In my Toriis, once I tried them, instead of 5U4G-STs mostly, I generally preferred Philips made ST coke bottle shaped GZ32 and used variations for years. My fav
here was a Mazda with double bottom rectangle getters, the cleanest of the ST shapes I tried but also fast, smooth and resolving. The same shaped Mullards I have are warmer, and Philips Holland closer to the Mullards, but in between. In my already warmish setup, I liked the Mazdas better, less noticeable as to the tube having a sound
here anyway. But in another leaner setup, the Mullards would likely be better.
I got tighter/faster bass with 5V4 or GZ32 over 5U4s also, making it sound like it brought bass up, but I am pretty sure they actually bring the bass down enough to speed it up and let it "breath" more space. My theory is that the 5U4s tended toward a little too much bass in my setting, making them tend thicker/fuller and shifting the balance to darker/slower overall. And I think the GZ32s or 5V4s are faster and tighter by nature, with more sense of space, but being a little less powered up, less bass also. So if the system is a little thick/dark, the resolution seems better with the milder faster tubes, in part because they do not push the other tubes as hard. This "push" is throughout the way I hear it, but if the bass is close to muddle in a system/room, and the rectifier goes a little too far, the extra bass push seems most noticeable because it gets so full it falls into being less resolved... too thick.
I feel pretty confident I have corroborated this theory in this system/room with experimenting with other tubes, the bassier, more powerful choices often exciting room modes more, or just plain being a little full dark in my amp, and for my tastes. If I use a little cleaner/less powerful tube (like nice PCC88s or nice ECC88 variants in the place of E88CC) the milder push conveys across the spectrum... less powerful/forceful, less concentrated, but again, even with inputs, the bass, if it is off, can tend to show easier if it is closer to those subtle edges of good speed and resolution, and getting a little overwhelming...
Liking bass that is naturally full, but also tightish and textured (no masking really).... when something is little too much, fullness can start to slide into variations of muddle and/or boom, while the darker tone balance leaks darkness and fullness into the mids.
Cables also... I have found variations, but generally, if a power cable of a given design and materials is too big, it seems to bring with it a sort of compression that slows, darkens, and thickens the whole. And if I back it off a little gauge wise, it opens a little and I find the beauty balance. Same with ICs and speaker cables for me.
Personally the RCA 5V4s (coke bottle ST shape) I tried, I think '52, were a little dark/slow/warm for me. But I found GE and Sylvania fat bottles on the too clean side. Again, my system, but the latter worked a little better. The rectifier being so influential on all else, the RCA was not ideal for my setup and needs. Whereas the Sylvania fat bottles being quite clean but smoother and a little less super clean than the GE fat bottles, I could warm them up with other tubes and have the clarity and speed I wanted, with other tubes warming the whole up enough that the fat bottles were not too much. In another leaner system, I suppose I could prefer the RCAs ???
Whereas, the clean Mazda GZ32s were fast and resolving, and not overly dark or overly clear
here, so I used them for a long time...
Later I got into some specific 4 volt Euro tubes like AZ11s, or RGN-1064s, these types having the same electrical values but different pinouts and adaptors... but out on a limb, having high cap ratings, but being 4 volt and the amp set up for 5. I used them without many issues for more years than the GZ32s... a lower sense of power, but very musically resolving tubes, so not in the face, and not missing anything
here especially since I almost always prefer a little less bass balanced rectifiers here. That said, to me they have a pretty close resemblance overall to the Mazda GZ32, but better resolution to me... more fine detail in open space. The nice ones are really well made older tubes... a lot from the 30s and Telefunken or variants, straight bottle and globes, or Philips Holland globes... some of them with solid plates, and some mesh. I have no idea about recommending these though... I have never heard from anyone who really knows if there are any issues except the possibility of the mesh plates frying with more voltage than rated... but I don't think that happened in my amp but one or two times, and am not sure with these old tubes, perhaps some more vulnerable for other reasons and the voltage pushing them a little too hard as well??? And I did pick up a bunch of them over time as good deals came up, so was rolling them. But I think some of them stayed in for a few years... So I can only say I really like the sound here, and it may be in part because the Torii IV and HR-1s seemed innately a little bass heavy in the balance, for me anyway, and before I opened them up some. But even then I still tend to prefer this tube type, and have for a really long time.
A caution if you go for GZ32s, I am not positive, but think it was some of the earlier ST shaped Philips-made tubes that had a different cathodes setup, with narrow tubes and vulnerable cathodes. I got some Telefunkens and Darios with narrow cathodes tubes before I knew better, and both sounded great for a bit, but fried pretty quickly. I have not seen Mullards this way, but don't know if there were any, and most GZ32 I have seen in the past did not have the really narrow cathode design. But the thing to do is avoid those ones with the really small diameter cathode tubes. I am putting up a picture. It is a little hard to see the tops of the cathode tubes coming through the top mica, especially the little ones on the right hand Dario, versus the bigger ones on the left hand Mullard. I would avoid the ones like the right one.
Not sure as I have not tried a lot, but the few fat bottle Philips GZ32s I have are on the cleaner sounding side of STs, even cleaner than the Mazda STs some. And the Brimar STs, to me were obviously really nice tubes, but more intense... more consolidated, which did not appeal as much back when I tried them. It might now, and it might in your amp though. Anyway, hope this helps.
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