will
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So here is what I heard today.
I am using Valve Art KT66 rather than Genalex, so a little different, but in the neighborhood. These are more open and transparent than the Genalex by a bit, with less push and body. Not a lot, but some. With them I have been using Mazda GZ32s, British made 75C1 (OC2), 40's Sylvania OB3, and various PCC88s for inputs.
I put in some 6N23Ps marked like yours and they sound quite good. A little more forgiving than my usual PCC88s, but a bit less spaciousness, micro detail, extension, and dynamics. For tighter bass, I put in some Zaerix (Hitachi) GZ34 rectifiers, but with the 6N23s they sounded pretty dull. With PCC88s, they were pretty nice. They did open things up and tighten bass, but the 6N23Ps being dull by comparison indicates a difference between 6N23Ps and PCC88s. GZ34s have always been seductive to me when I first put them in, but then they start seeming too taught.
So leaving the 6N23Ps in, I put in my "go-to" RCA 5U4G-STs with top “hanging” D getters…Different. These allowed really nice open textures and micro detail from the 6N23Ps, in fact bringing out beautiful tone from the russian inputs. The RCAs are a clear improvement over the Ruby's in delicacy, micro detail, texture.... Very good toward the end of true transparency, they probably will not reduce your bass much, though it would be more refined.
Then I changed the slightly warm 75C1 to the stock russian OC2. They brightened it up some...and similar to the Ruby/RCA rectifier difference, the stock VRs are a bit tighter and less complex, but they are good. They feel more clear than the 75C1s with the balance a bit more to the mids, upper mids and highs, but it is more just a balance difference than resolution, the 75C1s being really complete. The Russians seem like pretty nice tubes though, especially for less bass/more bright.
Next I pulled the Sylvania 40s OB3s putting in the stock Russian OA3. The balance shifted toward bigger, more forward mids and bass… increased overall density. This also gave a less refined quality, less micro detail and associated delicacy of tone...they are harder and feel a little veiled due to less micro detail, though they are pretty bright. The greater push and harder edges concentrate the sound too much here. The end result is less detail balance, with a harder, pushier, less textured quality. This is a similar problem as the Ruby compared to the RCA 5U4G ST, the Rubys having less refined character. So far two of your tubes could be improved toward pulling better tonal refinements from the source….things ultimately critical to a real feel.
Then I put back the Mazda GZ32s...Generally, these particular tubes are a touch warmer and more defined than the RCA 5U4G ST, but they balance with their own style of sweet micro detail, and their special clarified ambience. There is a little more sense of density to the clarity and dynamics, but in this case it does not sound harder. The midrange is balanced with natural, smooth highs and the bass is less and a bit tighter.
I think I recall that the GZ32 is sort of between the 5U4G ST and GZ34, and it sounds that way. This is hard to put my finger on, but I really like these tubes and they sound quite good with the Russian VRs and 6N23Ps. The Mazdas are my nicest GZ32s for bass tightness, open ambience, and natural tone, next being a fat straight bottle GE with black plates and a round top getter, similar but more bassy by a bit. Then the RCA 5V4G (coke bottle shape) can be really good too, but in my rooms this is my least favorite being a little thinner mids up and a little less taught mid-bass down. The bass comes across different with all of them and may or may not solve your particular bass buildup problem area, but they do seem to have less bass than 5U4G STs.
With the stronger feeling bass of the GE 5V4Gs, and my usual OB3s, I tried RCA OB2s replacing the front Russian OC2 VRs. Tightened up the bass a notch. Nice, but a little lean for me.
Finally I put back my 75C1s (OC2) and some really nice 50s Siemens PCC88 inputs. This is awesome. Bigger bass, but tighter....open and textured mids…greater tonal density, extended and smooth highs...beautiful ambience. This tube set is GE fat bottle 5V4G, Sylvania OB3, Valve Art KT66, 75C1s and Siemens PCC88s.
Finally, the OB3 and OC3 are the first tubes I would explore. You will get more open spaciousness, micro-detail, and more refined warmth with NOS OB3s. Then a notch more openness and less push with OC3s. The best OC3s I have are coke bottle ST shape Hytrons from the early 40s. Hytrons are in their own league for openness, delicacy, textures, slight warmth and other aspects of musicality, things for which several of your tubes are lacking in various ways for ultimate sound. The other OC3 that is really nice is a Sylvania OC3W, with the big brown base that takes up most of the tube. Some call these egg beater shapes. They are warmer than the Hytrons, but nice. For increasing your transparency, the Hytrons would likely be better.
It would be nice to get some 40's Sylvania OB3s and OC3s. One or the other will be best and there is only one way to find out! I was told by an experienced tube dealer that he thought all the OB3s are Sylvania no matter the label, and the 40s tubes can be identified by a D shaped stabilizer welded to the middle wire just up from the glass base, but this is hard to see in pictures since these have a low getter flash. I found that by looking carefully at the 3 wires coming up through the interior glass blob, just above the tube base...if the 3 wires are evenly spaced in the blob, they are 50s tubes and a touch warmer and more textured. If the middle wire is offset from center, these are the slightly more open and dynamic 40s tubes. They are all good though...
So toward your objective of transparency and tighter bass, I guess I am thinking that ideally you would replace the rest of your tubes other than the power tubes, perhaps the OC2s being the best if you keep one pair, and the 6N23Ps next. You will not regret changing the rectifiers and OA3s. Both are limiting your potential for open complexity and refined musicality, and this will very likely help your bass also.
Then, changing the 6N23Ps to some decent PCC88s....I almost always like them best. All I have tried are nice, but like all the tube types, they have different signatures. They are generally extended, open and textured, with relatively controlled bass, likely good things for your setting. Several more reliably rise to the top though.
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