From Tommy: What are some real pretty rectifier tubes that sound great , work well in Decware amps, and are relatively inexpensive?EDIT: Sorry, I tripped up, calling a 5V4GA a 5Z4GA, close, but different...corrected below.I think a "good sounding" rectifier is pretty relative depending on system synergy and where you want your sound to go. There are so many variations in design, vintage and sound. So choosing one that goes in the sonic direction you want, in comparison to what you are using, could make or break how much you like it. For a 5U4G setup, like the CSP3, Zen, Rachel, and big Toriis, there are a lot of choices in 5U4Gs, and many more that are compatible.
If you are using a stock Ruby, or Valve Art, these are two different variations of that 5U4G-ST theme. If you like these, not a lot of change visually, but generally with more refined sound, are earlier RCA 5U4G-ST. I find the older ones tend to be more refined, but they can be nice into the 60s in their own ways. As far as those I have go, those with the big/thick black plates tend to sound bigger darker/warmer, and those with the slightly less massive plates tend to sound a little cleaner and less balanced toward bass. The lighter plates with top getters were my preference, to me more open, balanced and revealing of nuance.
From them, if you want to tighten/clean things up, and increase dynamics with spaciousness and fine detail, I agree with Joman, that the GZ32 type or Type 80 could be a good path. Most Euro made GZ32s are nice tubes, but tend to be costly. Other than the Russian GZ32/5AQ4 Joman posted, I prefer the balance of England/Holland made GZ32s, but you have to be diligent to find good ones relatively inexpensively, and those Russians are quite nice tubes...just not quite as refined to me. Worth a try if the type is appealing to your needs though.
5V4Gs are sort of American GZ32 "equivalents," different, but also dynamic, open and articulate, they tend to be in the neighborhood. Especially old fat bottle 5V4G
As can be pretty nice, while looking interesting too, and relatively inexpensive. Especially the ones with rectangle getters might be worth searching Ebay a bit. They tend to be quite clean, open and detailed, the older square getter ones I have going deeper and warmer while remaining dynamic and clear...Depending on what they are with, some of the type can be a little too clean. But often for even better value than the Russian GZ32s, they could be worth a try if you are looking to open things up with more dynamic articulation.
I like type 80s too. I have been using one in my CSP3 for a really long time. For cool looking, globes are well worth checking out. They are sometimes pretty costly and others not-so, especially if you only need one. The one I am using is a Philco with engraved base, cleaner/more open sounding than the Cunnninghams I have, but the Cunninghams are a good choice if a little more warmth is needed. This is the tube type Steve currently pictures in the 25th Zen. I think they tend to be a little less fine detail and dynamics oriented than GZ32s, but have a very nice spaciousness with these qualities present in a relatively convincing, balanced way.
I also like type 80 STs (coke bottle shape) Joman mentioned, tending to be tighter and more focussed sounding than the mellower, more complex Philco globes, but definitely family and possibly preferable depending on needs. Looking a lot like Euro GZ32's, made tall by the necessary adaptor, depending on taste they can be pretty nice to look at too. I have one Pope labelled, made in Holland that is my favorite, a little more focussed than the globe, but still showing ambient space and texture very nicely. Similar, a step further into focus but still pretty complex, and a little less dynamic, is an old Tungsol Type 80 ST. The Westinghouse I have sounds pretty good, but is just a bit murky down low and rigid for me, lacking a little of the complexity the others offer. But these are tell-tale signs of a new tube. It may be true NOS, not burned in, so hard to say.
For GZs and 5V4GAs adaptors are not needed. Type 80s need them, but they are pretty easy to get.
You can search on Ebay with 5Z3 to 5U4G adaptor and see if any suit you, something like this:
https://www.ebay.com/itm/1-PCS-gold-plated-Adapter-for-5Z3-5U4G-80-5Y3-tube-SUB-...A word of caution on the square hole 5Z4 to 5U4G adapters. It is possible to feel like you are fitting the pins correctly and have them in the wrong position, and then fry the tube. Best to look carefully at the pin spacing and sizes in relation to the socket spacing and sizes.
People who want the spacious dynamics of GZ32s, but with more power/push often go for Mullard or Phillips Holland GZ34...a similar, but bigger/warmer, more forceful sound than its electronically more chill little brother, the GZ32. They tend to be quite costly too, but with patience occasional buys show up. Preferring GZ32, GZ34 are too big and warm for me, but folks who love GZ34 likely find GZ32 a little lean. They are pretty plain looking little rectifiers, so may not fit your request, but a very popular "standard" for sound.
With similar tight bass and dynamics as GZs, and generally with quite a big spaciousness and good fine detail, is the 5R4GY type. Warmer ones I have tried are Phillips 5R4GYSs, a tube I personally could never get, finding it a little veiled. A wild looking, and very reasonable, Chatham "potato masher," also a little warmish, and not quite as open and detailed as some 5R4s, it sounds natural to me, open without a lot of risk of going too far. Stepping out from stock 5U4Gs or 274Bs it could be a nice shift into increased articulation with dynamic spaciousness, but not as far out on that limb as some others. RCA 5R4GYs are widely variable in price, sometimes pretty inexpensive. Some love them and others find them too clean. I find it depends on everything else. If the balance is really clean, the RCA can take it too far. But if you want to open things up, they can work well. I like the old pair I have, in my setup, slightly warm, dynamic and clear, but for me it rarely stays in. The most balanced 5R4GY I have, while being super spacious, is a Fivre I got from an English seller, a nice, big and open rectifier. Of these, I would say the Chaham, if the look appeals, is a good one to dip a toe in with for the type.
In the Torii IV I just replaced some rare 40s Telefunken RGN1062 globes (need adaptors) I have been using a few years, with some Sylvania fat bottle 5V4GAs (square getters). And a Type 80-ST Pope in the CSP3 in the place of the Philco Type 80 Globe. Combined, it is fast, open and harmonically rich...deep, warm and dynamic...in this setting anyway. First impressions, I had to adjust gains a little, but once tuned, I find it a little warmer, focussed, and more dynamic than what I had...to me really good warmth, the darkening touch not overwhelming spaciousness and fine detail, but richening it, and the focus not overly combining fine detail and textures. Sounds great so far in my setup.