complex and textured Amperex orange label 12AU7 with a nice older tube with a horseshoe getter, a go-to 12AU7 for extra open clarity that is smooth. I can't remember the make of it. The sound was really good then, balancing the 845s, but I figured more power behind the clarity before the 845s might just work in this case. So I put a Holland 7062 pinched waste in the ZR2, and the sound is gorgeous, even with quite warm/bassy recordings.

Maybe for the first time, the powerful spacious clarity of the pinched waste 7062 that tended to overpower my usual tube sets, is very useful and beautiful... strong enough to cut through the darkish density of the 845s as they burn in, while allowing all the tubes to do their things better.... Fast, rich, complex lucidity with beautiful and musically touching balances!

I went through some tube-rolling again today and came back where I started. And then I remembered I had some 6CG7 which are 9-pin equivalents of 6NS7, and I found a pair of RCA clear tops that sound quite nice--clearer, a bit more dynamic than the RCA gray glass 6NS7, though with less warmth and pace, at least so far. A nice change with some material, I'll let them season in a bit. I should have more, I'll keep looking and I found a pair of GE on ebay that I have on the way.

It's amazing how flexible and "pioneering" these amps can be. Thanks to the tubes Will sent I'm really into another dimension of sound now, both accurate and slightly euphonic--just my type of sound.

It is amazing what similar sound shaping tools can do to bring out subtly different qualities from all the other sound shapers that make up a system and room.... and how synergistic the end feeling can be from seemingly pretty small changes!

I have so far not been able to keep in gray glass RCA 6SN7s in any of my amps, always respecting them, but finding their style of warmth a little too obvious... the ways they balance toward bass here slightly masking some areas of fine detail...And the slight slowness with that (here), lacking some space and associated immediacy of leading and trailing edges I need. With system and room clearly a big part of it aside from preferences, and since you are exploring tubes a lot lately, I hope my experiences in a different system and room, using similar quality sound tools, might help some folks less tube crazy than us.

I am really glad those Preferred Shuguang 300Zs are holding up for you. They were characterful tubes here with nice density, coloration and resolution qualities... and it is fun knowing that if a little warm leaning for me, or too strong for my setup, these same traits could cause them to work well in yours!

Following your lead, I have been playing with various 12AU7 types, in positions they were designed to be used, and in E88CC positions with adapters. A few things in the pot, some minor bypass refinements in the CSP3, still smooth and a little sweet, but a little more neutral and fast, so more flexible with gain adjustments; new wires in my Omegas (more neutral, faster and more resolving); and still tuning in the Swiss Digital Fuse boxes with hollow fuse replacements, getting to where they do good things without overstating the sound and coloring my system slower and darker like using all solid copper and silver tends to do. Now I have 4 hollow silvers, two with Rhodium, and one solid silver.

But the 12AU7s...   the flavor of 12AU7 types with adapters in E88CC positions I always find seductive, but in the past, finally they tend to sound a little unreal to me. Initially, I always like the sense of clarity and space they musically bring. But finally there is, for me, a difficult to grasp sort of leanness. Maybe it is that the added spacious clarity comes with a little less super fine detail??? leaving them a little empty here... I have to listen more and see if I can figure it out... But lately, this is not the case, the warmish pair of red top 12AU7s you sent me in the power positions of the CSP3 taking my music to amazing levels.

As I mentioned earlier, the pinched waste 7062 in my ZRock sounded pretty right, its resolving power cutting through some darkness I was having from new power tubes... But once again, that didn't last. The added power in my extra resolving ZRock, compared to nice old 12AU7s, put me a little closer to the signal being too powerful, and a little closer to distortions in the context of several pre stages in a row. But more, it just sounded "too good." The 7062 powered up the whole nicely in the many balances, but ended up sounding a little too right... a little hifi.

Then I tried them with adapters in the power tube positions of the CSP3 as a pair... this was even more impressive, two together, and showed more of the warmth of the tube. Very resolving as well, they sounded great, but more dominant in the whole. Then I heard it... though beautifully done, they were filling in too much of the space.

I lost a little of the anticipation of sounds coming out of empty seeming space I had grown dependent on... that weird thing of incredibly resolved fine detail in space that comes  from such good timing that you hear more without it feeling harsh if right...those magical places where subtle smearing interferes less and less, making it music rather than a representation of it.

But being the first time I had used 12AU7 types in a 6922/E88CC position where it sounded pretty right, I took the hint... trying the less powerful red top 12AU7s... and after 4-5 days I guess, they still sound great in all balances... with less power, they allow a really natural sounding fine detail clarity in space that is not obvious but quite a contributor to a seductive musical experience. Along with the hollow fuse replacements they open up the big bass balanced 845s with amazing natural warmth and a beautifully complete space and detail complexity... I have more flexible balances that allow pushing my pre stages into lucid territory without getting too dense and full.

But it is even better... though I can pick it out, it does not sound like amazing complex detail and space. Instead, I am better able to hear all the natural complexity of the music and without trying... It was sort of amazingly revealing, and now it is all more completely revealed. It feels like the players conveying their emotions and expressions with less limitations...the space to sound relationships so naturally fast that you don't hear it as fast... more free flow.

At this level, on a decent solo violin recording, its like I can feel the tension rising for the next pull of the bow before there is sound... and once there is sound, the many subtle qualities that make that sound, string, bow hair, rosin, bridge and tail piece, woods... all the parts and qualities of the instrument unite, but are also differentiated enough to hear them specifically but naturally.

This completeness opens the experience into a landscape of gorgeous interactions, the most revelatory, being so much a part of the musical expression that the energy between the notes, leading to notes, is part of the experience... then with fundamentals and amazing harmonics, the player, the bowing, and each part of the violin are alive with the music and all that makes it...

I think this is in large part due to more complete space. Last night listening from my bath tub down the hall, where it is like the whole system room is the speaker, I spontaneously noticed the subtle string/bow connections shift and flow... even hearing the tension between the tail piece and bridge, and how the face wood vibrates harder, but with slightly damped harmonics when there is more pressure on the bow... pushing the bridge harder, and thus the face and sound post... those subtle things you hear if you are playing the violin in a good room... It did not feel like the details of differentiated sounds in differentiated space, though it was the revelations of such a complex of balances that seemed to make the magic work.

So more and more I think I am finding, that with good time, you not only hear more complete musical information (if it is there in the source and beyond), less smearing equaling more articulate and complex detail. But perhaps more importantly, less smearing creates more articulate space, which reveals even the subtlest sounds with more presence and complexity. When space and detail are balanced, I am always sort of shocked how it also feels more relaxed... more complete space, detail and speed relationships making the pace of, especially slower music, sound slower... more relaxed...

Long lead up to how tuning balances with tubes and all else, can turn really good sound into something beyond sound... mysterious and intoxicating...

These Sylvania 6GC7 seem to be the cat's meow for now. They have given just the right frequency and dynamic control to the system. The pinched waist 6085 and C751 and Black Treasure 300B-Z and Aqua 274B II seem to just love to work in harmony with them. In contrast to when I was running Cryotone tubes in this system this complement is more musical and natural sounding.

In contrast I have been using nearly all Cryotone (all but the rectifiers) in my audio/visual system and the sound is great there. The room is twice as big and I can sit farther from the HR-1s there. I think that's the secret: a bigger room changes everything.

Yes I am that pleased with the sound I am getting right now.

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Seems like you've kind of made a full circle, back to the 5V4G tubes you were using years ago. I always thought the 5V4G was just the US name for a GZ32 and that it might be a little underpowered for a 300B amp. But the RCA datasheet says 175 mA (same as the GZ43/5AR4) so I learned something. Regardless, it is really nice to have a stash of old tubes lying around.

With three hours on the Snubway I swapped in the Zenith 5U4G and it is like Goldilock's porridge today. . . just right.

After looking at quartz slabs a few hours this afternoon being in front of the stereo is a delight.

I will say this: this amp really reacts to rectifiers. I'm leaving the Aqua II in and hoping that it remains trouble-free as with it my favored complement of NOS tubes just SHINES.

I've got everything dialed down and the only tubes I am going to experiment with a bit are the 6CG7 that I am using as drivers for the 300B-Z. I have a pair of black plate Westing House coming in today that will be my next trial pair.

One other note: more and more I realize how influential the gain structure between the components is. I've mainly been leaving my DAC "preamp" and ZROCK2 volume static and playing between the gain of the ZBIT and the SEWE300B. Drastic changes to these gain settings can be like switching in a different amp! It can be thin and detailed and tremendously dynamic. . . or rich and present and revealing and many "amps" in between. These are amazing products.

Yes, the amp gain seems to be the most influential element in my system much of the time.

I have not been able to get too many hours on the Cryotone 5U4G in the audio/visual system--will take a few months to get a few hundred hours on it. The Zenith 5U4G is an excellent tube--I would not say it is softer than the Aqua II but it is less . . . black backgrounded and a bit less dynamic. Rolling a few other tubes can make it really wonderful. . .an alternative for when I get bored or encounter recordings that need a different "window."

Well, the fact that this is an amp with a preamp within I think makes a significant difference from the other amps that are not "integrated."

It is mainly the gain parameters that are set by those upstream from the amp that enable the amp to be the "final gain arbiter" so to speak and in that sense the most "important" gain element for the final shape of the sound.